Power supplies for integrated circuits

Abstract

An integrated circuit including a power supply portion (100), a battery connector (124) for connection to a battery, a boost portion (104) and an external connector (118). The power supply portion outputs a supply voltage to other parts of the integrated circuit. The boost portion includes a check portion (130) arranged to determine an impedance at the external connector. When the check portion determines that the impedance at the external connector is below a threshold impedance, it causes the boost portion to output a signal indicating that the supply voltage is ready. When the check portion determines that the impedance at the external connector is above the threshold impedance, it causes the boost portion to boost the supply voltage above the battery voltage and then output a signal indicating that the supply voltage is ready.

Description

[0001] 175425 / 01 FIR-2448

[0002] Power Supplies for Integrated Circuits TECHNICAL FIELD

[0003] This invention relates to the control of power being supplied during the operation of an integrated circuit (IC) device.

[0004] BACKGROUND

[0005] An IC is connected to a battery to provide power to it. In some circumstances the voltage of the battery can be different depending on how the IC is used. This is becoming more common as IC designs and functionality get ever more complicated as it enables a particular IC to be used in a variety of different applications.

[0006] The boot phase of a battery-powered IC device typically uses a module on the IC known as a hibernator, which is an always-on module which masters the device boot by interacting with associated regulators, biases and reset systems. Often, a higher supply voltage is required than can be provided by the battery. Thus, depending on the voltage of the attached battery, the battery voltage may need to be boosted to power-up the device. This is usually achieved using some form of a boost module, which starts when power is first supplied to the device, and indicates to the hibernator to continue the device boot when the boost module has boosted the supply voltage up to the required level. However, such an approach is not applicable if the battery voltage is already at the required supply voltage because a higher voltage battery is being used.

[0007] Thus, the IC may need to determine if a boost to the supply voltage is required. This can in theory be achieved by measuring the battery voltage, however this can be difficult to do during start-up when most systems are not available. The present invention aims to address this problem.

[0008] SUMMARY

[0009] From a first aspect, the invention provides an integrated circuit including a power supply portion the power supply portion comprising battery connector for connection to a battery having a battery voltage, a boost portion and a further external connector;wherein the power supply portion is arranged to output a supply voltage to other parts of the integrated circuit;

[0010] wherein the boost portion comprises a check portion arranged to determine an impedance at the further external connector and:

[0011] when the check portion determines that the impedance at the external connector is below a threshold impedance, to cause the boost portion to output a signal indicating that the supply voltage is ready; and

[0012] when the check portion determines that the impedance at the external connector is above the threshold impedance, to cause the boost portion to boost the supply voltage above the battery voltage and subsequently output a signal indicating that the supply voltage is ready.

[0013] From a second aspect, the invention provides a method of operating an integrated circuit connected to a battery having a battery voltage, wherein the integrated circuit includes a power supply portion and comprising a boost portion and a further external connector;

[0014] the method comprising:

[0015] determining an impedance at the external connector;

[0016] when the impedance at the external connector is determined to be below a threshold impedance, the boost portion outputting a signal indicating that a supply voltage is ready; or

[0017] when the impedance at the external connector is determined to be above the threshold impedance, the boost portion boosting the supply voltage above the battery voltage and subsequently outputting a signal indicating that the supply voltage is ready; and

[0018] the power supply portion providing the supply voltage to other parts of the integrated circuit.

[0019] Thus it will be seen that, in accordance with the invention, by checking whether the impedance of the external connector is above or below a threshold, the power supply portion is able to determine how the external connector has been connected by a user, and thus whether the supply voltage needs to be boosted above the battery voltage. This allows for the same integrated circuit to be used in different modes that require different battery voltages, without the need for an accurate voltage reference.The power supply portion provides the supply voltage, which is based on the battery voltage supplied by the battery, to power the rest of the IC. However, the supply voltage may need to be boosted above the battery voltage when the integrated circuit is used in a configuration requiring a lower-voltage battery. Since such a configuration requires the battery voltage to be boosted (e.g. during start-up and / or normal operation of the IC), which typically requires a capacitor to be connected to the further external connector which can be used along with the boost portion to boost the supply voltage from the battery voltage.

