Electronic device, method of operating and method of calibration thereof

Abstract

The present patent application relates to the technical field of energy harvester and, in particular, to an electronic device 0 comprising a power monitoring system, to method for estimating the amount of energy transferred by a DC-DC converter and to calibration methods for a power monitoring system of the invention.

Description

Electronic device, method of operating and method of calibration thereof.

[0001] Description

[0002] The present patent application relates to the technical field of small electronic devices powered by a battery and an energy harvester and, in particular, to a power monitoring system for monitoring energy transfer in a DC-DC converter. According to others of its aspects, the invention relates to an electronic device comprising such a power monitoring system, to methods for estimating the amount of energy transferred by a DC-DC converter and to calibration methods for the power monitoring system of the invention.

[0003] Prior art

[0004] With the widespread deployment of connected devices, particularly within the Internet of Things (loT), the challenge of powering these devices has become more prominent. Traditionally, many loT devices rely on batteries as their primary power source. However, the frequent replacement of batteries presents several issues, such as environmental impact due to battery waste, added costs associated with labor for battery replacements, and inconveniences for users. These concerns have driven developers to explore alternatives to traditional batteries.

[0005] One such alternative that has gained popularity is energy harvesting. This technique involves capturing energy from the environment. Energy harvesters capture small amounts of energy from various natural and artificial sources to power low-power devices, enabling self- sustaining systems. Mechanical energy from vibrations, kinetic motion, or pressure changes can be harvested in industrial settings or from human movement, while fluid flow and airflow also provide opportunities for energy capture. Thermal energy, derived from temperature gradients or waste heat in industrial equipment or even body warmth, can be converted into electricity through thermoelectric generators. Light energy, both from sunlight and indoor artificial sources, is widely used through photovoltaic cells for outdoor and indoor applications alike. Radio frequency (RF) energy, present in ambient signals from Wi-Fi, cell towers, and other communications sources, can power ultra-low-power electronics, with dedicated RF sources providing wireless charging for some devices. Additionally, biochemical and electrochemical reactions, such as those occurring in biofuel cells or corrosion processes, offer energy for specific applications, including medical and underwater sensors. Electrostatic methods also convert electric field fluctuations into usable energy, and triboelectric generators exploit contact and separation of materials to capture power from repetitive movements. This diverse range of sources enables energy harvesting in a variety of environments, providing reliable power for remote sensors, wearables, and other compact, low-energy devices. Energy harvesting reduces or eliminates the need for battery replacements, providing a more sustainable solution. However, despite its potential, energy harvesting presents significant technical challenges, particularly in maintaining consistent power levels.

[0006] A fundamental issue with energy harvesting in such low-power applications is the variability in the energy available from environmental sources. The amount of energy that can be harvested depends heavily on external factors such as light intensity, vibration magnitude, or proximity to an RF emitter. These environmental conditions can fluctuate dramatically, leading to unpredictable energy availability. This makes it difficult for energy-harvesting systems to operate autonomously without external power support.

[0007] For a truly autonomous system, it is crucial to have real-time insight into the amount of energy being harvested and transferred to the storage device, such as a battery or capacitor and the amount of energy being transferred from the storage device. Without accurate monitoring of the power flows, the system risks either underutilizing the available energy or overloading the energy storage. Moreover, the problem extends beyond energy-harvesting systems: in battery-powered devices, knowing how much power is being transferred to or from a DC-DC converter can provide valuable insights, such as estimating the remaining battery life.

[0008] It would therefore be advantageous to provide a power monitoring system for monitoring in real-time energy transfer in a DC-DC converter. Such power monitoring system should be able to provide real-time information about the power transferred from a power input (for example an energy harvester or a battery) to an output (for example a storage or a component using the power).

[0009] Advantageously, such a power monitoring system could also be usable with disposable batteries that are not meant to be reloaded after use.

[0010] US-A1-2014 / 327467 discloses a system for monitoring and controlling energy consumption in electronic devices, particularly those powered by a DC-DC converter. The system uses a pulse signal generated by the converter to measure, without interfering with its operation, the amount of energy transferred to an electronic circuit. The monitoring relies on pulse-width measurement logic, input and output voltage sensing, error detection, and a calibration circuit. The system can detect errors such as overvoltage, undervoltage, and overcurrent conditions, and compares the measured parameters with predefined thresholds. A calibration load is used to obtain a reliable reference for correlating pulse duration with transferred energy. The resulting data are communicated to an energy-monitoring unit, which can determine the energy consumed by the circuit. The system can also predict the remaining lifetime of the energy source and profile the circuit's energy behavior. In cases of excessive consumption, it can adapt the circuit's operation dynamically, for example by reducing its operating frequency or switching to an alternative mode.

[0011] US-A1-2016 / 048197 relates to an electronic circuit and method for measuring the power consumption of integrated circuits, particularly in low-power modes. Instead of relying on complex external circuitry, D2 instruments the switching power supplies themselves (buck converters or switched-capacitor regulators) to count their switching pulses. Since the energyper pulse is known, the total consumption over a given period can be estimated. Two operating modes are considered, PFM and PWM, each with its own counting approach. Internal counters, synchronized to a clock, enable pulse and reference counting, and the resulting data can be accessed by the central processor via a system bus. A calibration mode using a known load allows conversion of relative data into absolute current values, while dedicated power-trace pins facilitate external probing. This approach enables embedded applications to become aware of their own energy usage, allowing dynamic power management to extend battery life.

[0012] Those documents do not disclose a monitoring of the inductor charge and discharge cycles rather, they only monitor the switching control pulses.

[0013] Summary of the invention

[0014] According to the invention, this problem is solved by providing an electronic device comprising one or more inductive DC-DC converter(s) configured to transfer energy from one or more input(s) to one or more output(s). According to the invention, at least one of the DC- DC converter(s) is an inductive converter using an inductor as reactive component and operates in discontinuous mode and is configured to stop the charging of the inductor when a current IMAX has been accumulated in the inductor, a power monitoring system for estimating the amount of energy ( EEST) being provided at one or more input(s) or being delivered to one or more output(s) of the DC-DC converter(s). The power monitoring system of the invention comprises an activity monitoring circuit configured to count at least the amount of charge and discharge cycles of the inductor. These cycles are representative of the operation of the DC-DC converter and provide one or more count result(s). The activity monitoring circuit counts the amount of charge and discharge cycles of the inductor, but several other events can be counted simultaneously. The power monitoring system of the invention also comprises a logic controller configured to estimate periodically the amount of energy EEST based on i) the activity monitoring circuit count result(s) and on ii) one or more parameter(s) Ei, Ej,... Exthat are a representation of the amount of energy being provided at one or more input(s), or being delivered to one or more output(s) of the DC-DC converter per event counted by the activity monitoring circuit. The power monitoring system of the invention also comprises a timer configured to set the duration of the time frame TMON during which the amount of energy EEST is estimated by the logic controller, in order to provide periodic results over consecutive time frames and a memory unit configured to store the results of the periodic estimations.

[0015] According to the invention, the monitored inductive DC-DC converter operates thus in discontinuous mode and the events counted by the activity monitoring circuit are the amount of charge and discharge cycles of the inductor. Indeed, as the DC-DC converter operates in discontinuous mode, the energy in the inductor is equal to 0 at the beginning of the charge cycle and goes back to zero at the end of the discharge cycle. During each cycle, the energy stored in the inductor thus first, during an accumulation phase, increases to a maximum valuethat is a function of the current being stored in the inductor at the end of this accumulation phase. The energy transferred by the DC-DC converter is thus a function of the number of charge-discharge cycles, and of the current being accumulated in the inductance during each cycle. It is thus possible to evaluate the amount of energy transferred during a single cycle according to different parameters of the DC-DC converter, including at least the maximum current in the inductor during a charge-discharge cycle.

[0016] In a preferred embodiment of the invention, the memory unit is configured to store one or more result(s) and to output a signal at an output of the power monitoring system when a preconfigured number N of results are available. Number N can be any integer from 1. Typically, N is an even number. Typical values are comprised between 8 and 128. Thereby, the communication interface to read the results stored in the memory unit is triggered less often, reducing the energy cost of the acquisition of those data. Results can be transferred to and stored in the memory unit individually (one by one) or in a batch. Alternatively, their sum or their average can be transferred to and stored in the memory unit for further reading. The output signal can be a simple flag set to a predetermined value.

