Droop amplifier circuit
A droop amplifier circuit for a DC-DC regulator including an amplifier, at least one first resistive device, a second resistive device, a third resistive device, and a first capacitive device. Each first resistive device is coupled between an output inductor (phase node or current sense node) and the amplifier's non-inverting input. The first capacitive device is coupled between the regulator output and the amplifier's output. The second resistive device is coupled between the regulator output and the amplifier's inverting input. The third resistive device is coupled between the amplifier's inverting input and output. A second capacitive device may be coupled between the regulator output and the amplifier's non-inverting input. A fourth resistive device may be coupled in parallel with the second capacitive device. A relatively small, simple and low performing amplifier is sufficient. Circuit area and power are reduced, and low input offset voltage is more easily achieved.
1. A droop amplifier circuit for a DC-DC regulator with at least one output inductor coupled between a corresponding one of at least one phase node and an output, comprising:
an amplifier having an inverting input, a non-inverting input and an output;
at least one first resistive device, each for coupling between a corresponding output inductor and said non-inverting input of said amplifier;
a first capacitive device for coupling between the DC-DC regulator output and said output of said amplifier;
a second resistive device for coupling between the DC-DC regulator output and said inverting input of said amplifier; and
a third resistive device coupled between said inverting input and said output of said amplifier.
2. The droop amplifier circuit of claim 1 , wherein each of said at least one first resistive device is for coupling to a corresponding phase node of the DC-DC converter, further comprising a second capacitive device for coupling between the DC-DC regulator output and said non-inverting input of said amplifier.
3. The droop amplifier circuit of claim 2 , further comprising a fourth resistive device coupled in parallel with said second capacitive device.
4. The droop amplifier circuit of claim 2 , further comprising at least one fourth resistive device, each having a first end for coupling to an output terminal of a corresponding one of the at least one output inductor, and a second end forming an alternative output node coupled to said first and second capacitive devices and said second resistive device instead of the DC-DC regulator output.
5. The droop amplifier circuit of claim 1 , the DC-DC regulator including at least one current sense resistor coupled between a corresponding output inductor and the DC-DC regulator output, wherein each of said at least one first resistive device is for coupling to a corresponding current sense node.
6. The droop amplifier circuit of claim 5 , further comprising a fourth resistive device for coupling between said DC-DC regulator output and said non-inverting input of said amplifier.
7. The droop amplifier circuit of claim 5 , further comprising at least one fourth resistive device, each having a first end for coupling to an output terminal of a corresponding one of the at least one current sense resistor, and a second end forming an alternative output node coupled to said first capacitive device and said second resistive device instead of the DC-DC regulator output.
8. The droop amplifier circuit of claim 1 , wherein said amplifier comprises a low power amplifier.
9. The droop amplifier circuit of claim 1 , wherein said amplifier exhibits relatively low di/dt and dv/dt responses.
10. The droop amplifier circuit of claim 1 , wherein said amplifier comprises a transconductance amplifier with a high output impedance at high frequencies.
11. A multiphase DC-DC converter, comprising:
a plurality of switching circuits, each for switching an input voltage through a corresponding one of a plurality of output inductors via a corresponding one of a plurality of phase nodes based on a corresponding one of a plurality of pulse width modulation (PWM) signals to develop an output voltage at an output node;
control logic that monitors said output voltage and a droop voltage for developing said plurality of PWM signals; and
a droop circuit that provides said droop voltage, comprising:
an amplifier having an inverting input, a non-inverting input and an output that develops said droop voltage relative to said output node;
a plurality of first resistors, each coupled between a corresponding output inductor and said non-inverting input of said amplifier;
a first capacitor coupled between said output node and said output of said amplifier;
a second resistor coupled between said output node and said inverting input of said amplifier; and
a third resistor coupled between said inverting input and said output of said amplifier.
12. The multiphase DC-DC converter of claim 11 , wherein each of said plurality of first resistors is coupled to a corresponding phase node, further comprising a second capacitor coupled between said output node and said non-inverting input of said amplifier.
13. The multiphase DC-DC converter of claim 12 , further comprising a fourth resistor coupled in parallel with said second capacitor.
14. The multiphase DC-DC converter of claim 12 , further comprising a plurality of fourth resistors, each having a first end coupled to an output terminal of a corresponding one of said plurality of output inductors, and a second end forming an alternative output node coupled to said first and second capacitors and said second resistor instead of said output node.
15. The multiphase DC-DC converter of claim 11 , further comprising:
a plurality of current sense resistors, each coupled between a corresponding output inductor and said output node forming a plurality of current sense nodes each between a corresponding current sense resistor and a corresponding output inductor; and
wherein each of said plurality of first resistors is coupled to a corresponding one of said plurality of current sense nodes.
16. The multiphase DC-DC converter of claim 15 , further comprising a fourth resistor coupled between said output node and said non-inverting input of said amplifier.
17. The multiphase DC-DC converter of claim 15 , further comprising a plurality of fourth resistors, each having a first end coupled to an output terminal of a corresponding one of said plurality of current sense resistors, and a second end forming an alternative output node coupled to said first capacitor and said second resistor instead of said output node.
18. The multiphase DC-DC converter of claim 11 , wherein said amplifier comprises a low power amplifier.
19. The multiphase DC-DC converter of claim 11 , wherein said amplifier exhibits relatively low di/dt and dv/dt responses.
20. The multiphase DC-DC converter of claim 11 , wherein said amplifier comprises a transconductance amplifier with a high output impedance at high frequencies.