Pulse frequency operation of regulated charge pumps

• US 6,169,444 B1
• Filed: 07/15/1999
• Issued: 01/02/2001
• Est. Priority Date: 07/15/1999
• Status: Expired due to Term

• Current Assignee: Maxim Integrated Products, Inc. (Analog Devices, Inc.)
• Original Assignee: Maxim Integrated Products, Inc. (Analog Devices, Inc.)
• Inventors: Thurber, Charles R. Jr.
• Primary Examiner(s): KIM, JUNG H
• Application Number:
  US09/354,924
• Time in Patent Office: 537 Days
• Field of Search: 327/536, 327/538, 327/540, 327/541, 327/543, 327/537, 363/60
• US Class Current: 327/536
• CPC Class Codes: H02M 1/0041 Control circuits in which a clock signal is selectively enabled or disabled
• CPC Class Codes: H02M 3/07 using capacitors charged and discharged alternately by semiconductor devices with control electrode , e.g. charge pumps

Abstract

A regulating system (10) for a charge pump (12) employing a detection sub-circuit (28) and an enable sub-circuit (30) to operate an oscillator (26) and a channel-switching sub-circuit (32) in an automatic manner producing many of the advantages of previously unreconcilable skip mode and constant frequency mode type regulation. The detection sub-circuit (28) compares a feedback signal (52) from the output terminal (18) of the charge pump (12) to a reference signal (56) and produces an error signal (42) representative of output voltage deviation. Concurrently, the enable sub-circuit (30) compares a threshold signal (72) set for a minimum energy quanta which it is efficient for the flying capacitor (24) of the charge pump (12) to transfer to the error signal (42) and produces an enable signal (38) to enable the oscillator (26). An oscillator signal (40) then controls switching within the channel-switching sub-circuit (32) to set when the energy quanta are transferred and the error signal (42) further is used to control resistance in the charge path to the flying capacitor (24) to set the magnitude of the quanta.

Claims

1. A circuit for regulating a charge pump receiving an input signal across an input terminal and a common terminal and producing an output signal across an output terminal and the common terminal, wherein the input signal has an input voltage and the output signal has an output voltage and the charge pump includes an input capacitor connected across the input terminal and the common terminal, and an output capacitor connected across the output terminal and the common terminal, and a flying capacitor having a first side and a second side, the circuit comprising:

an oscillator which, when enabled by an enable signal, produces an oscillator signal that alternates between a first state and a second state;

a detection sub-circuit producing an error signal when the output voltage deviates from a desired output voltage, wherein said error signal has voltage representative of how much the output voltage differs from said desired output voltage;

a channel-switch sub-circuit suitable for connecting the flying capacitor across the common terminal and the input terminal when said oscillator signal is in said first state, and alternately connecting the flying capacitor across the common terminal and the output terminal when said oscillator signal is in said second state;

said channel-switch sub-circuit further suitable for controllably setting resistance to the flying capacitor responsive to voltage in said error signal when said oscillator signal is in said first state; and

an enable sub-circuit producing said enable signal when said error signal has voltage exceeding said desired output voltage by a preset amount, for regulating the charge pump by enabling said oscillator to operate said channel-switch sub-circuit to alternately charge the flying capacitor at a rate controlled by resistance set by said channel-switch sub-circuit from the input terminal and to discharge the flying capacitor via the output terminal into the output capacitor.

2. The circuit of claim 1, wherein said detection sub-circuit includes:

a reference unit suitable for producing a reference signal having said desired output voltage; and

an error comparator suitable for producing said error signal when said output voltage differs from said desired output voltage.

3. The circuit of claim 1, wherein said detection sub-circuit includes:

a voltage divider connected across said output terminal and said common terminal, wherein said voltage divider produces a feedback signal having voltage related to the output voltage;

a reference unit suitable for producing a reference signal having voltage related to said desired output voltage; and

an error comparator suitable for producing said error signal when a relationship between said feedback signal and said reference signal indicates that the output voltage differs from said desired output voltage.

4. The circuit of claim 1, wherein:

said channel-switch sub-circuit connects the first side of the flying capacitor to the common terminal and the second side of the flying capacitor to the input terminal when said oscillator signal is in said first state; and

said channel-switch sub-circuit alternately connects the first side of the flying capacitor to the input terminal and the second side of the flying capacitor to the output terminal when said oscillator signal is in said second state, to operate the charge pump such that the output voltage produced is of same polarity and of higher value than the input voltage received by the charge pump.