[0017] In an advantageous variant of this embodiment, the logic controller is configured to perform a logic operation on the results stored into the memory unit when the preconfigured number N of results are available and to store the results of this logic operation in the memory unit. The logic operation is an evaluation of the average value of the stored results or the addition of the values of the stored results. By reading only the result of this logic operation, the data acquisition energy cost is further reduced.

[0018] In another embodiment of the invention, the power monitoring system of the invention further comprises a first voltmeter configured to provide numerical representations of the input voltage(s) of the DC-DC converter to the logic controller or a second voltmeter to provide numerical representations of the output voltage(s) of the DC-DC converter to the logic controller or two voltmeters configured to provide numerical representations of the input and output voltages of the DC-DC converter to the logic controller.

[0019] This numerical representation of the input and / or output voltage(s) of the DC-DC converter allows providing meaningful information to the power monitoring system in order to refine the accuracy of the energy estimate EEST by tracking the real input and / or output voltage(s) of the DC-DC converter rather than preconfigured values.

[0020] In another embodiment of the invention, the power monitoring system of the invention further comprises a current sensing circuit (for example an ammeter) configured to provide numerical representations of the input current(s) of the DC-DC converter to the logic controller or a current sensing circuit (for example an ammeter) configured to provide numerical representations of the output current(s) of the DC-DC converter to the logic controller or two current sensing circuits (for example ammeters) configured to providenumerical representations of the input and output current(s) of the DC-DC converter to the logic controller.

[0021] This numerical representation of the input and / or output current(s) of the DC-DC converter allows providing meaningful information to the power monitoring system in order to refine the accuracy of the energy estimate EEST- The numerical representation of the input and / or output current(s) of the DC-DC converter allows performing the evaluation of EEST if the peak current in the inductor is not preconfigured.

[0022] Advantageously, the parameters Ei, E2, ... Exare stored in a lookup table which is part of the logic controller.

[0023] With the use of a lookup table, the logic-controller can estimate the energy transferred per event counted by the activity monitoring circuit without requiring complex logic circuits such as multipliers, adders, etc. that consume a significant amount of silicon area.

[0024] Alternatively, parameters Ei, E2, ... Exare computed by the logic controller with a logic function implemented by combinatory circuits or a program.

[0025] With the use of combinatory circuits or a program, the logic controller can estimate the energy transferred per event counted by the activity monitoring circuit with a better accuracy than with the use of a lookup table. Indeed, with a lookup table, the resolution of the parameters Ei, E2, ... Exthat provides the energy transferred per event counted by the activity monitoring circuit, is limited to the resolution of the lookup table itself. This resolution of the lookup table is a direct function of the silicon area dedicated to the implementation of the lookup table. When a certain level of resolution is desired, it becomes thus more efficient, from a silicon area point of view, to use hardware accelerators such as combinatory circuits. The use of a program, when computing resources are available, fully avoids the use of dedicated hardware, and thus of silicon area dedicated to the evaluation of parameters Ei, E2, ... Ex. However, as this evaluation is then not performed by a dedicated hardware, it generally consumes more energy and can take longer.

[0026] The duration TMON set by the timer is either fixed or dynamically controlled by the logic controller.

[0027] A fixed duration is easier to implement. A dynamic duration allows adapting the time interval between the availability of two consecutive evaluations of the energy EEST according to the activity or to the status of the application supplied by the output of the DCDC converter or by the storage device being supplied by the DCDC converter. A dynamic duration also allows adapting the duration of the energy evaluation to change of parameters influencing the energy being transferred per event counted such as a change of the input voltage, which eases calculation of the evaluation result.

[0028] In a particularly interesting embodiment of the electronic device according to the invention, the logic controller is configured to perform a calibration process, preferably an auto-calibration process.

[0029] To this end, the power monitoring system can comprise a circuit configured to provide a known current lREFto one or more input(s) of the DC-DC converter and the logic controller includes a second memory unit configured to store the expected results of the power monitoring system conversion depending on the one or more input voltage(s) of the DC-DC converter and on the known current lREFand optionally on the one or more output voltage(s) of the DC-DC converter. The logic controller is further configured to provide a target regulation voltage to the one or more input(s) of the DC-DC converter wherein the known current lREFis provided; and to provide a control signal to disconnect the one or more input path(s) between the energy source and the one or more input(s) of the DC-DC converter. The circuit configured to provide a known current can be a simple current reference or can include resistors connected between a known higher voltage and the target input voltage.

[0030] The calibration is useful as some parameters that play a role in the evaluation of the parameters Ei, E2, ..., Excannot be constant from one implementation to another. These fluctuations, while unknown by the power monitoring circuit, affect the amount of energy being transferred per event counted by the activity monitoring circuit. For instance, the actual value of the inductor used as the reactive component can vary by several percents from one specimen to another. Other parameters impacting the control of the DC-DC converter such as internal bias can also impact the behavior of the DC-DC converters. A calibration process allows adapting the result of the power monitoring system according to those fluctuations. Further, an auto-calibration process does not require any external action by the user, easing the production process. It also eases the taking into account of parameters fluctuating over time, such as external temperature, as the auto-calibration can be made periodically.

[0031] In an alternative embodiment having similar advantages, the power monitoring system comprises a current sink sinking a known current IREFB to one or more output(s) of the DC-DC converter. It must be noted that IREFB can be fixed or proportional to the output voltage when a resistive circuit of a known resistance is applied. The logic controller includes a second memory unit configured to store the expected results of the power monitoring system conversion depending on the one or more output voltage(s) of the DC-DC converter and on the known current IREFB and optionally on the one or more input voltage(s) of the DC-DC converter. The logic controller is further configured to provide a target regulation voltage to the one or more output(s) of the DC-DC converter where the known current IREFB is sunk and to provide a control signal to disconnect the one or more output path(s) between electronic load(s) and the one or more output(s) of the DC-DC converter or to put the load(s) in a state where their consumption is minimum, meaning neglectable when compared to IREFB, or known.

[0032] An electronic load has to be construed as any integrated circuit such as but not limited to a sensor, a microcontroller, wireless communication means, or as a circuit implementing another function and included into the same integrated circuit as the DC-DC converter or as the power monitoring system, or as discrete components such as but not limited to resistors, LEDs or transistors.

[0033] In an embodiment, the electronic device of the invention comprises a plurality of DC- DC converters, each being configured to transfer energy from one or more input(s) to one or more output(s), a storage device (for example a battery or a capacitor) connected to one of the one or more output(s) of a first DC-DC converter(s) and to one of the one or more input(s) of a second DC-DC converter(s) and electronic loads (for example a sensor, microcontroller or wireless communication means) connected to the one or more output(s) of the DC-DC converters. In that embodiment, the power monitoring system monitors the net energy transfer in the storage device.

[0034] In many use cases such as fuel gauging, which stands for the process of estimating the remaining energy in the storage device, a relevant information is the energy flow in or from the storage device. Providing an estimation of the net energy transfer avoids the burden of doing this calculation based on the energy estimates from each device connected to the storage device, minimizing thus the amount of data to be acquired and the associated energy consumption.

[0035] Operating the inductive DC-DC converter in discontinuous mode is more energy efficient when the amount of power to be transferred by the inductive DC-DC converter is small, typically below 1W or a few hundreds of mW.

[0036] As already indicated above, the monitored inductive DC-DC converter is configured to stop the charging of the inductor when a current IMAX has been accumulated in the inductor. Preferably, I AX is either predetermined or dynamically adjusted by the logic controller.

[0037] The energy transferred by the DC-DC converter is a function of the current IMAX- Therefore, preconfiguring it to a known value ease the calculation of the energy transferred because this energy can be considered as identical for each cycle as long as other parameters such as input and output voltages of the DC-DC converter remains unchanged.