[0020] However, when the IC is used in a higher voltage configuration, the capacitor is not needed and so the further external connector can instead be connected to one of the supply rails, e.g. ground. Thus then the power supply portion determines that the impedance at the external connector is below a threshold impedance, e.g. the external connector is grounded, this indicates that the IC is being used in higher-voltage mode such that a boost capacitor is not required Accordingly, the boost portion will not boost the supply voltage above the battery voltage, and instead it will only output a signal indicating the supply voltage is ready, thereby allowing the power supply portion to operate to start-up the rest of the integrated circuit.

[0021] It can thus be seen that in accordance with the invention, the impedance at the external connector can be used as a simple indicator of the configuration in which the IC is being used. The Applicant has appreciated that this is much simpler to detect than measuring battery voltage during the initial start-up phase when resources are not available.

[0022] To give an example, when the integrated circuit is used in higher voltage mode, e.g. with a battery voltage between 1.7 and 1.98 V, e.g. 1.8 V, the battery voltage may be sufficient to power-up the IC without a boost. There would therefore not be any need for a capacitor to be connected to the further external connector in order to boost the battery voltage. The further external connector may instead be connected to one of the supply rails such as ground, thereby giving a low impedance.

[0023] When viewed from a third aspect the invention comprises an integrated circuit including a power supply portion the power supply portion comprising a batteryconnector for connection to a battery having a battery voltage, a boost portion and a further external connector electrically connected to one side of said battery connector;

[0024] wherein the power supply portion is arranged to output a supply voltage to other parts of in integrated circuit;

[0025] wherein the boost portion comprises a check portion arranged to determine an impedance at the external connector and:

[0026] when the check portion determines that the impedance at the external connector is below a threshold impedance, to cause the boost portion to output a signal indicating that the supply voltage is ready.

[0027] On the other hand, when the check portion determines that the impedance at the external connector is above the threshold impedance, this is taken to indicate that the IC is being used in low voltage made and therefore that a capacitor is connected to the further external connector as a boost is required. Thus, the boost portion will operate to boost the supply voltage above the battery voltage, and then indicate that the supply voltage is ready. When the supply voltage is ready, the rest of the start-up procedure can proceed.

[0028] For example, when used in low voltage mode, a battery voltage between 1.2 and 1.7 V, e.g. 1.5 V might be used. The battery voltage may not be sufficient to power-up the IC. The capacitor is therefore connected to the further external connector so that it can be used in conjunction with the boost portion to boost the battery voltage during startup and / or normal operation of the IC. This will give a high impedance at the further external connector, which is above the threshold impedance.

[0029] When viewed from a fourth aspect the invention comprises an integrated circuit portion including a power supply portion the power supply portion comprising battery connector for connection to a battery having a battery voltage, a boost portion and a further external connector;

[0030] wherein the power supply portion is arranged to output a supply voltage to other parts of in integrated circuit;

[0031] wherein the boost portion comprises a check portion arranged to determine an impedance at the external connector and when the check portion determines that the impedance at the external connector is above the threshold impedance, to cause theboost portion to boost the supply voltage above the battery voltage and subsequently output a signal indicating that the supply voltage is ready.

[0032] In a set of embodiments, the boost portion comprises a boost regulator arranged to boost the supply voltage above the battery voltage. For example, the boost regulator may comprise a boost converter that may alternately switch the battery between being connected in parallel with and in series with a boost capacitor connected to the further external connector (when provided). In a preferred example, the boost regulator comprises a DC-DC charge pump that alternately switches the boost capacitor between the supply voltage and the battery. By alternating the battery connections, the voltage at the output of the boost converter can be up to double the battery voltage. The output of the boost converter is connected to the supply voltage, such that it can be supplied to other parts of the integrated circuit to facilitate their start-up.

[0033] In a set of embodiments the check portion comprises a common-gate amplifier arranged to determine the impedance at the further external connector. The commongate amplifier may comprise an array of resistors and transistors, wherein the common-gate amplifier is arranged to compare the impedance at the further external connector to the array of resistors using the array of transistors, in order to determine whether the impedance at the external connector is above the threshold impedance. The common-gate amplifier then outputs a signal to the boost portion indicating whether a boost is required or not, based on the determined impedance.

