Switching circuit with smooth start, and switching control circuit and method

Abstract

The invention relates to a switch circuit with a smooth starting function and a switch control circuit and method. The switch control circuit is used for controlling a path switch and a current sensing resistor which are connected in series between an input voltage and an output voltage. The switch control circuit includes: an amplifier that controls a gate voltage of the path switch based on a voltage drop across the current sense resistor to perform a current-limited gentle start; the slope detection circuit is coupled to the output voltage and is used for monitoring the rising slope of the output voltage; and a pull-down switch coupled between the gate of the path switch and a prohibition potential. When the slope detection circuit detects that the rising slope of the output voltage is lower than a preset slope threshold value, the pull-down switch is triggered to be turned on, and therefore the path switch is turned off.

Description

Technical Field

[0001] This invention relates to a switching circuit, particularly a switching circuit for hot-plug applications. The invention also relates to its switching control circuit and control method. This invention enables efficient and smooth start-up operation and reduces the safe operating area (SOA) requirement of the path switches in the switching circuit. Background Technology

[0002] In hot-plug applications, implementing a smooth start-up mechanism is crucial for reducing interference with the backplane power supply and lowering the safe operating area (SOA) requirements of series power switches (typically N-type MOSFETs). By gradually charging the large output capacitor with a controlled, moderate current, heat dissipation can be effectively achieved using the MOSFET's heatsink metal components and board traces, thereby reducing the stress on the MOSFET.

[0003] Figure 1 and Figure 2 Two main prior art methods for smooth startup are shown: a gate voltage slope control method and a current limiting method.

[0004] Figure 1 A multi-phase switching circuit is illustrated using a gate voltage slope-controlled smooth startup method. The multi-phase switching circuit 100 includes multiple switching circuits (e.g., switching circuits 51 and 52) coupled between the input voltage VIN and the output voltage VOUT. Each switching circuit includes a path switch SP located between VIN and VOUT to control current flow. In this embodiment, smooth startup is achieved by controlling the rising slope of the gate voltage VG of the path switch. Since SP is an NMOSFET, a charge pump 28 is configured to provide the required gate voltage, while a current source 38 supplies a constant charging current ICH. This configuration ensures that VG has a stable rising slope, thereby achieving the smooth startup function.

[0005] In the gate voltage slope control method, the MOSFET gate is gradually charged by a constant current source, causing the source terminal (connected to the output capacitor Co) to rise with the gate potential and a threshold voltage offset. The smooth startup current ISS flowing through the MOSFET and the current flowing into Co are given by the following formulas:

[0006] ISS = (dVOUT / dt) × Co

[0007] The smooth start-up current (ISS) is typically set below the current limit threshold to quickly terminate the smooth start-up operation upon detection of an output short circuit. By immediately terminating the smooth start-up when the current reaches the threshold, MOSFET stress is minimized, thereby reducing SOA requirements. However, threshold voltage variations among different MOSFETs can cause inconsistencies in current distribution when multiple devices are connected in parallel. Therefore, in this configuration, gate voltage slope control methods are limited in terms of current sharing accuracy.

[0008] Figure 2 A schematic diagram of another prior art switching circuit is shown, illustrating a current-limited smooth start-up method. The multi-phase switching circuit 200 includes multiple switching circuits (e.g., switching circuits 53 and 54). Each switching circuit, such as switching circuit 53, includes a path switch SP connected in series between VIN and VOUT and a current-sensing resistor RSNS. Each switching circuit also includes an amplifier 48 with an offset voltage VOS coupled across RSNS to sense the current in the path switch SP. The amplifier's output controls the gate voltage VG of the path switch SP, achieving a constant current during smooth start-up through feedback control to control the current flowing through RSNS.

[0009] In the current-limiting method, the gate voltage VG is adjusted to maintain a constant current, typically set to a low level (e.g., 10% of the maximum load current) to reduce SOA requirements. By setting a longer, smoother start-up time, the output capacitor can be fully charged, and margins are included for variations in current-limiting accuracy and capacitance tolerance. Compared to the gate voltage slope control method, this method offers higher current distribution accuracy in multi-device parallel applications and is unaffected by MOSFET threshold voltage variations.