[0038] IMAX can be known to be reached thanks to a current sensor measuring the current flowing in the inductor or in a power transistor of the DC-DC converter that is conducting in the charge accumulation phase. An alternative to this current sensing would be to stop the charge accumulation phase after a predetermined time, corresponding to the time required for an inductor of a known value to accumulate a current IMAX- This time can be calculated based on the knowledge of the voltages across the inductor during the charge accumulation phase.

[0039] In a variant, the one or more parameter(s) Ei, Ej,... Exare a function of at least three parameters selected amongst the following parameters:- the one or more input voltage(s) of the DC-DC converter,- the one or more output voltage(s) of the DC-DC converter,- the peak current IMAX reached in the inductor,- the size of the inductor used as the reactive component of the DC-DC converter,- the duration of the period during which the current is being built-up in the inductor (TON) during a charge-discharge cycle,- the duration of the period TOFF during which the current is decreasing from IMAX to 0 in the inductor during a charge-discharge cycle.

[0040] Thanks to this embodiment, it is possible to refine the estimation of the energy being transferred according to the operating condition of the DC-DC converter. In discontinuous conduction mode, the energy transferred per charge-discharge cycle to the output of the DC- DC converter can be estimated as the duration of TOFF multiplied by the average current flowing to the output of the DC-DC converter and by the output voltage at the one or more output(s) of the DC-DC converter. This average current being itself calculated as half of the IMAX current, which is a function of the value of the inductor, of the voltage at the one or more input(s) of the DC-DC converter and potentially at the one or more output(s) of the DC-DC converter.

[0041] In another variant of the invention, the monitored inductive DC-DC converter operates in continuous and discontinuous mode, or the monitored inductive DC-DC converter is paired to a linear regulator and wherein the kinds of events counted by the activity monitoring circuit are:- the amount of charge and discharge cycles of the inductor when operating in discontinuous mode,- the enabling and disabling of the continuous mode,- a plurality of different events EVENTi corresponding to the expiration of a unit delay DUNIT without exiting the continuous mode when in continuous mode and for which the average current exiting or entering the DC-DC converter is .

[0042] When a large power range, typically from below lOmW to more than lOOmW, is expected to be transferred by the DC-DC converter, a mixed mode between continuous conduction mode or use of a linear regulator and discontinuous conduction mode has the best power efficiency. Such large power range might occur for instance when harvesting energy from a photovoltaic cell that is exposed to either indoor or outdoor lighting or when delivering energy to an electronic load that operates in different power modes such as a microcontroller that can be in deep sleep, sleep or active states, or an electronic load that has different workloads such as a wireless communication means that is idle or that actively performs a wireless communication or such as a sensor that is idle or that performs a sensing operation. Counting different kinds of events according to the operating condition of the DC-DC converter allows refining the estimate EEST of the energy being transferred to the DC-DC converter bytaking into account the operating mode of the DC-DC converter and the transition of one operating mode to the other.

[0043] In yet another variant, the one or more parameter(s) Ei, Ej,... Exare a function of the following parameters when the DC-DC converter operates in continuous mode or when a companion linear regulator is used:- the one or more input voltage(s) of the DC-DC converter (2), and / or the one or more output voltage(s) of the DC-DC converter (2),- the average current flowing through the inductor (20), or through the input(s) (21) or through the output(s) (22) of the DC-DC converter (2) or of the linear regulator.- the duration of DUNIT, and are a function of the at least three of the following parameters when the DC-DC converter operates in discontinuous mode:- the one or more input voltage(s) of the DC-DC converter (2),- the one or more output voltage(s) of the DC-DC converter (2),- the peak current IMAX reached in the inductor (20),- the size of the inductor (20) used as the reactive component of the DC-DC converter (2),- the duration TON of the period during which the current is being built-up in the inductor (20) during a charge-discharge cycle,- the duration TOFF of the period during which the current is decreasing from IMAX to 0 in the inductor (20) during a charge-discharge cycle.

[0044] Thanks to this embodiment, it is possible to refine the estimation of the energy being transferred according to the operating condition of the DC-DC converter. For instance, when operating in continuous conduction mode or when using the companion linear regulator, the energy transferred to the output (from the input) of the DC-DC converter can be estimated as the average current during a delay DUNIT multiplied by the output voltage (input voltage) of the DC-DC converter and by the duration of the delay DUNIT-

[0045] In a different embodiment of the invention at least one of the DC-DC converter(s) is a switched-capacitor converter using one or more capacitor(s) as the reactive component(s).

[0046] Switched capacitor converters have the advantage of being easily integrated into the same integrated circuit as the electronic load being supplied. Further capacitors used as reactive components can also be integrated to the same integrated circuit or be implemented by passive components that are cheaper than inductors.

[0047] In that case, preferably, the events counted by the activity monitoring circuit are the amount of charge / discharge cycles of the capacitor(s) of the monitored switched-capacitor DC- DC converter.

[0048] Thanks to this embodiment, it is possible to refine the estimation of the energy being transferred by the DC-DC converter. The energy transferred during a charge / discharge cycle is afunction of the impedance of the DC-DC converter which is a function of the switching frequency of the DC-DC converter and thus of the number of charge-discharge cycle occurring during the monitoring period TMON that has a known duration.

[0049] Yet in that case, the one or more parameter(s) Ei, Ej,... Exare a function of the following parameters:- the one or more input voltage(s) of the DC-DC converter,- the one or more output voltage(s) of the DC-DC converter,- the voltage ratio(s) (m) between the no-load voltage(s) and the input voltage(s) of the DC-DC converter, wherein the no-load voltage is the voltage that would be obtained at the output(s) of the DC-DC converter when no current is drained at its output(s) and when its regulation loop is disabled,- a parameter that is a function of the size of the capacitor(s) used as the reactive component of the DC-DC converter and of the topology implemented by the power switches and the capacitor(s) of the DC-DC converter.

[0050] Thanks to this embodiment, it is possible to refine the estimation of the energy being transferred by the DC-DC converter. The energy transferred during a charge / discharge cycle is a function of the output voltage of the converter, of the difference between the output voltage and the no-load voltage and of the impedance of the converter. This impedance is itself a function of the size of the capacitor used as the reactive components of the DC-DC converter and of the topology implemented by the power switches and the capacitor(s) of the DC-DC converter, if the period between reconnection of the capacitors used as reactive components by the switched capacitor converter is long when compared to the time required to charge or discharge those capacitors.

[0051] In another embodiment, the one or more parameter(s) Ei, Ej,... Exare a function of the following parameters:- the one or more input voltage(s) of the DC-DC converter,- the one or more output voltage(s) of the DC-DC converter,- the impedance of the power switches implemented in the DC-DC converter,- a parameter that is a function of the topology implemented by the power switches and the capacitors (24) of the DC-DC converter.

[0052] Thanks to this embodiment, it is possible to refine the estimation of the energy being transferred by the DC-DC converter. The energy transferred during a charge / discharge cycle is a function of the output voltage of the converter, of the difference between the output voltage and the no-load voltage and of the impedance of the converter. This impedance is itself a function of the impedance of the power switches used to connect the capacitors used as reactive components of the DC-DC converter and of the topology implemented by the combination of the power switches and of the capacitor(s) of the DC-DC converter, if theperiod between reconnection of the capacitors used as reactive components by the switched capacitor converter is short when compared to the time required to charge or discharge those capacitors.

[0053] In advantageous cases, the one or more parameter(s) Ei, E2, ... Exare also a function of the efficiency of the DC-DC converter and / or of the temperature of the DC-DC converter.

[0054] Thanks to this embodiment, it is possible to refine the estimation of the energy being transferred by the DC-DC converter by tuning the former models according to the efficiency of the converter. Also, the temperature can influence the operation of the DC-DC converter, for instance by modifying the bias current used to define IMAX in a discontinuous inductive converter which as explained earlier has an impact on the energy transferred per charge / discharge cycle. The temperature can also alter the duration of unitary delay DUNIT or the duration of the time frame TMON during which the energy is being evaluated.