[0034] The threshold impedance may be 1 Q. Preferably, the threshold impedance is 1 kQ. This may be sufficiently high enough such that the check portion can easily differentiate between the external connector being connected to ground, or floating (e.g. connected to a capacitor).

[0035] In a set of embodiments the check portion is operated by an asynchronous state machine.

[0036] When the boost operation boosts the supply voltage, it should output that the supply voltage is ready when the supply voltage is sufficiently high. Thus, in a set of embodiments the boost portion comprises a voltage comparator arranged to measure the difference between the battery voltage and the supply voltage, wherein thecomparator portion is arranged to output a signal to indicate that the supply voltage is ready when the supply voltage is at least 1.5 times the battery voltage, e.g. 1.7 times the battery voltage.

[0037] Preferably, the integrated circuit portion comprises a hibernator portion comprising a power-on-reset, wherein the hibernator portion is arranged to indicate to the boost portion to determine the impedance at the further external connector. The hibernator portion may be an always-on module, which can control the boot of the IC. The power-on-reset (POR) may start the integrated circuit portion in a known state when it is first powered up, to enable the integrated circuit portion to safely start-up before the boost operation occurs. Thus, the hibernator may start-up the integrated circuit portion, and then only begin the boost operation when the integrated circuit portion is ready, to prevent a malfunction.

[0038] In a set of embodiments the boost portion provides the signal indicating the supply voltage is ready to the hibernator portion. This enables the hibernator portion to begin powering up the rest of the IC.

[0039] In a set of embodiments the power supply portion is arranged subsequently to adjust the supply voltage to an operating supply voltage after the start-up phase for the rest of the IC has been completed. In other words, the supply voltage may be used to power-up the IC. However, after the IC has been started-up, a lower supply voltage may be used for the normal operation of the IC. Thus, the power module may adjust the supply voltage to a lower operating supply voltage

[0040] Features of any aspect or embodiment described herein may, wherever appropriate, be applied to any other aspect or embodiment described herein. Where reference is made to different embodiments or sets of embodiments, it should be understood that these are not necessarily distinct but may overlap.

[0041] BRIEDF DESCRIPTION OF THE DRAWINGS

[0042] Certain preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0043] Figure 1 is a schematic diagram of an integrated circuit in accordance with the invention in a first configuration;Figure 2 is a schematic diagram of the integrated circuit shown in Figure 1 in a second configuration;

[0044] Figure 3 is a schematic diagram of the boost module shown in Figures 1 and 2; Figure 4 is a schematic diagram of the connection check module shown in Figure 3;

[0045] Figure 5 is a graph of the supply rail waveforms of the integrated circuit shown in Figure 1 during boot;

[0046] Figure 6 is a flow diagram of the operation of the asynchronous state machine operating the connection check module shown in Figure 4.

[0047] DETAILED DESCRIPTION

[0048] Figures 1 and 2 show two different configurations of an integrated circuit (IC) connected to a power supply portion 100, in accordance with the invention, the power supply portion 100 includes a hibernator 102, a boost module 104, reset module 106, a bias module 108, a power module 110, and a digital controller 112. The IC is powered by an off-chip battery (not shown) connected to a battery pin 124 and to ground. Various off-chip capacitors 114, 115, 117, 119 are also provided depending on the configuration.

[0049] The boost module 104 is connected to the hibernator 102 and to the reset, bias, and power modules 106, 108, 110. The hibernator 102 is also connected to the reset, bias, and power modules 106, 108, 110. It also provides a positive supply rail VDD 122 to the rest of the IC. The digital controller 112 is also connected to the reset, bias, and power modules 106, 108, 110. The hibernator 102, boost module 104 and the reset, bias and power modules 106, 108, 110 are hard coded in a sequence to start-up the IC when the IC is first turned on. After start-up, the control of the power module 110 is passed to the digital controller 112.

