Synthetic ripple regulator

• US 20050017703A1
• Filed: 05/25/2004
• Published: 01/27/2005
• Est. Priority Date: 09/06/2002
• Status: Active Grant

• Current Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Original Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Inventors: Walters, Michael M., Muratov, Vladimir, Wiktor, Sefan Wlodzimierz
• Granted Patent: US 7,132,820 B2
• Time in Patent Office: Days
• US Class Current: 323/288
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators

Abstract

A synthetic ripple regulator including a synthetic ripple voltage generator that generates a synthetic ripple voltage indicative of the ripple current through an output inductor. The regulator uses the synthetically generated ripple voltage to control toggling of a hysteretic comparator for developing the pulse width modulation (PWM) signal that controls switching of the regulator. In a non-limiting implementation, a transconductance amplifier monitors the phase node voltage of the inductor and supplies an inductor voltage-representative current to a ripple capacitor, which produces the synthetic ripple voltage. Using the replicated inductor current for ripple regulation results in low output ripple, input voltage feed forward, and simplified compensation.

Claims

1. A synthetic ripple voltage generator for a DC-DC regulator having a hysteretic comparator that develops a pulse width modulation (PWM) signal provided to a switching circuit that switches an input voltage via a phase node through an output inductor to develop an output voltage at an output node, said synthetic ripple voltage generator comprising:

a transconductance amplifier circuit having an input for coupling to the output inductor and an output for coupling to an input of the hysteretic comparator; and

a ripple capacitor coupled to said output of said transconductance amplifier circuit.

2. The synthetic ripple voltage generator of claim 1, wherein said transconductance amplifier circuit comprises a transconductance amplifier having a non-inverting input for coupling to the phase node and an inverting input for coupling to the output node.

3. The synthetic ripple voltage generator of claim 1, wherein said transconductance amplifier comprises a transconductance amplifier having a non-inverting input for coupling to the phase node and an inverting input for coupling to a reference voltage.

4. The synthetic ripple voltage generator of claim 1, wherein said ripple capacitor has a first end coupled to said output of said transconductance amplifier circuit and a second end for coupling to the output node.

5. The synthetic ripple voltage generator of claim 1, wherein said ripple capacitor has a first end coupled to said output of said transconductance amplifier circuit and a second end coupled to ground.

6. The synthetic ripple voltage generator of claim 1, further comprising a ripple resistor coupled to said ripple capacitor.

7. The synthetic ripple voltage generator of claim 6, further comprising:

a voltage source referenced to ground; and

said ripple resistor having a first end coupled to said ripple capacitor and a second end coupled to said voltage source.

8. The synthetic ripple voltage generator of claim 6, wherein said ripple resistor has a first end coupled to said ripple capacitor and a second end for coupling to the output node.

9. The synthetic ripple voltage generator of claim 1, wherein said transconductance amplifier circuit comprises:

a first transconductance amplifier having an input for coupling to the output node and an output coupled to said ripple capacitor to discharge said ripple capacitor based on the output voltage;

a second transconductance amplifier having an input for receiving the input voltage and an output; and

a switch circuit, having an input coupled to said output of said second transconductance amplifier, an output coupled to said ripple capacitor, and a control input for receiving the PWM signal, said switch circuit operative to couple said output of said second transconductance amplifier to said ripple capacitor to charge said ripple capacitor based on the input voltage upon initiation of PWM cycles.

10. A method of synthetically generating ripple voltage for a DC-DC regulator including a hysteretic comparator that develops a pulse width modulation (PWM) signal provided to a switching circuit that switches an input voltage via a phase node through an output inductor to develop an output voltage at an output node, said method comprising:

developing a ripple voltage indicative of current through the output inductor; and

applying the ripple voltage to an input of the hysteretic comparator.

11. The method of claim 10, wherein said developing a ripple voltage indicative of current through the output inductor comprises:

sensing voltage applied to the output inductor;

converting the sensed voltage to a sense current; and

charging a capacitive device with the sense current.

12. The method of claim 11, wherein said sensing voltage applied to the output inductor comprises sensing voltage at the phase node.

13. The method of claim 11, further comprising referencing the capacitive device to the output node.

14. The method of claim 11, further comprising referencing the capacitive device to ground.

15. The method of claim 11, further comprising coupling a resistive device to the capacitive device.

16. The method of claim 15, further comprising referencing the resistive device to the output node.

17. The method of claim 15, further comprising biasing the resistive device with a voltage source.

18. The method of claim 10, wherein said developing a ripple voltage indicative of current through the output inductor comprises:

converting the output voltage into a first current;

discharging a capacitive device with the first current;

converting the input voltage into a second current; and

charging the capacitive device with the second current upon initiation of each PWM cycle using the PWM signal.

19. The method of claim 10, wherein said developing a ripple voltage indicative of ripple current through the output inductor comprises:

sensing ripple current through the output inductor; and

converting sensed current into the ripple voltage.

20. A synthetic ripple regulator, comprising:

a hysteretic comparator having a first input and having an output that provides a pulse width modulation (PWM) signal;

a switching circuit that alternately couples a phase node to opposite polarities of an input voltage source based on said PWM signal;

an output inductor coupled between said phase node and an output node that develops a regulated output signal;

a transconductance amplifier circuit having an input coupled to said output inductor and an output coupled to said first input of said hysteretic comparator; and

a capacitor, coupled to said output of said transconductance amplifier circuit, that develops a ripple voltage indicative of current through said output inductor.

21. The synthetic ripple regulator of claim 20, further comprising an error amplifier having a first input receiving a reference voltage, a second input coupled to said output node, and an output coupled to a second input of said hysteretic comparator.

22. The synthetic ripple regulator of claim 20, wherein said transconductance amplifier circuit comprises a transconductor amplifier having a first input coupled to said phase node and a second input coupled to said output node.

23. The synthetic ripple regulator of claim 20, wherein said transconductance amplifier circuit comprises a transconductor amplifier having a first input coupled to said phase node and a second input coupled to a reference voltage.

24. The synthetic ripple regulator of claim 20, wherein said capacitor has a first end coupled to said output of said transconductance amplifier circuit and a second end coupled to said output node.

25. The synthetic ripple regulator of claim 20, wherein said capacitor has a first end coupled to said output of said transconductance amplifier circuit and a second end coupled to ground.

26. The synthetic ripple regulator of claim 20, further comprising:

a resistive device having a first end coupled to said output of said transconductance amplifier circuit and a second end; and

a voltage source coupled between said second end of said resistive device and ground.

27. The synthetic ripple regulator of claim 20, further comprising a resistive device having a first end coupled to said output of said transconductance amplifier circuit and a second end coupled to said output node.

28. The synthetic ripple regulator of claim 20, wherein said transconductance amplifier circuit comprises:

a first transconductance amplifier having an input coupled to said output node and an output coupled to said capacitor to discharge said capacitor based on said regulated output signal;

a second transconductance amplifier having an input coupled to said input voltage source and an output; and

a switch that couples said output of said second transconductance amplifier to said capacitor based on said PWM signal to charge said capacitor based on input voltage during portions of PWM cycles.