[0055] In a second aspect, the invention relates to a method for estimating the amount of energy transferred by an inductive DC-DC converter using an inductor (20) as reactive component and operating in discontinuous mode. According to this aspect of the invention, the method comprises the steps of:(i) starting a timer defining the time interval TMON in which the energy transferred by the DC-DC converter will be estimated,(ii) monitoring the activity of the DC-DC converter with an activity monitoring circuit by counting at least the amount of charge and discharge cycles of the inductor (20) occurring during TMON,(iii) once TMON is over, estimating the energy (EEST) that has been transferred by the DC-DC converter during TMON by:(iiia) selecting one parameter ESEU per kinds of events counted by the activity monitoring circuit amongst one or more parameter(s) Ei, E2,... Exthat are a representation of the amount of energy being provided at one or more input(s), or being delivered to one or more output(s) of the DC-DC converter per event counted by the activity monitoring circuit then(iiib) computing EEST by:- multiplying for each kind of event counted by the activity monitoring circuit, the selected parameter ESELI by the number of the corresponding kind of events counted by the activity monitoring circuit during TMON;- then by adding the different multiplication results together,(iv) saving EEST in a memory unit.

[0056] Preferably, ESELI is selected as a function of a numerical representation of the voltage(s) at the one or more input(s), and / or at the one or more output(s) of the DC-DC converter.

[0057] Then the input and output voltages can be used as the entries of a two-dimensional lookup table.

[0058] In another variant, the method comprises the additional step of (iiic) refining EEsTby multiplying it with a fitting parameter PFrr that is fixed for a given practical implementation of the DC-DC converter.

[0059] The PFIT parameter allows refining the estimation of the energy being transferred by the DC-DC converter according to the actual design of the system including the power monitoring system. This parameter PFIT is thus valid for a group of systems, or electronic devices that include a power monitoring system that shares the same design. For instance, the characteristics of the selected inductor such as its ESR can affect the efficiency of the DC-DC converter and thus the amount of energy transferred per counted events. The design of the PCB, on which the DC-DC converter is mounted, has a similar impact. The parameter PF|Tallows regrouping all those parameters influencing the estimation of the energy being transferred that are common for a single design.

[0060] In another variant, the method comprises the additional steps of:(ivb) after each step (iv), incrementing a counter ,(ivc) once the counter has reached a predefined value,(ivcl) change the value of an output signal at an output of the power monitoring system; and (ivc2) reset the counter. For example, to change the value of an output signal, a flag can be set to a predetermined value.

[0061] In another aspect, the invention relates to a method for calibrating the power monitoring system of the electronic device of the invention, the method comprises the steps of:- applying an input voltage and current to one of the one or more input(s) of the DC-DC converter,- measuring an actual output power POUT at one of the one or more output(s) of the DC-DC converter, which results in a known energy EOUT when integrated during a time TMON as defined by the timer as the duration of the time frame during which the amount of energy EEST is estimated,- reading the result EEST stored in the memory unit,- calculating a calibration factor ECAL as a ratio of the actual output energy EOUT to EEsTor as the ratio of POUT to EEST- The calibration factor ECAL can then be applied to the next estimations.

[0062] This method allows refining the value EEST according to parameters that influence the amount of energy transferred per event counted by the activity monitoring circuit that are specific for each individual system or electronic devices that use a power monitoring system. Examples of such parameters are the deviation of a bias voltage or current of a given integrated circuit, impacting the behavior of the monitored DC-DC converter, or the offset of sensorsimpacting the behavior of the power monitoring system. This alternative method is thus advantageous as the calibration is operated individually on each system or electronic device individually and can be used to refine the value of EEST of each system or electronic device individually as opposed to the parameter PFIT described here above that applies to all systems or electronic devices that share a common design. Calculating ECAL by performing the ratio of EQUT to EEST allows calibrating the energy being transferred while calculating ECAL by performing the ratio of POUT to EEST is useful when the user wants to extract an image of the power being transferred in average during the time frame TMON during which the amount of energy EEST is estimated.

[0063] In a variant of the calibration method offering similar advantages, the method comprises the steps of:- applying a load at one of the one or more output(s) of the DC-DC converter,- measuring an actual input power PIN, which results in a known energy EIN when integrated during a time TMON as defined by the timer as the duration of the time frame during which the amount of energy EEST is estimated,- reading the result EEST stored in the storage means,- calculating a calibration factor ECAL as a ratio of the actual input energy EIN to EEST or as the ratio of PIN to EEST- The calibration factor ECAL can then be applied to the next estimations.

[0064] Another aspect of the invention concerns a method for automatically calibrating the power monitoring system of the electronic device of the invention.

[0065] According to the invention, this method comprises the steps of:- disconnecting one of the one or more input(s) of the DC-DC converter from an energy source,- providing a known power to one of the one or more input(s) of the DC-DC converter, resulting to a known power POUT being delivered to one of the one or more output(s) of the DC-DC converter, which results in a known energy EQUT when integrated during a time TMON as defined by the timer as the duration of the time frame during which the amount of energy EEST is estimated,- configure the DC-DC converter to select the input where the power is provided,- configure the DC-DC converter to select an output amongst its one or more output(s),- operating the DC-DC converter,- using the power monitoring system to estimate EEST, the amount of energy being transferred during TMON to the selected output from the selected input with the method above described,- calculating a calibration parameter ECAL as the ratio of EQUT to EEST or as the ratio of POUT to EEST- The calibration factor ECAL can then be applied to the next estimations.

[0066] In this method, a known current or power is provided to the input(s) while the DC-DC converter is configured to regulate its input voltage(s) at a known value.

[0067] POUT can be evaluated from PIN as POUT equals to PIN multiplied by the converter efficiency and where the efficiency might be or not a function of the input voltage, output voltage, output current and or the temperature.

[0068] The advantage of an auto-calibration process is that there is no need for the user to perform manually the calibration steps and that the calibration can periodically be performed in order to take into account the impact of parameters evolving slowly in time such as the aging of the component or the ambient temperature.

[0069] In a variant of the automatic calibration method offering similar advantages, the method comprises the steps of :- disconnecting one of the one or more output(s) of the DC-DC converter from the load(s) connected to it, or configuring the load(s) connected to it so that its power consumption becomes minimum or known,- applying a known load to one of the one or more output(s) of the DC-DC converter, resulting to a known power Pin being provided by one of the one or more input(s) of the DC-DC converter which results in a known energy EIN when integrated during a time TMON as defined by the timer as the duration of the time frame during which the amount of energy EEST is estimated,-configure the DC-DC converter to select an input amongst its one or more input(s), -configure the DC-DC converter to select the output where the known load is applied and to regulate this output at a known voltage,- operating the DC-DC converter,- using the power monitoring system to estimate EEST, the amount of energy being transferred during TMON from the selected input to the selected output with the method above described,- calculating a calibration parameter ECAL as the ratio of EIN to EEST or as the ratio of PIN to EEST- The calibration factor ECAL can then be applied to the next estimations.

[0070] In a preferred embodiment, a plurality of measured energy values EEST are averaged to obtain an averaged energy measurement EESTAVG for use in calculating the calibration factor ECAL-. The calibration factor ECAL- can then be applied to the next estimations.

[0071] Performing the calibration based on an averaging EESTAVG of a plurality of measured energy EEST allows a better accuracy of this calibration as the average value of some parameters influencing the control of the DC-DC converter, such as its supply voltage, or control inputs that are updated periodically are captured over longer periods.

[0072] Any of the calibration method detailed above can be refined by measuring the ratio between the actual TMON generated by the power monitoring system and the theoretical TMON used to evaluate the parameters EIN, EOUT, PIN or POUT to perform the calibration and by multiplying the parameters ECAL or ECAL- by this ratio.

[0073] The parameter PFIT, ECAL or ECAL- can be stored in a memory within the logic controller (12) so that it can access those parameters to refine the measured energy estimate EEST before storing it into the memory (14).

[0074] Alternatively, those parameters can be saved within the application that includes a device featuring power monitoring system described in this invention, and the correction of the energy estimate EEST can be performed by another circuit or software of the application.

[0075] Brief description of the figures

[0076] Embodiments of the invention will now be presented with reference to the appended figures. Said embodiments and figures have no other purpose than illustrating embodiments of the invention and have no limiting function.

[0077] Fig. 1 to 5 are schematic representations of electronic devices according to the invention.

[0078] Detailed description of an embodiment of the invention

[0079] Figure 1 describes an electronic device that is typically incorporated into fitness trackers, smartwatches, or medical implants.