[0010] However, the longer smooth startup time presents challenges in fault conditions such as output short circuits. Because the current limiter is active in both normal and fault conditions, the system cannot distinguish between these states and therefore cannot shorten the smooth startup time. This can lead to sustained power loss and temperature rise at the path switch SP, increasing the risk of failure under sustained fault conditions.

[0011] In view of the above, and to overcome the shortcomings of the prior art, the present invention proposes a method and circuit designed to solve these problems. The switching circuit of the present invention can achieve high-precision current balance during smooth startup, while also possessing the ability to quickly turn off path switches to prevent damage during output load failures and reduce SOA requirements. Summary of the Invention

[0012] From one perspective, the present invention provides a switch control circuit for controlling a path switch and a current sensing resistor connected in series between an input voltage and an output voltage. The switch control circuit includes: an amplifier that controls the gate voltage of the path switch based on the voltage drop across the current sensing resistor to perform a smooth start-up with current limiting; a slope detection circuit coupled to the output voltage for monitoring the rising slope of the output voltage; and a pull-down switch connected between the gate of the path switch and a disable potential. When the slope detection circuit detects that the rising slope of the output voltage is lower than a preset slope threshold, it triggers the pull-down switch to turn on, thereby turning off the path switch.

[0013] In a preferred embodiment, the switch control circuit further includes a charge pump that, after a smooth start-up, raises the gate voltage of the path switch to a high potential generated by the charge pump, thereby fully turning on the path switch.

[0014] In a preferred embodiment, the slope detection circuit includes an analog-to-digital converter (ADC) coupled to the output voltage to convert the output voltage into a digital signal; and a logic circuit that calculates the rising slope of the output voltage based on the digital signal and compares the rising slope with a preset slope threshold to generate a control signal for controlling the pull-down switch.

[0015] In a preferred embodiment, the switch control circuit allows the rise slope of the output voltage to be lower than a preset slope threshold within a preset time window, thereby achieving the debouncing function.

[0016] In a preferred embodiment, when the rise rate of the output voltage is detected to be lower than a preset slope threshold and the path switch is turned off, the switch control circuit attempts to restart smoothly after a preset time delay.

[0017] In a preferred embodiment, the switch control circuit counts and records the number of retries for a smooth start, and when the number of retries reaches a preset upper limit, the path switch remains off.

[0018] From another perspective, the present invention provides a switching circuit comprising: a path switch and a current sensing resistor connected in series between an input voltage and an output voltage; and a switching control circuit comprising: an amplifier that controls the gate voltage of the path switch based on the voltage drop across the current sensing resistor to perform a current-limited smooth start; a slope detection circuit coupled to the output voltage for monitoring the rising slope of the output voltage; and a pull-down switch connected between the gate of the path switch and a disable potential; wherein, when the slope detection circuit detects that the rising slope of the output voltage is lower than a preset slope threshold, it triggers the pull-down switch to turn on, thereby turning off the path switch.

[0019] From another perspective, the present invention provides a method for controlling a path switch connected in series between an input voltage and an output voltage. The method includes: controlling the gate voltage of the path switch to perform a smooth start-up of current limiting of the output voltage; monitoring the rise rate of the output voltage; comparing the monitored rise rate with a preset rise rate threshold; and turning off the path switch when the rise rate is lower than the preset rise rate threshold.

[0020] In a preferred embodiment, the method further includes: during the smooth start-up process, allowing the rising slope to be lower than a slope threshold within a preset time window to achieve the de-jitter function.

[0021] In a preferred embodiment, after the path switch is turned off due to the rising slope being lower than a preset slope threshold, the method further includes: retrying a smooth start after a preset time delay.

[0022] In a preferred embodiment, the method further includes: counting and recording the number of retries during a smooth start; and keeping the path switch off when the number of retries reaches a preset upper limit.

[0023] The following detailed description through specific embodiments will make it easier to understand the purpose, technical content, features and effects achieved by the present invention. Attached Figure Description

[0024] Figure 1 A schematic diagram of a prior art switching circuit is shown.

[0025] Figure 2 A schematic diagram of a switching circuit of another prior art is shown.

[0026] Figure 3 A schematic diagram of a switching circuit according to an embodiment of the present invention is shown.

[0027] Figure 4 Displayed corresponding to Figure 3 A more detailed embodiment of the switching circuit of the present invention.