[0050] The boost module 104 and the hibernator 102 are connected to the battery pin 124. In the case of the boost module 104 this is by means of an off-chip link to a connection point 126 to the boost module 104. This may alternatively be an on-chip link in other implementations of the invention. The battery pin 124 is connected to a battery capacitor 117, which charges to the same voltage as the battery.The boost module 104 includes an external connector 118 and a ground connection 120. As described below with reference to Figures 3 and 4, the boost module 104 detects how the external connector 118 has been connected. If a low-voltage battery is used, i.e. the IC is to be used in low voltage mode, the boost module 104 will be required to boost the supply voltage from the battery voltage (e.g. for start-up), and thus the external connector 118 must be connected to an off-chip boost capacitor 114, as shown in the configuration of Figure 1. The output from the boost module 104, i.e. the boosted supply voltage is stored across a supply capacitor 119.

[0051] However, if the IC is to be used in a high-voltage mode with a suitably higher voltage battery, a boost is not required, and the external connector 118 is grounded as shown in the configuration of Figure 2.

[0052] Therefore, as will be described in greater detail below, the boost portion 104 determines how the external connector 118 has been connected and uses this to determine whether the boost module 104 will output a boosted supply voltage greater than the battery voltage, or simply provide the battery voltage to the positive supply rail 122.

[0053] The hibernator 102 includes a power-on-reset (POR) module (not shown) and an asynchronous state machine (not shown) at the battery input to the hibernator 102. The POR uses a resistor and a capacitor (not shown) with the values selected such that the capacitor takes a predictable and constant time to charge up when the battery is first connected.

[0054] Figure 3 is a more detailed diagram of the boost module 104 shown in Figures 1 and 2. The connection 101 to the hibernator 102 allows receipt of a boost enable signal 101, which triggers operation of a comparison module 133. The comparison module 133 includes a first voltage comparator 132 and a second voltage comparator 134, which operate in parallel.

[0055] The first voltage comparator 132 compares the voltage across the supply capacitor 119 to the voltage across the battery capacitor 117, and has a threshold of 100 mV. Thus, when the voltage across the supply capacitor 119 is within approximately 100mV of the battery capacitor 117, the first voltage comparator 132 will output a check signal 131.

[0056] The second voltage comparator 134 compares the voltage across a voltage divider which is in parallel with the supply capacitor 119 to the voltage across the battery capacitor 117, such that it has a threshold of 1.7 times the battery voltage. Therefore, when the supply voltage is boosted to approximately 1.7 times the battery voltage, the second voltage comparator 134 will output a signal.

[0057] The boost module 104 also includes a first level shifter 146 and a second level shifter 148. The first and second level shifters 146, 148 are logic level translators, and are used to translate signals between the boost module 104 and the digital controller 112, as these operate on different supply domains. The first and second level shifters 146, 148 can be operated by the digital controller 112 to disable the boost operation, depending on the impedance at the external connector 118.

[0058] The outputs of the first voltage comparator 132 and the first level shifter 146 are fed to an AND gate 144. When the AND gate 144 receives a signal from both the first voltage comparator 132 and the first level shifter 146, it outputs a check required signal 145 to a connection check module 130. The first level shifter 146 is arranged to output logic high by default, i.e. during start-up operation of the boost module 104.

[0059] The connection check module 130 detects whether the external connector 118 is connected to a boost capacitor 114 as in the configuration shown in Figure 1 , or if it is grounded as in configuration shown in Figure 2, by determining the impedance at the external connector 118, as described with reference to Figure 4. The connection check module is operated by an asynchronous state machine and timer 138, as described with further below reference to Figure 6.

[0060] Figure 4 is a schematic diagram of the connection check module 130 shown in Figure 3. The connection check module 130 includes an asynchronous state machine 139 connected to a timer 138, and a common-gate amplifier 400 connected to the asynchronous state machine 139. The timer 138 initiates the asynchronous state machine 139 to start the impedance measurement by sending the check requiredsignal 145 to the common-gate amplifier 400, when the output from the AND switch 144 goes high.

[0061] The common-gate amplifier 400 includes a skewed current mirror, made up of a first and second NMOS transistor 158, 161 each with a first and second resistor 159, 153 connected between their drains and the positive supply rail 120. The first and second resistors 159, 153 each have a resistance of 200 Q.