[0080] This electronic device (0) is made of a combination of a power monitoring system (1) and a DC-DC converter (2) capable of transferring energy from various energy sources, including but not limited to a battery, a rechargeable battery, a supercapacitor, a power rail output from another power converter, or a renewable energy source such as a photovoltaic cell, a piezoelectric generator, an RF antenna (or the output of a rectifier connected in series with the RF antenna), or a thermoelectric generator.

[0081] The power monitoring system (1) is an electronic system designed to monitor the amount of energy transferred by one or more DC-DC converter(s) (2). The power monitoring system and its subcomponents can be integrated into a single integrated circuit or constructed from multiple components on different circuits. The power monitoring system can be integrated within the same integrated circuit as the DC-DC converter (2), or it can be incorporated into a different integrated circuit.

[0082] The DC-DC converter (2) can be an inductive switching regulator operating in discontinuous mode or in continuous and discontinuous mode or a combination of both an inductive converter operating in discontinuous mode and a linear regulator with the switching from one converter to the other depending on the status of the system (start-up or regular operation), the actual current being supplied to the load, or on the voltage difference between the input and output of the converter. This converter can have multiple inputs or outputs .

[0083] For example, the converter can employ techniques such as inductance sharing to manage multiple inputs and / or outputs.

[0084] In another example, the switching inductive converters handle multiple inputs (21) and / or outputs (22) by operating in discontinuous mode and by using an input(s) and / or output(s) selection switch matrix.

[0085] In discontinuous conduction mode, energy is transferred from an input to an output through a cycle of charging and discharging of the inductor (20) used as a reactive component. This cycle is characterized by the energy in the inductor being zero or nearly zero at the beginning and end of the cycle. By selecting a combination of inputs and outputs for each cycle using a switch matrix at the input(s) and / or output(s) of the DC-DC converter, it is possible to manage multiple inputs and / or outputs. For input selection, this switch matrix can be placed either between the inputs of the DC-DC converter (2) and the power switch controlling the charge / discharge cycle of the inductor (20) or be part of the power switch itself. In the latter case, the switches have two functions: selecting the input and connecting the inductor (20) as part of a charge / discharge cycle. The same principle applies to the selection of the outputs of the DC-DC converter (2): a switch matrix can be placed either between the outputs of the DC- DC converter and the power switch controlling the charge / discharge cycle of the inductor (20) or be part of the power switch itself. In the latter case, the switches have two functions: selecting the output and connecting the inductor (20) as part of a charge / discharge cycle.

[0086] The power monitoring system (1) comprises several sub-blocks. A timer (13) sets a period TMON during which the energy is monitored. This timer can be implemented, for instance, as a counter that counts clock cycles and defines TMON as the time required to count a predetermined number of clock cycles. Alternatively, TMON can be generated by a clock divider that creates a time period TMON based on a subdivision of an existing clock. Alternatively, TMON can be defined using the relaxation time of a circuit composed of a capacitor and a current limiting device such as a resistor. It is also possible to use a timer from a peripheral of an integrated circuit, such as a microcontroller.

[0087] The timer (13) is preconfigured to reset itself so that when the period TMON is over, a new period begins. This new period is associated with a new evaluation of the energy being transferred by the DC-DC converter (2).

[0088] The activity monitoring circuit (11) is a circuit that monitors the DC-DC converter (2) and provides a numerical representation of its activity and consists in a counter made of logic cells that increments each time a charge-discharge cycle occurs in the DC-DC converter. In this case, the DC-DC must be able to generate a logic signal each time it performs a chargedischarge cycle.

[0089] The activity monitoring can be configured to count the number of cycles occurring for a given peak current being charged in the inductor. For instance, if the DC-DC converter is configured to charge the inductor up to a current of 100mA, 200mA, or 300mA, the activity monitoring circuit could count the number of cycles where the inductor (20) has been chargedup to 100mA, the number of cycles where it has been charged up to 200mA, and the number of cycles where it has been charged up to 300mA in different counters and provides the different count results to the logic controller (12).

[0090] The output value of the monitoring circuit is stored in a memory (14). This value can take different forms such as the result of the monitoring circuit over one monitoring window, the accumulation of results of the monitoring circuit over a predefined number of monitoring windows, or an average of results of the monitoring circuit over a predefined number of monitoring windows .

[0091] The memory (14) is, for instance, built with a non-volatile memory such as flash memory, or volatile memories such as random-access memory (SRAM), or registers.

[0092] The output of the monitoring system (15) can be a general purpose input / output (GPIO), a signal driven at a logical 1 or 0, an open drain access terminal that is left floating or connected to a logical 0 or 1, an Interrupt Request (IRQ) which raises a flag when data or consolidated data from the power monitoring system are available, or a register value that changes and is provided through a communication means such as I2C, SPI, or UART.

[0093] The logic controller (12) can be implemented by a combinatory circuit forming a hardware accelerator or by a software program compiled into an FPGA or any other programmable circuit, such as a microcontroller, a microprocessor, or a processor.

[0094] The logic controller (12) includes several subparts, such as a means to evaluate and select the parameters Ei, E2, ... Ex, which represents the energy transferred per counted event. A convenient means to evaluate and select these parameters is the use of a lookup table (121) that stores precomputed values of these parameters according to a multidimensional table. This table has one or several dimensions corresponding to parameters fluctuating during the operation of the DC-DC converter (2) and influencing the amount of energy transferred per event counted by the activity monitoring circuit. The logic controller (12) can also contain a second memory unit (124) for use in a calibration method as will be explained hereunder.

[0095] For instance, if the converter (2) is an inductive switching converter that boosts the input voltage to a higher value and operates in discontinuous mode, the energy transferred by the converter to an output can be estimated by IOUT times VOUT times TOFF, where IOUT is the average current delivered to this output, VOUT is the average voltage at this output, and TOFF is the time required for the inductor to deliver the charges accumulated in the inductor to the output. The average current delivered to the output can itself be a function of the input voltage or of the peak current that is flowing in the inductor when switching from the charging phase to the discharging phase. The lookup table (121) could thus use input parameters such as peak currents, input voltage, and / or output voltage.

[0096] Figure 2 shows another electronic device (0) with a DC-DC converter (2) and a power monitoring system (1) comprising a controller (12) with other means to evaluate and selectthose parameters Ei, E2, ...Exthat consist in using a combinatory circuit or hardware accelerators (122) that, by performing arithmetic operations from the inputs relevant for the evaluation of the energy being transferred per charge-discharge cycle, can evaluate the value of those parameters. This is a more practical approach, requiring a lower silicon area if the size of the lookup table increases too much because of a high number of entries.

[0097] The controller (12) is configured to evaluate the amount of energy being transferred by the DC-DC converter (2) by multiplying, for each kind of event counted by the activity monitoring circuit (11), the result of the count associated with this kind of event by one of the parameters Ei, E2, ...Exand by summing each multiplication.

[0098] For instance, if the DC-DC converter is an inductive switching converter operating in discontinuous mode and if the activity monitoring circuits counted Ni cycles where the inductor (20) has been charged up to 100mA, N2cycles where it has been charged up to 200mA, and N3 cycles where it has been charged up to 300mA, and if the associated parameters Ei, E2, ... Exare respectively Ei, E2, and E3, the result of the power monitoring system would be equal to Ni times Ei + N2times E2+ N3 times E3.

[0099] Parameters useful for the evaluation of Ei, E2, ... Exby the logic controller (12) can be evaluated by the power monitoring system (1) itself, provided by other circuits, or deduced from the system configurations.

[0100] For instance, the peak current in the inductor (20) when switching from the charging phase to the discharging phase can be preconfigured and monitored by means of a current monitoring circuit. In this case, the theoretical value of this peak current is known by the system and can be used for the evaluation of the transferred energy per cycle.

[0101] In another example, the output voltage of the system can be preconfigured so that the converter (2) regulates its output voltage at a preconfigured value that is known and can be used in a similar way for the evaluation of the energy transferred by the converter (2).