[0028] Figure 5 The diagram shows the operation waveforms of an embodiment of the present invention, illustrating the normal state and the failure of a smooth start-up.

[0029] Figure 6 The diagram shows an operation waveform of another embodiment of the present invention, demonstrating a smooth start-up with de-jitter function.

[0030] Figure 7 The diagram shows the operation waveforms of an embodiment of the present invention with a retry function.

[0031] Figure 8 The operation flowchart of the present invention is shown.

[0032] Explanation of symbols in the diagram

[0033] 100, 200, 300: Switching circuits

[0034] 28, 63: Charge pump

[0035] 38: Current source

[0036] 48: Amplifier

[0037] 51~54: Switching Circuit

[0038] 60: Switch control circuit

[0039] 61: Slope Detection Circuit

[0040] 62: Amplifier

[0041] 63: Charge Pump

[0042] 611: Analog-to-Digital Converter (ADC)

[0043] 612: Logic Circuits

[0044] ADC: Analog-to-Digital Converter

[0045] COUT / Co: Output capacitor

[0046] CV1~CV8: Waveforms

[0047] ICH: Charging Current

[0048] ISS: Smooth starting current

[0049] Lth: Preset slope threshold

[0050] LV1, LV2, LV3: Slope

[0051] MOSFET: Metal-Oxide-Semiconductor Field-Effect Transistor

[0052] n: Number of retries

[0053] RSNS: Current sensing resistor

[0054] SOA: Safe Operating Area

[0055] SP: Path Switch

[0056] SPD: Pull-down switch

[0057] t1, t2, t2', t3, t4, t5, t6: Time points

[0058] Td: Scheduled delay time

[0059] Tw: Preset time window

[0060] VG: Gate voltage

[0061] VIN: Input voltage

[0062] VOS: Offset Voltage

[0063] VOUT: Output voltage

[0064] VPD: Pull-down control signal Detailed Implementation

[0065] The accompanying drawings in this invention are schematic and are primarily intended to illustrate the coupling relationships between circuits and the relationships between signal waveforms. The circuits, signal waveforms, and frequencies are not drawn to scale. For clarity, many practical details will be described in the following description, but this is not intended to limit the scope of the patent application.

[0066] Figure 3 A schematic diagram of a switching circuit according to an embodiment of the present invention is shown. The switching circuit 300 includes a path switch SP connected in series between the input voltage VIN and the output voltage VOUT, a current sensing resistor RSNS, and a switching control circuit 60. The switching control circuit 60 includes an amplifier 62, a charge pump 63, a pull-down switch SPD, and a slope detection circuit 61. The amplifier 62 has an offset voltage VOS and is used to adjust the gate voltage VG of the path switch SP based on the voltage drop across the current sensing resistor RSNS and the offset voltage VOS, thereby achieving a smooth start-up of the output voltage VOUT in a current-limited manner.

[0067] The output of charge pump 63 is connected to the gate voltage VG to boost the gate voltage VG to a higher level during the final stage of smooth startup, thus fully turning on the path switch SP. Slope detection circuit 61 senses the rising slope dVOUT / dt of the output voltage VOUT and generates a pull-down control signal VPD. The pull-down switch SPD is positioned between the gate voltage VG and ground potential. When the pull-down control signal VPD indicates that pull-down control is activated, the pull-down switch SPD pulls the gate voltage VG to an inhibit level (e.g., ground potential), thereby turning off the path switch SP.

[0068] In one embodiment, when the slope detection circuit 61 senses that the rising slope dVOUT / dt of the output voltage VOUT is lower than a preset slope threshold Lth, it enables the pull-down control signal VPD, turns on the pull-down switch SPD, pulls down the gate voltage VG, and thus turns off the path switch SP. Under current-limited conditions, if the current supplied to the output capacitor COUT and the load is insufficient to make the output voltage VOUT rise according to the preset slope, the slope detection circuit 61 can determine that a fault may have occurred, such as a short circuit in the load RL, and then trigger the pull-down switch SPD to turn off the path switch SP. It is worth noting that although this embodiment only shows one switching circuit, the present invention can also be used in applications where multiple switching circuits are connected in parallel, and can achieve precise current balance among multiple path switches during smooth startup.