[0062] The drain of the first transistor 158 is connected to the external connector 118 at the drain of a first capacitor 158 via a first resistor 159. The gate of a third NMOS transistor 160 is connected to the source of the first capacitor 158, with its drain connected to the positive supply rail 120 and the source connected to an inverter 150.

[0063] The source of the fourth PMOS transistor 151 is connected to fourth resistor 152 and the gate and drain of the second transistor 161. The drain is connected to the supply voltage 124. The fourth resistor 152 has a resistance of 10 kQ.

[0064] The source of the fifth PMOS transistor 154 is connected to fifth resistor 155, the source of the first NMOS transistor 158, and the gate of the third NMOS transistor 160. The drain is connected to the supply voltage 124. The fifth resistor 155 has a resistance of 10 kQ. The source of the sixth PMOS transistor 156 is connected to sixth resistor 157 and the inverter 150. The sixth resistor 157 has a resistance of 100 kQ.

[0065] The common-gate amplifier is dimensioned to output a high signal when the output impedance at the external connector 118 is more than 1 kQ. The inverter 150 will thus output a low signal to the asynchronous state machine 139 when the impedance at the external connector 118 is above the 1 kQ threshold, and based on the result, the asynchronous state machine 139 will either output a boost required signal 149, or it will output an override signal 147.

[0066] Returning to Fig. 3 it can be seen that the override signal 147 is provided to an OR gate 136, the other input to which is derived from the second voltage comparator 134. The output 103 from the OR gate provides the Boost Ready signal 103 from the boost module 104 back to the hibernator 102. The override signal 147 is also provided to the second level shifter 148. The second level shifter 148 outputs a disabling signal163 to the digital controller 112, to indicate that the integrated circuit 100 is being used in a high-voltage mode. The digital controller 112 then outputs a disable signal 109 to the first level shifter, which in turn shifts the first level shifter 146 to output logic low, thus disabling the boost operation by turning off the check required signal 145.

[0067] The boost module further includes a second digital controller 140 and a power-stage switching section 142. This includes a series of four transistors 143a-d connected in series and, at various junctions thereof, to the external battery and capacitor connections, 116, 118, 126. It also includes a bypass transistor 139.

[0068] In the configuration shown in Figure 1, the external connector 118 is connected at one end to the off-chip boost capacitor 114. The other end of the boost capacitor 114 is connected to another input 116 to the boost module 104. This arrangement is used when the IC is being used in low voltage mode, e.g. a 1.5 V battery is connected. Since the battery supplies a lower voltage than is needed to start-up and / or operate the IC, the boost capability of the IC, which uses the boost capacitor, is required. .

[0069] Operation in the configuration shown in Figure 1, will now be described with further reference to Figure 5.

[0070] Figure 5 is a graph of various signals in the power supply portion of the integrated circuit 100 at various times during the initial start-up phase when the IC is in the configuration shown in Figure 1. The battery is first connected at a first time to. This causes the voltage across the battery capacitor 117 to start to rise. The second digital controller 140 defaults to providing a ‘short’ signal 141 which causes the bypass transistor 139 to conduct, the supply capacitor 119 is thus effectively shorted to the battery voltage, such that voltage across the supply capacitor 119 and the voltage across the battery capacitor 117 charge to approximately the battery voltage.

[0071] The POR of the hibernator 102 is set to elapse at a second time h (which gives enough time for the battery capacitor 117 and supply capacitor 119 to charge), and output the boost enable signal 101 to enable the boost module 104.

[0072] At a third time t2, the first voltage comparator 132 detects that the voltage across the supply capacitor 119 and the voltage across the battery capacitor 117 are within100mV of each other, and its output goes high which sends the output of the AND gate high since the output of the first level shifter 146 defaults high. This enables the connection check module 130 to check the impedance at the external connector 118. The connection check module 130 determines that the external connector 118 is connected to the boost capacitor 114 since it detects an impedance above the 1 kQ threshold and so outputs the boost required signal 149 to the second digital controller 140.

