Current Detection and Limiting Method and Apparatus

• US 20100157498A1
• Filed: 12/22/2008
• Published: 06/24/2010
• Est. Priority Date: 12/22/2008
• Status: Active Grant

• Current Assignee: Synaptics Incorporated
• Original Assignee: Conexant Systems Incorporated (Synaptics Incorporated)
• Inventors: Patel, Ketan B., Crespi, Lorenzo, Skov, James
• Granted Patent: US 8,274,772 B2
• Time in Patent Office: Days
• US Class Current: 361/93.900
• CPC Class Codes: G06F 1/266 Arrangements to supply power to external peripherals either directly from the computer or under computer control, e.g. supply of power through the communication port, computer controlled power-strips
• CPC Class Codes: G06F 2213/0042 Universal serial bus [USB]
• CPC Class Codes: H02H 9/02 responsive to excess current current limitation for voltage regulators G05F1/573; disconnection after limiting H02H3/025

Abstract

An apparatus for detecting and controlling current. A current detector for generating a first value that represents an amount of current being delivered to a device. A current limit circuit for generating a second value that represents a maximum permitted current level from a current source. A current controller for controlling the amount of current drawn by the device if the first value exceeds the second value.

Claims

1. An apparatus for detecting and controlling current comprising:

a current detector for generating a first value that represents an amount of current being delivered to a device;

a current limit circuit for generating a second value that represents a maximum permitted current level from a current source; and

a current controller for controlling the amount of current drawn by the device if the first value exceeds the second value.

2. The apparatus of claim 1 wherein the first value is generated by a voltage drop across a resistor that is in line with the current being delivered to the device.

3. The apparatus of claim 1 wherein the current limit circuit comprises:

a resistor having a predetermined value; and

a bias current source coupled to the resistor, the bias current source providing a predetermined current.

4. The apparatus of claim 1 wherein the current controller for controlling the amount of current drawn by the device if the first value exceeds the second value comprises a gain control for controlling a gain of a pre-amplifier

5. The apparatus of claim 1 wherein the current limit circuit comprises:

a resistor having a predetermined value;

a first bias current source coupled to the resistor, the first bias current source providing a first predetermined current;

a second bias current source coupled to the resistor, the second bias current source providing a second predetermined current; and

a switch for disconnecting the second bias current source if the first value exceeds the second value.

6. The apparatus of claim 5 further comprising circuitry for reconnecting the second bias current source if the first value is lower than a third value.

7. The apparatus of claim 1 further comprising a second current controller for disconnecting the device if the first value exceeds a third value.

8. The apparatus of claim 1 wherein the current detector for generating the first value that represents the amount of current being delivered to the device comprises means for generating the first value that represents the amount of current being delivered to the device.

9. The apparatus of claim 1 wherein the current limit circuit for generating the second value that represents the maximum permitted current level from the current source comprises means for generating the second value that represents the maximum permitted current level from the current source.

10. The apparatus of claim 1 wherein the current controller for controlling the amount of current drawn by the device if the first value exceeds the second value comprises means for controlling the amount of current drawn by the device if the first value exceeds the second value.

11. An apparatus for detecting and controlling current comprising:

a current detector for generating a first value that represents an amount of current being delivered to a device;

a current limit circuit for generating a second value that represents a maximum permitted current level from a current source, the current limit circuit comprising;

a resistor having a predetermined value;

a first bias current source coupled to the resistor, the first bias current source providing a first predetermined current;

a second bias current source coupled to the resistor, the second bias current source providing a second predetermined current;

a switch for disconnecting the second bias current source if the first value exceeds the second value; and

circuitry for reconnecting the second bias current source if the first value is lower than a third value;

a current controller for controlling the amount of current drawn by the device if the first value exceeds the second value, comprising a gain control for controlling a gain of a pre-amplifier;

a second current controller for disconnecting the device if the first value exceeds a third value; and

wherein the first value is generated by a voltage drop across a resistor that is in line with the current being delivered to the device.

12. A method for detecting and controlling current comprising:

generating a first voltage from a sense resistor in line with a current being provided to a device;

generating a second voltage from a reference resistor in line with a bias current source; and

generating a control signal to reduce the current being provided to the device if the first voltage is greater than the second voltage.

13. The method of claim 12 further comprising reducing a bias current of the bias current source after generating the control signal.

14. The method of claim 13 further comprising:

generating a third voltage from the reference resistor and the reduced bias current; and

terminating the generation of the control signal to reduce the current being provided to the device if the first voltage is less than the third voltage.

15. The method of claim 13 further comprising:

generating a third voltage from a second reference resistor in line with a second bias current source; and

generating a control signal to disable the device if the first voltage is greater than the third voltage.

16. The method of claim 12 further comprising:

reducing a bias current of the bias current source after generating the control signal; and

increasing the bias current if the first voltage is less than a third voltage.

17. The method of claim 12 further comprising:

reducing a bias current of the bias current source after generating the control signal;

generating a third voltage from the reference resistor and the reduced bias current;

terminating the generation of the control signal to reduce the current being provided to the device if the first voltage is less than the third voltage; and

increasing the bias current if the first voltage is less than the third voltage.