[0069] Figure 4 Displayed corresponding to Figure 3 A more detailed embodiment of the switching circuit of the present invention is provided. In this embodiment, the slope detection circuit 61 includes an analog-to-digital converter (ADC) 611 and a logic circuit 612. The ADC 611 is coupled to the output voltage VOUT and converts VOUT into a corresponding digital signal reflecting the potential of the output voltage. The logic circuit 612 calculates the rising slope dVOUT / dt of the output voltage VOUT based on the digital signal generated by the ADC 611 and a clock signal CLK, and compares it with a preset slope threshold Lth. When the logic circuit 612 detects that the slope dVOUT / dt of the output voltage VOUT is lower than the preset slope threshold Lth, it generates a pull-down control signal VPD, which in turn controls the pull-down switch SPD to turn off the path switch SP. This design can quickly respond when the rising slope of the output voltage is insufficient, preventing potential faults such as load short circuits.

[0070] Figure 5 The diagram shows the operation waveforms of an embodiment of the present invention, illustrating the normal state and the failure of a smooth start-up. Figure 5 The upper half of the waveform shows the changes in output voltage VOUT under normal (CV1) and fault (CV2) conditions. The lower half of the waveform shows the rising slope of the corresponding output voltage VOUT, which is CV3 under normal conditions and CV4 under fault conditions.

[0071] Under normal conditions, the switch control circuit 60 begins a smooth start-up at time t1, as shown by waveforms CV1 and CV3. During the smooth start-up period from t1 to t3, the output voltage VOUT rises steadily with a slope of LV1, and LV1 is greater than the preset slope threshold Lth. Therefore, the slope detection circuit 61 determines that this is a normal smooth start-up state. Furthermore, after the smooth start-up is completed at time t3, the output voltage has risen to the preset target value, and the switch control circuit 60 raises the gate voltage VG to a higher level, causing the path switch SP to be fully turned on.

[0072] In the event of a fault, the switching control circuit 60 starts smoothly at time t1, as shown in waveforms CV2 and CV4. However, because the rising slope of the output voltage VOUT is too low, its slope value LV2 is lower than the preset slope threshold Lth. Therefore, the switching control circuit 60 pulls the gate voltage VG down to zero at time t2, turning off the path switch SP, so that after time t2, the output voltage VOUT also drops to a low level. It should be noted that the rising slope of the output voltage does not need to be detected outside of time points t1 to t3, and therefore is not plotted.

[0073] Figure 6 The diagram shows an operational waveform of another embodiment of the present invention, illustrating a smooth start-up with debounce functionality. Specifically, Figure 6 The upper half of the waveform shows the output voltage VOUT waveform CV5, and the lower half shows the corresponding output voltage rise slope waveform CV6. Starting from time point t1, the switching control circuit performs a smooth start-up. During the period from time point t1 to t2, the output voltage VOUT rises at a fixed slope LV1. This slope LV1 is higher than the preset slope threshold Lth, indicating that the smooth start-up is proceeding smoothly.

[0074] Starting from time point t2, the rising slope of the output voltage VOUT becomes a gentler LV2, which is lower than the slope threshold Lth. As mentioned above... Figure 5 In some embodiments, a slope below Lth may be identified as a fault, causing a smooth start-up to be interrupted. However, as... Figure 6 As shown, this embodiment introduces a deglitch function, which allows the switch control circuit to allow the slope to be lower than the slope threshold Lth for a short period of time.

[0075] Specifically, due to factors such as load changes, the slope LV2 of the output voltage VOUT may be briefly lower than Lth between time points t2 and t2'. However, due to the debouncing function, the switching control circuit allows the slope to be temporarily lower than Lth within a preset time window Tw. Therefore, a smooth start-up can continue.

[0076] Starting from time point t2', the rising slope of the output voltage VOUT returns to LV3, which is higher than Lth, and continues until time point t3. At this time, the output voltage VOUT reaches its final highest level, and the smooth start-up is successfully completed.

[0077] In this embodiment, by introducing a debouncing function, the switching control circuit becomes insensitive to brief drops in the slope, avoiding misjudgments of faults due to momentary interference. This configuration enhances the system's stability and fault tolerance, ensuring a smooth start-up process.