[0073] Upon receiving the boost required signal 149, the second digital controller 140 triggers the short signal 141 to go low, switching off the bypass transistor 139 such that the supply capacitor 119 and the positive supply rail VDD 122 are no longer shorted to the battery pin 124 and the battery capacitor 117. This allows the power-stage 142 at a fourth time t3to operate as a boost converter, to boost the supply voltage across the supply capacitor 119 and the positive supply rail VDD 122. The transistors 143a-d of the power-stage 142 the battery pin 124 from being connected in parallel with and in series with the boost capacitor 114, to charge the supply voltage across the supply capacitor 119 above the battery voltage. Thus, the voltage at the positive supply rail VDD 122 is boosted above the battery voltage.

[0074] At a fifth time t4, the second voltage comparator 124 detects that the voltage across the supply capacitor 119 is 1.7 times the voltage across the battery capacitor 117, causing its output to go high. This puts the output of the OR gate 136 high and so the boost module outputs the ready signal 103 to the hibernator 102.

[0075] The hibernator 102 then enables power-up of the rest of the IC, by sending the startup signal 105 to the reset, bias and power modules 106, 108, 110 and the digital controller 112. The start-up signal 105 also enables the power module 110 to enable the 0.9V operating capacitor 115 to charge up, to enable the 0.9V domain. The 0.9V domain is the operating domain of the digital controller 112, and thus the digital controller 112 is enabled when the 0.9V domain is enabled.

[0076] The reset module 106 finally sends a reset signal 107 to the boost module 104 at a sixth time ts, to de-assert the ready signal 103, and pass control of the power module 110 and bias module 108 from the hibernator 102 to the digital controller 112 in the 0.9V domain, i.e. from the hibernator 102 driven power-up / boot state to the normaloperation of the integrated circuit 100 as controlled by the digital controller 112. The boost module 104 may remain on, as the first level shifter 146 is still in its default logic high state, but the boost enable signal 101 from the hibernator is turned off. .

[0077] In the configuration shown in Figure 2, the external connector 118 is connected to ground 120. This arrangement is used when the IC is operated in high voltage mode -i.e. a 1.8V battery is connected. In this configuration the battery supplies enough voltage to start-up the IC without boosting. The battery pin 124 and the battery capacitor 117 are connected to the positive supply rail 122 (i.e. to the supply voltage), and there is no boost capacitor or supply capacitor present. Thus, the supply voltage is equal to the battery voltage for start-up of the integrated circuit 100.

[0078] In the configuration shown in Figure 2, connection check module 130 detects the impedance of the external connector 118 is low (i.e. below the threshold impedance) and outputs an override signal 147 straight to the OR gate 136 indicating that the supply voltage is ready. Upon receiving this signal, the OR gate 136 will output the ready signal 103 to the hibernator 102, such that the hibernator 102 can enable power up by sending a start-up signal 105 to the reset, bias and power modules 106, 108, 110, and the power module 110 can enable the 0.9V domain to enable the digital controller 112. The override signal 147 is also provided to the second level shifter 148, which disables the boost operation completely by turning off the checked required signal 145 via the digital controller 112 and the first level shifter 146 as described above.

[0079] Thus, in the configuration shown in Figure 2, the second digital controller 140 is not enabled and the boost operation does not occur; the supply voltage at the positive supply rail VDD 122 is simply the battery voltage.

[0080] Figure 6 is a flow diagram of the asynchronous state machine 139 operating the connection check module 130 shown in Figure 4. At a first step 162 the connection check module is reset and the timer (REQ_TIMER) and check required (REQ_SWK) are zero. At a second step 164 the timer is initialised and set to 1, indicating that the timer is ready.At a third step 166 the connection check module 130 receives the check required signal 145 and thus the check required is set to 1. This triggers the connection check module 130 to check the state of the external connector 118.

[0081] At a fourth step 168 the timer is cleared and set back to zero. Then, if the connection check module 130 has determined that a boost is not required, at a fifth step 170 the check required is set to zero, and the connection check module 130 outputs the override signal 147 indicating the voltage is ready.

[0082] If the connection check module 130 determines that a boost is required, at a sixth step 172 the check required is set to zero, and the connection check module 130 outputs the boost required signal 149 indicating a boost is required.