[0102] In a further example, the input voltage of the converter (2) is known as it is set by a maximum power point tracker module that evaluates and sets the target input voltage of a DC- DC converter (2) extracting energy from a renewable energy source such as a PV cell. This target input voltage is set to adjust the bias voltage of the source to maximize the amount of power provided by the source.

[0103] Figures 1, 2, and 3 show embodiments where the power monitoring system (1) evaluates the relevant information about the input and output voltages using voltmeters (16) and / or (17). These voltmeters measure the actual input (21) and / or output (22) voltage(s) of the DC-DC converter (2). They can, for instance, be implemented by means of an analog-to- digital converter (ADC). This ADC can be duplicated or preferably have multiple channels so that the same ADC can be reused to monitor one or more input(s) (21) and one or more output(s) (22) of one or more DC-DC converter(s) (2).

[0104] Similar to other blocks, the ADC can be integrated into the same integrated circuit as the other parts of the power monitoring system, or it can be provided by another circuit such as a microcontroller that has an ADC as an available peripheral.

[0105] Figure 2 shows another way to obtain information relevant for the evaluation of the parameters Ei, Ej... Exby using a current sensing circuit (19), for example with the ammeters (19A) and (19B) that measure the actual input and / or output current(s) flowing in or from the DC-DC converter (2). These ammeters can be built, for instance, from replicas of the power device in the current flow path through the DC-DC converter. The voltage across these replicas can be measured, and the amount of current flowing through the DC-DC converter (2) can be deduced from this voltage measurement. This voltage measurement can be performed, for instance, using an ADC as described above. The voltage across such replicas can also be compared to predefined thresholds using voltage comparators that compare the voltage on the replica to voltage references, with each voltage reference corresponding to a current threshold flowing through the DC-DC converter (2).

[0106] In an embodiment shown in Figure 3, the controller (12) includes, beside the lookup table (121), a counter (125) that is incremented each time an estimate of the transferred energy EEST is available. It allows the logic controller (12) to perform an operation on these results once the counter (125) has reached a predetermined value. The operation performed by the logic controller (12) can, for instance, be an addition to evaluate the total energy being transferred by the DC-DC converter (2) over a period longer than TMON, or an averaging to provide an image of the average power being transferred during a period longer than TMON-

[0107] By reading only the results of this operation, another circuit retrieving the information from the power monitoring system (1) would consume less energy due to reduced wakeups for communication.

[0108] In an embodiment illustrated in Figure 4, the electronic device (0) includes several DC- DC converters (2i, 2i> 3i, 3j) transferring and / or using energy from a storage device (4) to deliver energy to one or several loads. In this embodiment, the power monitoring system (1) monitors the net energy flow in the storage device (4) based on the aggregation of the energy flow evaluations occurring in each DC-DC converter (2i, h, 3i, 3j).

[0109] An example of an application taking advantage of this embodiment is a system supplied by two PV cells with a first DC-DC converter (2i) connected between the first PV cell and a storage device, and a second DC-DC converter (2j) connected between the second PV cell and the storage device, while several DC-DC converters (3i), (3j) are used to deliver energy to circuits such as a sensor, a microcontroller, or a wireless communication means. In this example, the power monitoring system (1) can deliver information about the energy flow in each converter individually or the result of the net energy flow evaluation in the storage device (4), allowing the system to know whether the storage device (4) is being charged by the PVcells through converters (2i) and (2j) or if it is being discharged due to the consumption of the other circuits connected to converters (3i), (32).

[0110] In another embodiment that is not depicted in the figures, the result of the power monitoring system (1) can be adjusted using a fitting parameter common to all devices sharing a common design. Indeed, the evaluation of parameters Ei, E2...EXis performed based on several assumptions about the system. For instance, it can consider a given efficiency of the converter (2) that is impacted by the actual design of the system, such as the selection of the inductor (20) and its equivalent series resistor, or the design of the power path on the PCB. The real impact of such parameters specific to a particular design can be taken into account using the fitting parameter PFIT- The value of the estimated energy EEST can then be refined by multiplying it with the parameter PFIT-

[0111] In a further embodiment, the result of the power monitoring system can be selfcalibrated. To perform this self-calibration, the DC-DC converter (2) is disconnected from its input (21) or output (22). Alternatively the load connected to the output(22) is set in a mode where its consumption is negligeable or where it is known. This disconnection or reconfiguration of the load is performed while the calibration process is ongoing so that the energy provided by the input (21) or taken by the output (22) does not perturb the calibration operation.

[0112] For instance, if the DC-DC converter (2) is extracting energy from a renewable energy source to store it in a storage device (4), the energy source will be disconnected during the calibration process. In another example, if the DC-DC converter (2) is connected between a storage device (4) and an application load such as a sensor, a microcontroller, or a wireless communication means, the application load will be disconnected or set in a mode where its consumption is negligible during the calibration process.

[0113] The disconnection or reconfiguration of the application load is activated by one or more digital signal(s) (123b), as illustrated in Figure 3, provided by the logic controller (12). This digital signal can, for instance, control a power switch in the power path between the energy source and the input (21) of the DC-DC converter (2) or between the application load and the output (22) of the DC-DC converter (2).

[0114] If the DC-DC converter (2) has been disconnected from its regular input, an alternative energy source will be connected during the calibration process. This alternative energy source is typically a current of a known value (18a) that is applied to the DC-DC converter (2) input while the voltage of this input is fixed at a known voltage. The known current source (18a) can be obtained by using a current reference or by applying a resistor between two known voltages, such as for instance the input (21) and output (22) voltage of the DC-DC converter (2). The known voltage value can be obtained by forcing the operation of the DC-DC converter (2) so that its input voltage is regulated to the target known voltage while the output voltage ismeasured and connected to a device that has a voltage that does not vary during the calibration period, such as for instance a Li-ion battery.

[0115] Alternatively, as illustrated in Figure 3, if the DC-DC converter (2) has been disconnected from its regular output, a known load (18b) will be applied instead. The known load can be applied to the output by connecting a resistor of a known value between the output of the DC-DC (2) converter and the ground or by connecting a current sink of a known value generated by a current reference to the output of the DC-DC converter (2). Similar to the previous paragraph, the power delivered to the output of the DC-DC converter (2) is known if the voltage at the output of the DC-DC converter (2) is known as well as the load connected to it. The voltage at the output can be known as the target regulation voltage of the DC-DC converter (2).

[0116] To perform the auto-calibration, the power monitoring system evaluates the amount of power being transferred under the conditions described above. The result of this evaluation is compared to expected values that represent the anticipated amount of energy being transferred for a known input energy source or a known load. These values are stored in the logic controller in a second memory unit (124). The result of this comparison allows determining a calibration factor ECAL that can be applied to subsequent results of the power monitoring system. Therefore, the parameter ECAL, once calculated, is stored in a third memory within the logic controller.

[0117] This auto-calibration can be performed once or several times during the operation of the system to compensate for slowly evolving parameters influencing the behavior of the DC- DC converter (2), such as aging effects degrading the impedance of the power transistor or power tracks, or temperature impacts on the efficiency of the DC-DC converter (2).

[0118] Alternatively, this auto-calibration can be performed by comparing the result of the power monitoring system obtained during the calibration process to values that represent the expected amount of power being transferred for a known input power source or a known load, which are stored in the logic controller in a second memory unit (124). The result of this comparison allows for determining a calibration factor ECAL that can be applied to subsequent results of the power monitoring system. In this case, the output of the power monitoring system becomes a representation of the average power that has been transferred through the DC-DC converter (2) over the evaluation period TMON-

[0119] Figure 5 shows another electronic device (0) configured in a different manner for performing an autocalibration method. In the embodiment of Figure 5, a power monitoring system (1) for monitoring energy transfer in a DC-DC converter (2) is provided. This power monitoring system (1) comprises a circuit (18a) configured to provide a known current IREF to an input (21) of the DC-DC converter (2). The logic controller (12) includes a second memory unit (124) configured to store the expected results of the power monitoring system (1) conversiondepending on the input voltage(s) of the DC-DC converter (2) and on the known current lREF. The logic controller (12) is further configured to provide a target regulation voltage to the input (21) of the DC-DC converter (2) where the known current lREFis provided, and to provide a control signal (123) to disconnect the one or more input path(s) between the energy source and the input (21) of the DC-DC converter (2) where the known current lREFis provided.

