LOW DROP-OUT LINEAR REGULATOR INCLUDING A STABLE COMPENSATION METHOD AND CIRCUIT FOR PARTICULAR USE IN AUTOMOTIVE APPLICATIONS

Abstract

A compensated regulator includes a transconductance stage having a positive input for receiving a reference voltage, a negative input, and an output, an adjustable compensation block coupled between the output of the transconductance stage and ground, a feedback circuit having a first node coupled to the output of the compensated regulator, a second node coupled to the negative input of the transconductance stage, and a third node coupled to ground, and a driver stage having an input coupled to the output of the transconductance stage, a current output coupled to the output of the compensated regulator, and a sense output coupled to the adjustable compensation block.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned and other features and objects of the present invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of a preferred embodiment taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic diagram of a traditional regulator used in automotive applications, according to the prior art;

FIG. 2 is a schematic diagram of a regulator using the compensation circuit and method according to the present invention;

FIG. 3 is a plot of Req2 and Rzero with respect to load current of the compensated regulator of the present invention;

FIG. 4 is a plot of the ratio of Rzero to Req2 with respect to load current of the compensated regulator of the present invention;

FIG. 5 is a plot of the ratio of P2 to Z1 with respect to load current of the compensated regulator of the present invention;

FIG. 6 is a plot of the regulated output voltage and load transients with the output capacitor=0.1 uF and ESR=0 ohm according to the present invention;

FIG. 7 is a plot of the regulated output voltage and load transients with the output cap=0.1 uF and ESR=30 ohm according to the present invention;

FIG. 8 is a plot of the regulated output voltage and load transients with the output cap=100 uF and ESR=0 ohm according to the present invention; and

FIG. 9 is a plot of the regulated output voltage and load transients with the output cap=100 uF and ERS=30 ohm according to the present invention.

Claims

1. A compensation method for an electronic circuit comprising: providing a compensation block coupled to a node in the electronic circuit;sensing a load current of the electronic circuit; andadjusting the impedance of the compensation block in response to the value of the load current.

2. The compensation method of claim 1 wherein adjusting the impedance of the compensation block in response to the value of the load current comprises adjusting the resistance of a resistive portion of the compensation block.

3. The compensation method of claim 1 wherein providing a compensation block comprises providing a compensation block including a resistor in parallel connection with a current path of a transistor.

4. The compensation method of claim 3 wherein adjusting the impedance of the compensation block in response to the value of the load current comprises varying a gate voltage of the transistor.

5. The compensation method of claim 1 wherein sensing the load current of the electron circuit comprises providing a current sensing transistor in parallel with an output current driving transistor.

6. An electronic circuit comprising: a compensation block coupled to a node in the electronic circuit;means for sensing a load current of the electronic circuit; andmeans for adjusting the impedance of the compensation block in response to the value of the load current.

7. The electronic circuit of claim 6 wherein the means for adjusting the impedance of the compensation block in response to the value of the load current comprises an adjustable resistance in parallel with a resistor in the compensation block.

8. The electronic circuit of claim 6 wherein the compensation block comprises a resistor in parallel connection with a current path of a transistor.

9. The electronic circuit of claim 8 wherein the means for adjusting the impedance of the compensation block in response to the value of the load current comprises circuitry for varying a gate voltage of the transistor.

10. The electronic circuit of claim 6 wherein the means for sensing the load current of the electron circuit comprises a current sensing transistor in parallel with an output current driving transistor.

11. A compensated regulator comprising: a transconductance stage having a positive input for receiving a reference voltage, a negative input, and an output;an adjustable compensation block coupled between the output of the transconductance stage and ground;a feedback circuit having a first node coupled to the output of the compensated regulator, a second node coupled to the negative input of the transconductance stage, and a third node coupled to ground; anda driver stage having an input coupled to the output of the transconductance stage, a current output coupled to the output of the compensated regulator, and a sense output coupled to the adjustable compensation block.

12. The compensated regulator of claim 11, wherein the compensation block comprises a resistor.

13. The compensated regulator of claim 11, wherein the compensation block comprises a capacitor.

14. The compensated regulator of claim 11, wherein the compensation block comprises a resistor in parallel connection with the current path of a transistor.

15. The compensated regulator of claim 11, wherein the compensation block comprises: a first resistor;a second resistor in series connection with the first resistor; anda capacitor in series connection with the first and second resistors.

16. The compensated regulator of claim 15, wherein the compensation block further comprises a current mirror in parallel connection with the second resistor for receiving a sense current from the sense output, and for providing a variable resistance.

17. The compensated regulator of claim 16, wherein the compensation block further comprising a buffer stage coupled between the first and second resistors, and the current mirror.

18. The compensated regulator of claim 11, wherein the feedback circuit comprises a first resistor coupled between the first node and the second node, and a second resistor coupled between the second node and the third node.

19. The compensated regulator of claim 11, wherein the driver stage comprises an output current driving transistor.

20. The compensated regulator of claim 19 further comprising a current sensing transistor in parallel with the output current driving transistor.

21. A compensated regulator comprising: a compensation impedance that is variable with load current;a plurality of poles and zeros in a compensation loop;a first pole that moves in frequency with the value of the load current; anda first zero that moves in frequency with the value of the load current,wherein the movement in frequency of the first pole and first zero substantially tracks each other with respect to the value of the load current so that the first pole and the first zero are substantially canceled out over a range of load current values between about one microamp and one amp.