[0078] Figure 7 The diagram illustrates the operation waveforms of one embodiment of the present invention with a retry function. The upper waveform CV7 shows the change of the output voltage VOUT over time, encompassing the process of multiple restart attempts. The lower waveform CV8 corresponds to the change of the rising slope dVOUT / dt of the output voltage VOUT over time.

[0079] At time t1, the switch control circuit initiates a smooth initial startup, and the output voltage VOUT gradually increases as the gate voltage VG of the path switch SP rises. However, at time t2, the slope detection circuit 61 detects that the rising slope dVOUT / dt of the output voltage VOUT is lower than the preset slope threshold Lth. The switch control circuit determines that a fault may exist, therefore pulls the gate voltage VG down to zero, turns off the path switch SP, and causes VOUT to decrease or remain at a low level.

[0080] In this embodiment, after a predetermined delay time Td, at time point t3, the switch control circuit automatically performs a second smooth start-up attempt, and the output voltage VOUT begins to rise again. Since the slope dVOUT / dt is detected to be lower than the threshold Lth again at time point T4, the switch control circuit repeats the above process.

[0081] The switch control circuit can be set with a maximum number of retries (e.g., three); if the number of retries exceeds the set limit, the switch control circuit will remain off.

[0082] Depend on Figure 7 As can be seen, when the rising slope of VOUT is lower than the threshold Lth, the switch control circuit of this embodiment can attempt to restart multiple times, with a predetermined delay time Td between each attempt. This retry mechanism improves system reliability, allowing temporary faults or erroneous information to attempt automatic recovery without user intervention, thereby enhancing the fault tolerance of the switch circuit.

[0083] Figure 8The operation flowchart of the present invention is shown. Step S0: Smooth start-up begins, wherein the switch control circuit 60 is activated, and the output voltage VOUT begins to rise as the gate voltage VG of the path switch SP begins to rise. Next, proceed to step S1: Monitoring the output slope, wherein the slope detection circuit 61 continuously monitors the rising slope dVOUT / dt of the output voltage VOUT.

[0084] Next, proceed to step S2: slope comparison, where the detected slope dVOUT / dt is compared with a preset slope threshold Lth. If the slope dVOUT / dt is higher than Lth, proceed to step S3. If the slope dVOUT / dt is lower than Lth, proceed to step S4. Step S3: Determine whether VOUT has reached the target value or has reached the preset smooth start time; if not, return to step S1 and continue the smooth start process. If yes, proceed to step S9, where the path switch SP is kept on during the normal power supply procedure to supply power to the load.

[0085] On the other hand, in step S4, the gate voltage VG is pulled down to zero, and the path switch SP is turned off. Next, proceed to step S5: check the number of smooth start retries. If the number of retries has not reached the upper limit, proceed to step S6. Step S6: wait for a predetermined delay time Td, increment the retry counter n, and then return to step S0 to retry the start-up. If the number of retries n has reached the upper limit, proceed to step S7. Step S7: enter protection mode, where the switch control circuit 60 remains off.

[0086] In one embodiment, some steps of the aforementioned process can be omitted, such as steps S5 and S6, that is, the retry function is not included. Once it is confirmed in step S4 that the output voltage slope dVOUT / dt is lower than the slope threshold Lth, the process directly jumps to step S7.

[0087] Furthermore, in one embodiment, the aforementioned step S2 can be replaced by step S2'. Step S2': Compare the detected slope dVOUT / dt with a preset slope threshold Lth, and incorporate a time window Tw. If the slope dVOUT / dt is higher than Lth: Proceed to step S3. If the time for which the slope dVOUT / dt is lower than Lth is longer than the time window Tw, proceed to step S4; otherwise, proceed to step S3.

[0088] Figure 8 The decision-making and operation process of the switch control circuit 60 during the startup process is described in detail in this embodiment. Figure 7 The waveform allows for multiple retries when a fault is detected, improving the fault tolerance of the switching control circuit. Furthermore, the number of retries n and the delay time Td can be adjusted by the user according to application requirements.