[0120] Figure 5 further illustrates the monitored DC-DC converter (2) is a switched-capacitor converter using one capacitor (20) as reactive component. It must be understood that this feature is not inextricably linked to the described auto-calibration method.List of the drawing references:0 Electronic device1 Power monitoring system2 DC-DC converter2i DC-DC converter3i DC-DC converter4 Storage device11 Activity monitoring circuit12 Logic controller121 Lookup table122 Combinatory circuit123 Control signal123b Control signal124 Second memory unit125 Counter13 Timer14 memory unit15 Output of the power monitoring system16 Voltmeter17 Voltmeter18a and 18b Circuits configured to provide a known current19 Current sensing circuit19A Ammeter19B Ammeter20 Inductor21 Input of a DC-DC converter21i Input of a DC-DC converter22 Output of a DC-DC converter22i Output of a DC-DC converterCapacitorInput of a DC-DC converterOutput of a DC-DC converter

Claims

24Claims1. An electronic device (0) comprising- one or more inductive DC-DC converter(s) (2) configured to transfer energy from one or more input(s) (21) to one or more output(s) (22), wherein at least one of the DC-DC converter(s) (2) is an inductive converter using an inductor (20) as reactive component and operates in discontinuous mode and is configured to stop the charging of the inductor (20) when a current IMAX has been accumulated in the inductor (20),- a power monitoring system (1) for estimating the amount of energy ( EEST) being provided at one or more input(s) (21) or being delivered to one or more output(s) (22) of the DC-DC converter(s) (2), the power monitoring system (1) comprising:- an activity monitoring circuit (11) configured to count at least the amount of charge and discharge cycles of the inductor (20) and providing one or more count result(s),- a logic controller (12) configured to estimate periodically the amount of energy EEST based on i) the activity monitoring circuit (11) count result(s), and ii) one or more parameter(s) Ei, Ej,... Exthat are a representation of the amount of energy being provided at one or more input(s) (21), or being delivered to one or more output(s) (22) of the DC-DC converter (2) per event counted by the activity monitoring circuit (11),- a timer (13) configured to set the duration of the time frame TMON during which the amount of energy EEST is estimated by the logic controller (12), in order to provide periodic results over consecutive time frames,- a memory unit (14) configured to store the results of the periodic estimations.

2. An electronic device (0) according to claim 1 wherein the memory unit (14) is configured to store one or more result(s) and to output a signal at an output (15) of the power monitoring system (1) when a preconfigured number N of results are available.

3. An electronic device (0) according to claim 2 wherein the logic controller (12) is configured to perform a logic operation on the results stored into the memory unit (14) when the preconfigured number N of results are available and to store the results of this logic operation in the memory unit (14) wherein the logic operation is an evaluation of the average value of the stored results or the addition of the values of the stored results.

4. An electronic device (0) according to any one of the claim 1 to 3, further comprising a first voltmeter (16) configured to provide numerical representations of the inputvoltage(s) of the DC-DC converter (2) to the logic controller (12), or a second voltmeter (17) to provide numerical representations of the output voltage(s) of the DC-DC converter (2) to the logic controller (12) or two voltmeters (16-17) configured to provide numerical representations of the input and output voltages of the DC-DC converter (2) to the logic controller (12).

5. An electronic device (0) according to any one of the claim 1 to 4, further comprising an ammeter (19A) configured to provide numerical representations of the input current(s) of the DC-DC converter (2) to the logic controller (12), or an ammeter (19B) configured to provide numerical representations of the output current(s) of the DC-DC converter (2) to the logic controller (12) or two ammeters (19A-19B) configured to provide numerical representations of the input and output current(s) of the DC-DC converter (2) to the logic controller (12).

6. An electronic device (0) according to any one of the claims 1 to 5, wherein parameters Ei, Ej, ... Exare stored in a lookup table (121) which is part of the logic controller (12).

7. An electronic device (0) according to any one of the claims 1 to 5, wherein parameters Ei, Ej, ... Exare computed by the logic controller (12) with a logic function implemented by combinatory circuits (122) or a program.

8. An electronic device (0) according to any one of the claims 1 to 7, wherein the duration set by the timer (13) is either fixed or dynamically controlled by the logic controller (12).

9. An electronic device (0) according to any one of the claims 1 to 8, wherein the logic controller (12) is configured to perform a calibration process of the power monitoring system (1).

10. An electronic device (0) according to claim 9, wherein the logic controller (12) is configured to perform an auto-calibration process of the power monitoring system (1).

11. An electronic device (0) for monitoring energy transfer in a DC-DC converter (2), according to claim 10, comprising:- a circuit (18a) configured to provide a known current IREF to one or more of the input(s) of the DC-DC converter (2) wherein the logic controller (12) includes a second memory unit (124) configured to store the expected results of the power monitoring system (1) conversion depending on the one or more input voltage(s) of the DC-DC converter (2) and on the known current IREF and, optionally, on the one or more output voltage(s) of the DC-DC converter (2). wherein the logic controller (12) is further configured to:- provide a target regulation voltage to the one or more input(s) of the DC-DC converter (2) where the known current IREF is provided, and- provide a control signal (123) to disconnect the one or more input path(s) between the energy source and the one or more input(s) of the DC-DC converter (2) where the known current IREF is provided.

12. An electronic device (0) for monitoring energy transfer in a DC-DC converter (2), according to claim 10, comprising:- a current sink (18b) sinking a known current IREFB from one or more of the output(s) of the DC-DC converter (2), wherein the logic controller (12) includes a second memory unit (124) configured to store the expected results of the power monitoring system (1) conversion depending on the one or more output voltage(s) of the DC-DC converter (2) and on the known current IREFB and optionally on the one or more input voltage(s) of the DC-DC converter (2) and wherein the logic controller (12) is further configured to- provide a target regulation voltage to the one or more output(s) of the DC-DC converter (2) where the known current IREFB is sunk and to- provide a control signal (123b) to disconnect the one or more output path(s) between electronic load(s) and the one or more output(s) of the DC-DC converter (2) where the known current IREFB is sunk or to put the electronic load(s) in a state where their consumption is minimum or known.

13. An electronic device (0) according to any one of the claims 1 to 12, comprising:- at least one DC-DC converter(s) (2i) configured to transfer energy from one or more input(s) (21i) to one or more output(s) (22i),- at least one DC-DC converter(s) (3i) configured to transfer energy from one or more input(s) (31i) to one or more output(s) (32i),- a storage device (4) connected to at least one of the one or more output(s) (22i) and to at least one of the one or more input(s) (31i),-electronic loads connected to at least one of the one or more output(s) (32i) or (22i), wherein the power monitoring system (1) monitors the net energy transfer in or from the storage device (4).

14. An electronic device (0) according to any one of the claims 1 to 13 wherein IMAX is either predetermined or dynamically adjusted by the logic controller (12)15. An electronic device (0) according to any one of the claims 1 to 14, wherein the one or more parameter(s) Ei, Ej,... Exare a function of at least three parameters amongst the following parameters:T1- the one or more input voltage(s) of the DC-DC converter (2),- the one or more output voltage(s) of the DC-DC converter (2),- the peak current IMAX reached in the inductor (20),- the size of the inductor (20) used as the reactive component of the DC-DC converter (2),- the duration of the period during which the current is being built-up in the inductor (20) during a charge-discharge cycle (TON),- the duration of the period during which the current is decreasing from IMAX to 0 in the inductor (20) during a charge-discharge cycle (TOFF).

16. An electronic device (0) according to claim 15 wherein the monitored inductive DC-DC converter (2) operates in continuous and discontinuous mode and wherein the kinds of events counted by the activity monitoring circuit (11) are:- the amount of charge and discharge cycles of the inductor (20) when operating in discontinuous mode,- the enabling and disabling of the continuous mode,- a plurality of different events EVENTi corresponding to the expiration of a unit delay DUNIT without exiting the continuous mode when in continuous mode and for which the average current exiting or entering the DC-DC converter is in the range .

