Electronic device power protection circuitry

Patent metadata

Field	Value
Publication number	US-9329697-B2
Application number	US-201213629276-A
Country	US
Kind code	B2
Filing date	Sep 27, 2012
Priority date	Jun 15, 2012
Publication date	May 3, 2016
Grant date	May 3, 2016

Abstract

A host electronic device may be coupled to an accessory electronic device. During normal operation, the host device may supply the accessory device with power over a power supply line. Back-powering events in which the accessory device delivers power to the host device may be prevented by interposing a protection transistor in the power supply line. A current mirror may be formed using the protection transistor and an additional transistor that produces a sense current proportional to the amount of current that is flowing through the power supply line. A current-to-voltage amplifier may produce a sense voltage that is proportional to the sense current. A bias circuit may be used to bias the sense current through the current mirror. A control circuit may compare the sense voltage to one or more reference voltages and turn off the protection transistor when appropriate to prevent back-powering of the host device.

First claim

What is claimed is:

1. An electronic device configured to provide power to an accessory over a path that includes a power supply line, the electronic device comprising:
power regulator circuitry that provides a power supply voltage to the power supply line;
a first transistor interposed in the power supply line;
a second transistor, wherein the first and second transistors form a current mirror that produces a signal indicative of how much current is flowing through the first transistor; and
circuitry that provides a control signal to the first transistor to turn the first transistor off when the signal indicates that the current flowing through the first transistor is associated with a back-powering condition in which the electronic device is receiving power from the accessory.

2. The electronic device defined in claim 1 wherein the circuitry includes a control circuit that monitors a sense voltage that is proportional to the signal, wherein a voltage drop across the first transistor changes by a first amount in response to a given change in the current flowing through the first transistor, wherein the sense voltage changes by a second amount in response to the given change in the current flowing through the first transistor, and wherein the second amount is greater than the first amount.

3. The electronic device defined in claim 2 wherein the circuitry includes a current-to-voltage amplifier that converts the signal into the sense voltage.

4. The electronic device defined in claim 3 wherein the current-to-voltage amplifier comprises a pair of transistors coupled to form a common gate amplifier.

5. The electronic device defined in claim 4 wherein the control circuit comprises a comparator that receives the sense voltage and a reference voltage.

6. The electronic device defined in claim 1 wherein the first transistor has a first source, a first drain, and a first gate and wherein the second transistor has a second source, a second drain, and a second gate, the electronic device further comprising a bias circuit that biases the second drain to match a voltage on the first drain.

7. The electronic device defined in claim 6 wherein the current mirror includes a first line coupling the first source to the second source and includes a second line coupling the first gate to the second gate.

8. The electronic device defined in claim 1 wherein the circuitry is configured to assert the control signal to turn the first transistor on in response to determining that the current flowing through the first transistor is above a given threshold value and wherein the circuitry is configured to deassert the control signal to turn off the first transistor in response to determining that the current flowing through the second transistor is below the given threshold.

9. The electronic device defined in claim 8 wherein the given threshold has a negative value, wherein the control circuitry has a comparator with first and second inputs, and wherein the second input is configured to receive a reference voltage representative of the threshold.

10. The electronic device defined in claim 1 wherein the electronic device comprises a device selected from the group consisting of: a cellular telephone, a tablet computer, a portable computer, and a media player, the electronic device further comprising storage and processing circuitry.

11. A protection circuit in an electronic device that prevents power delivery to the electronic device from external equipment during a back-powering condition, the protection circuit comprising:
a first transistor coupled to a power supply input-output terminal, wherein a power supply current flows through the first transistor during at least some operations of the protection circuit;
a second transistor that is coupled to the first transistor to form a current mirror, wherein the current mirror produces a sense current that is proportional to the power supply current flowing through the first transistor; and
circuitry responsive to the sense current that provides a control signal to turn off the first transistor during the back-powering condition.

12. The protection circuit defined in claim 11 wherein the circuitry includes a current-to-voltage amplifier that converts the sense current to a sense voltage.

13. The protection circuit defined in claim 12 wherein the circuitry includes a control circuit that monitors the sense voltage and provides the control signal based on the sense voltage.

14. The protection circuit defined in claim 13 wherein the control circuit includes a comparator having a first input that receives the sense voltage and a second input that receives a reference voltage.

15. The protection circuit defined in claim 11 wherein the circuitry includes biasing circuitry that biases a drain voltage in the second transistor to match a drain voltage of the first transistor.

16. The protection circuit defined in claim 15 wherein the biasing circuitry includes a current source.

17. An electronic device comprising:
a first input-output terminal;
a second input-output terminal;
a ground power supply line coupled to the second input-output terminal;
a positive power supply line coupled to the first input-output terminal;
a first transistor coupled to the positive power supply line;
a second transistor that is coupled to the first transistor to form a current mirror, wherein the current mirror produces a sense current proportional to a current flowing through the first transistor and the positive power supply line; and
a current-to-voltage amplifier circuit that converts the sense current to a sense voltage.

18. The electronic device defined in claim 17 wherein the current-to-voltage amplifier comprises a resistor through which the sense current flows.

19. The electronic device defined in claim 18 further comprising a control circuit that receives the sense voltage and produces a corresponding control signal to control the first transistor.

20. The electronic device defined in claim 19 wherein the control circuit comprises a comparator having a first input that receives the sense voltage and a second input that receive a reference voltage, the electronic device further comprising a signal line, wherein the control signal is provided to a gate of the first transistor by the signal line.

21. An electronic device comprising:
a power supply terminal;
power regulator circuitry operable to supply power to external equipment through the power supply terminal;
protection circuitry coupled to the power supply terminal, wherein the protection circuitry is configured to detect a back-powering condition in which current is received by the electronic device at the power supply terminal and wherein the protection circuitry is further configured to electrically disconnect the power regulator circuitry from the power supply terminal in response to detecting the back-powering condition.

22. An electronic device configured to provide power to an accessory over a path that includes a power supply line, the electronic device comprising:
power regulator circuitry that provides a power supply voltage to the power supply line;
a first transistor interposed in the power supply line;
a second transistor, wherein the first and second transistors form a current mirror that produces a signal indicative of how much current is flowing through the first transistor;
bias circuitry coupled to the first and second transistors that provides a current bias for the second tra

Assignees

• Apple Inc

Inventors

• Paul Rajarshi
• Perez Yehonatan
• Hrinya Stephen J
• Shoykhet Eugene L

Classifications

• H02J7/667

  disconnection of loads if battery is not under charge, e.g. in vehicle if engine is not running · CPC title

• G06F3/02 Primary

  Input arrangements using manually operated switches, e.g. using keyboards or dials · CPC title

• H02H7/20

  for electronic equipment (for converters H02H7/10; for electric measuring instruments G01R1/36; for DC voltage or current semiconductor regulators G05F1/569; for amplifiers H03F1/52; for electronic switching circuits H03K17/08) · CPC title

• H02H3/18

  responsive to reversal of direct current · CPC title

• G05F3/02 Primary

  Regulating voltage or current · CPC title