[0089] This invention offers several advantages. First, by employing a current-limiting method and actively controlling the MOSFET gate voltage to set the current to a fixed value, it provides better current sharing capability in applications where multiple switching circuits are connected in parallel to charge a large output capacitor for smooth startup. This is unaffected by differences in MOSFET threshold voltages, enabling more accurate current distribution. Second, the switching control circuit continuously monitors the output voltage rise rate (dVOUT / dt), allowing for rapid cessation of smooth startup upon detecting a fault (such as an output short circuit). The response time can be reduced from hundreds of milliseconds to several milliseconds, significantly reducing the stress on the MOSFET and thus lowering the requirement for a safe operating area (SOA), saving system costs. Furthermore, by introducing debouncing functionality and a retry mechanism, the system possesses a certain degree of fault tolerance, allowing for brief slope drops and multiple startup attempts, improving system stability and reliability.

[0090] The present invention has been described above with reference to preferred embodiments. However, the above description is only intended to facilitate understanding of the invention by those skilled in the art and is not intended to limit the scope of the invention. The described embodiments are not limited to individual application and can also be used in combination. For example, two or more embodiments can be used in combination, and some components of one embodiment can be used to replace corresponding components in another embodiment. Furthermore, within the same spirit of the invention, those skilled in the art can conceive of various equivalent changes and combinations. For example, the phrase "processing or calculating based on a signal or generating an output result" in the present invention is not limited to the signal itself, but also includes, when necessary, performing voltage-to-current conversion, current-to-voltage conversion, and / or proportional conversion on the signal, and then processing or calculating based on the converted signal to generate an output result. Therefore, within the same spirit of the invention, those skilled in the art can conceive of various equivalent changes and combinations, and there are many ways to combine them, which will not be listed here. Therefore, the scope of the present invention should cover the above and all other equivalent changes.

Claims

1. A switch control circuit for controlling a path switch and a current sensing resistor connected in series between an input voltage and an output voltage, the switch control circuit comprising: An amplifier controls the gate voltage of the path switch based on the voltage drop across the current sensing resistor to enable a smooth start-up with current limiting. A slope detection circuit, coupled to the output voltage, is used to continuously monitor the rising slope of the output voltage; A pull-down switch is coupled between the gate of the path switch and an inhibit potential; When the slope detection circuit detects that the rising slope of the output voltage is lower than a preset slope threshold, it triggers the pull-down switch to turn on, thereby turning off the path switch.

2. The switch control circuit as described in claim 1, wherein, Also includes: A charge pump, after a smooth start-up, raises the gate voltage of the path switch to a high potential generated by the charge pump, thus fully turning on the path switch.

3. The switch control circuit as described in claim 1, wherein, The slope detection circuit includes: An analog-to-digital converter, coupled to the output voltage, converts the output voltage into a digital signal; A logic circuit calculates the rise slope of the output voltage based on the digital signal and compares it with a preset slope threshold to generate a control signal for controlling the pull-down switch.

4. The switch control circuit as described in claim 1, wherein, The switching control circuit allows the rise slope of the output voltage to be lower than the preset slope threshold within a preset time window, thereby achieving the debouncing function.

5. The switch control circuit as described in claim 1, wherein, When the rise rate of the output voltage is detected to be lower than the preset slope threshold and the path switch is turned off, the switch control circuit will attempt to start up smoothly again after a predetermined time delay.

6. The switch control circuit as described in claim 1, wherein, The switch control circuit counts and records the number of times a smooth start has been attempted again. When the number of attempts reaches a preset upper limit, the switch for that path remains off.

7. A switching circuit, comprising: A path switch and a current sensing resistor are connected in series between an input voltage and an output voltage; and The switch control circuit as described in any one of claims 1 to 6.

8. A method for controlling a path switch series coupled between an input voltage and an output voltage, the method comprising: Control the gate voltage of the path switch to smoothly start the output voltage in a current-limited manner; Continuously monitor the rising slope of this output voltage; The monitored upward slope will be compared with a preset slope threshold. When the upward slope is lower than the preset slope threshold, the path switch is turned off.

9. The method of claim 8, wherein, It also includes: during a smooth start-up process, allowing the rising slope to be lower than the slope threshold within a preset time window.

10. The method of claim 8, wherein, It also includes: after the path switch is turned off due to the rising slope being lower than the preset slope threshold, a predetermined time delay is allowed before attempting a smooth start again.

11. The method of claim 8, wherein, It also includes: counting and recording the number of times a smooth start has been attempted again; and keeping the path switch off when the number of attempts reaches a preset limit.

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