17. An electronic device (0) according to claim 15 wherein the monitored inductive DC-DC converter (2) operates in discontinuous mode and is paired to a linear regulator and wherein the linear regulator and the DC-DC converter(2) are not enabled simultaneously and wherein the kinds of events counted by the activity monitoring circuit (11) are:- the amount of charge and discharge cycles of the inductor (20) when operating in discontinuous mode,- the enabling and disabling of the linear regulator,- a plurality of different events EVENTi corresponding to the expiration of a unit delay DUNIT without exiting disabling the linear regulator once enabled and for which the average current exiting or entering the DC-DC converter is in the range .

18. An electronic device (0) according to any one of the claims 1 to 17, wherein a current sensing circuit (19) measures the current flowing through the inductor (20) or at the input or at the output of the DC-DC converter (2) and provides a numerical representation of this current.

19. An electronic device (0) according to the claim 16, wherein the one or more parameter(s) Ei, Ej,... Exare a function of the following parameters when the DC-DC converter (2) operates in continuous mode:28- the one or more input voltage(s) of the DC-DC converter (2) and / or the one or more output voltage(s) of the DC-DC converter (2),- the average current flowing through the inductor (20) or at the input(s) (21) or at the output(s) (22) of the DC-DC converter (2),- the duration of DUNIT of the activity monitoring circuit (11), and are a function of the at least three of the following parameters when the DC-DC converter (2) operates in discontinuous mode:- the one or more input voltage(s) of the DC-DC converter (2),- the one or more output voltage(s) of the DC-DC converter (2),- the peak current IMAX reached in the inductor (20),- the size of the inductor (20) used as the reactive component of the DC-DC converter (2),- the duration TON of the period during which the current is being built-up in the inductor(20) during a charge-discharge cycle,- the duration TOFF of the period during which the current is decreasing from IMAX to 0 in the inductor (20) during a charge-discharge cycle.

20. An electronic device (0) according to the claim 17, wherein the one or more parameter(s) Ei, Ej,... Exare a function of the following parameters when the paired linear regulator is enabled and when the inductive converter operating in discontinuous mode is desabled:- the one or more input voltage(s) of the DC-DC converter (2) and / or the one or more output voltage(s) of the DC-DC converter (2),- the average current flowing through the paired linear regulator or at its input or at its output,- the duration of DUNIT of the activity monitoring circuit (11), and are a function of the at least three of the following parameters when the DC-DC converter (2) operates in discontinuous mode and when the paired linear regulator is desabled:- the one or more input voltage(s) of the DC-DC converter (2),- the one or more output voltage(s) of the DC-DC converter (2),- the peak current IMAX reached in the inductor (20),- the size of the inductor (20) used as the reactive component of the DC-DC converter (2),- the duration TON of the period during which the current is being built-up in the inductor (20) during a charge-discharge cycle,- the duration TOFF of the period during which the current is decreasing from IMAX to 0 in the inductor (20) during a charge-discharge cycle.2921. An electronic device (0) according to claim 15, 19 or 20, wherein the one or more parameter(s) Ei, Ej... Exare also a function of the efficiency of the DC-DC converter (2) and / or of the temperature of the DC-DC converter (2).

22. A method for estimating the amount of energy transferred by an inductive DC-DC converter (2) using an inductor (20) as reactive component and operating in discontinuous mode comprising the steps of:(i) starting a timer (13) defining the time interval (TMON) in which the energy transferred by the DC-DC converter (2) will be estimated,(ii) monitoring the activity of the DC-DC converter (2) with an activity monitoring circuit (11) by counting at least the amount of charge and discharge cycles of the inductor (20) occurring during TMON,(iii) once TMON is over, estimating the energy (EEST) being transferred by the DC-DC converter (2) by:(iiia) selecting one parameter ESEU per kind of events counted by the activity monitoring circuit (11) amongst one or more parameter(s) Ei, Ej,... Exthat are a representation of the amount of energy being provided at one or more input(s) (21), or being delivered to one or more output(s) (22) of the DC-DC converter (2) per event counted by the activity monitoring circuit (11) then,(iiib) computing EEST by:- multiplying for each kind of event counted by the activity monitoring circuit (11), the selected parameter ESELI by the number of the corresponding kind of events counted by the activity monitoring circuit (11) during TMON,- then by adding the different multiplication results together,(iv) saving EEST in a memory unit (14).

23. The method of claim 22 wherein ESELI is selected as a function of a numerical representation of the one or more input voltage(s), and / or at the one or more output(s) (22) of the DC-DC converter (2).

24. The method of claim 22 or 23 with the additional step of(iiic) refining EEST by multiplying it with a fitting parameter PFIT that is fixed for a given practical implementation of the DC-DC converter (2).

25. The method of any of the claims 22 to 24 with the additional steps of:(ivb) after each step (iv), incrementing a counter (125),(ivc) once the counter (125) has reached a predefined value:(ivcl) change the value of an output signal at an output (15) of the power30 monitoring system (1),(ivc2) reset the counter (125).

26. A method for calibrating the power monitoring system (1) as defined in claim 9, comprising the steps of:- applying an input voltage and current to one of the one or more input(s) of the DC-DC converter (2),- measuring an actual output power POUT at one of the one or more output(s) of the DC- DC converter (2), which results in a known energy EOUT when integrated during a time TMON as defined by the timer (13) as the duration of the time frame during which the amount of energy EEST is estimated,- reading the result EEST stored in the memory unit (14),- calculating a calibration factor ECAL as a ratio of the actual output energy EOUT to EEST or as the ratio of POUT to EEST-27. A method for calibrating the power monitoring system (1) as defined in claim 9, comprising the steps of:- applying a load at one of the one or more output(s) of the DC-DC converter (2),- measuring an actual input power PIN, which results in a known energy EIN when integrated during a time TMON as defined by the timer (13) as the duration of the time frame during which the amount of energy EEST is estimated,- reading the result EEST stored in the storage means (14),- calculating a calibration factor ECAL as a ratio of the actual input energy EIN to EEST or as the ratio of PIN to EEST-28. A method for automatically calibrating the power monitoring system (1) as defined in any of the claims 10 to 12, comprising the steps of:- disconnecting one of the one or more input(s) (21) of the DC-DC converter (2) from an energy source,- providing a known power to the previously disconnected input (21) of the DC-DC converter (2), resulting to a known power POUT being delivered to one of the one or more output(s) of the DC-DC converter (2), which results in a known energy EOUT when integrated during a time T ON as defined by the timer (13) as the duration of the time frame during which the amount of energy EEST is estimated,-configure the DC-DC converter (2) to select the input where the power is provided -configure the DC-DC converter (2) to select an output amongst its one or more output(s) (22),- operating the DC-DC converter (2),31- using the power monitoring system (1) to estimate EEST, the amount of energy being transferred during TMON from the input where the power is provided to the selected output with the method of anyone of the claims 30 to 33,- calculating a calibration parameter ECAL as the ratio of EQUT to EEST or as the ratio of POUT to EEST-29. A method for automatically calibrating the power monitoring system (1) as defined in any of the claims 10 to 12, comprising the steps of:- disconnecting one of the one or more output(s) (22) of the DC-DC converter (2) from its load(s) or putting the load(s) in a state where its consumption is minimum or known,- applying a known load to the previously disconnected output (22) of the of the DC-DC converter, resulting to a known power PIN being provided by one of the one or more input(s) of the DC-DC converter (2), which results in a known energy EIN when integrated during a time TMON as defined by the timer (13) as the duration of the time frame during which the amount of energy EEST is estimated,-configure the DC-DC converter (2) to select an input amongst its one or more input(s) (21),-configure the DC-DC converter (2) to select the output where the known load is applied and to regulate this output at a known voltage,- operating the DC-DC converter (2),- using the power monitoring system (1) to estimate EEST, the amount of energy being transferred during TMON from the selected input to the output where the known load is applied with the method of anyone of the claims 30 to 33,- calculating a calibration parameter ECAL as the ratio of EIN to EEST or as the ratio of PIN to EEST-30. A method according to any one of the claims from 26 to 29, wherein a plurality of measured energy values EEST are averaged to obtain an averaged energy measurement EESTAVG for use in calculating the calibration factor ECAL-.

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