[0083] It will be appreciated by those skilled in the art that the invention has been illustrated by describing one or more specific embodiments thereof, but is not limited to these embodiments; many variations and modifications are possible, within the scope of the accompanying claims.

Claims

CLAIMS1. An integrated circuit including a power supply portion the power supply portion comprising battery connector for connection to a battery having a battery voltage, a boost portion and a further external connector;wherein the power supply portion is arranged to output a supply voltage to other parts of the integrated circuit;wherein the boost portion comprises a check portion arranged to determine an impedance at the further external connector and:when the check portion determines that the impedance at the external connector is below a threshold impedance, to cause the boost portion to output a signal indicating that the supply voltage is ready; andwhen the check portion determines that the impedance at the external connector is above the threshold impedance, to cause the boost portion to boost the supply voltage above the battery voltage and subsequently output a signal indicating that the supply voltage is ready.

2. The integrated circuit as claimed in claim 1 , wherein when the impedance at the further external connector is above the threshold impedance, the further external connector is connected to a boost capacitor;wherein the boost portion is arranged to alternately switch the battery between being connected in parallel with and in series with a boost capacitor connected to the further external connector to boost the supply voltage above the battery voltage.

3. The integrated circuit as claimed in claim 1 or 2, wherein the boost portion comprises a boost converter arranged to boost the supply voltage above the battery voltage.

4. The integrated circuit as claimed in any preceding claim, wherein the threshold impedance is 1 kQ.

5. The integrated circuit as claimed in any preceding claim, wherein the check portion comprises a common-gate amplifier arranged to determine the impedance at the further external connector.

6. The integrated circuit as claimed in any preceding claim, wherein the check portion is operated by an asynchronous state machine.

7. The integrated circuit as claimed in any preceding claim, wherein the boost portion comprises a voltage comparator arranged to measure the difference between the battery voltage and the supply voltage, wherein the comparator portion is arranged to output a signal to indicate that the supply voltage is ready when the supply voltage is at least 1.7 times the battery voltage.

8. The integrated circuit as claimed in any preceding claim, comprising a hibernator portion comprising a power-on-reset, wherein the hibernator portion is arranged to indicate to the boost portion to determine the impedance at the further external connector.

9. The integrated circuit as claimed in claim 8, wherein the boost portion provides the signal indicating the supply voltage is ready to the hibernator portion.

10. The integrated circuit as claimed in any preceding claim, wherein the supply portion is arranged subsequently to adjust the supply voltage to an operating supply voltage after the start-up phase for the rest of the integrated circuit has been completed.

11. An integrated circuit including a power supply portion the power supply portion comprising a battery connector for connection to a battery having a battery voltage, a boost portion and a further external connector electrically connected to one side of said battery connector;wherein the power supply portion is arranged to output a supply voltage to other parts of in integrated circuit;wherein the boost portion comprises a check portion arranged to determine an impedance at the external connector and:when the check portion determines that the impedance at the external connector is below a threshold impedance, to cause the boost portion to output a signal indicating that the supply voltage is ready.- 17 - 12. An integrated circuit portion including a power supply portion the power supply portion comprising battery connector for connection to a battery having a battery voltage, a boost portion and a further external connector;wherein the power supply portion is arranged to output a supply voltage to other parts of in integrated circuit;wherein the boost portion comprises a check portion arranged to determine an impedance at the external connector and when the check portion determines that the impedance at the external connector is above the threshold impedance, to cause the boost portion to boost the supply voltage above the battery voltage and subsequently output a signal indicating that the supply voltage is ready.

13. A method of operating an integrated circuit connected to a battery having a battery voltage, wherein the integrated circuit includes a power supply portion and comprising a boost portion and a further external connector;the method comprising:determining an impedance at the external connector;when the impedance at the external connector is determined to be below a threshold impedance, the boost portion outputting a signal indicating that a supply voltage is ready; orwhen the impedance at the external connector is determined to be above the threshold impedance, the boost portion boosting the supply voltage above the battery voltage and subsequently outputting a signal indicating that the supply voltage is ready; andthe power supply portion providing the supply voltage to other parts of the integrated circuit.

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