5. The circuit of claim 1, wherein:

said channel-switch sub-circuit connects the first side of the flying capacitor to the common terminal and the second side of the flying capacitor to the input terminal when said oscillator signal is in said first state; and

said channel-switch sub-circuit alternately connects the first side of the flying capacitor to the output terminal and the second side of the flying capacitor to the common terminal when said oscillator signal is in said second state, to operate the charge pump such that the output voltage produced is of opposite polarity and of lower value than the input voltage received by the charge pump.

6. The circuit of claim 1, wherein:

the first side of the flying capacitor is connected to the common terminal;

said channel-switch sub-circuit connects the second side of the flying capacitor to the input terminal when said oscillator signal is in said first state; and

said channel-switch sub-circuit alternately connects the second side of the flying capacitor to the output terminal when said oscillator signal is in said second state, to operate the charge pump such that the output voltage produced is of same polarity and of lower value than the input voltage received by the charge pump.

7. The regulated charge pump of claim 1, wherein said enable sub-circuit includes:

a resistance series connected with a replica device at a node and together connected across the input terminal and the common terminal such that a threshold signal is produced at said node; and

an enable comparator suitable for producing said enable signal when voltage in said error signal is greater than voltage in said threshold signal.

8. The circuit of claim 5, wherein said replica unit is a diode connected device.

9. The circuit of claim 6, wherein said diode connected device is a MOSFET transistor with gate and drain connected together.

10. The circuit of claim 1, wherein said channel sub-circuit includes at least one n-channel MOSFET transistor.

11. The circuit of claim 1, wherein said switch sub-circuit is a plurality of transistors operating in a double pole single throw manner.

12. A method for regulating a charge pump receiving an input signal having an input voltage and producing an output signal having an output voltage, wherein the charge pump is of the type having an input capacitor connected across an input terminal and a common terminal, an output capacitor connected across an output terminal and the common terminal, and a flying capacitor having a first side and a second side, the method comprising the steps of:

(a) producing an error signal when the output voltage of the charge pump deviates from a desired output voltage;

(b) comparing said error signal with a desired enable threshold to produce an enable signal when said error signal exceeds said desired enable threshold;

(c) enabling an oscillator, responsive to presence of said enable signal, to produce an oscillator signal alternating between a first state and a second state;

(d) charging the flying capacitor from the input terminal of the charge pump when said oscillator signal is in said first state and discharging the flying capacitor into the output capacitor when said oscillator signal is in said second state;

(e) setting a resistance, responsive to magnitude of said error signal, controlling at what rate the flying capacitor charges and discharges, thereby regulating the charge pump.

13. The method of regulating of claim 12, wherein said step (a) includes:

producing a feedback signal having voltage related to the output voltage;

producing a reference signal having voltage related to said desired output voltage; and

comparing said feedback signal to said reference signal, to produce said error signal when the output voltage is less than said desired output voltage.

14. The method of regulating of claim 12, wherein said step (b) includes:

producing a threshold signal having magnitude representative of a minimum level for efficient operation of the charge pump; and

comparing said threshold signal to said error signal, to produce said enable signal when said error signal exceeds said desired enable threshold.

15. The method of regulating of claim 12, wherein said step (d) includes:

switching connection of the first side of the flying capacitor to the common terminal and the second side of the flying capacitor to the input terminal when said oscillator signal is in said first state, to charge the flying capacitor; and

switching connection of the first side of the flying capacitor to the input terminal and the second side of the flying capacitor to the output terminal when said oscillator signal is in said second state, to discharge the flying capacitor such that the charge pump operates to produce the output voltage of same polarity and of higher value than the input voltage received by the charge pump.

16. The method of regulating of claim 12, wherein said step (d) includes:

switching connection of the first side of the flying capacitor to the common terminal and the second side of the flying capacitor to the input terminal when said oscillator signal is in said first state, to charge the flying capacitor; and

switching connection of the first side of the flying capacitor to the output terminal and the second side of the flying capacitor to the common terminal when said oscillator signal is in said second state, to discharge the flying capacitor such that the charge pump operates to produce the output voltage of opposite polarity and of lower value than the input voltage received by the charge pump.

17. The method of regulating of claim 12, wherein said step (d) includes:

connecting the first side of the flying capacitor to the common terminal;

switching connection of the second side of the flying capacitor to the input terminal when said oscillator signal is in said first state, to charge the flying capacitor; and

switching connection of the second side of the flying capacitor to the output terminal when said oscillator signal is in said second state, to discharge the flying capacitor such that the charge pump operates to produce the output voltage of same polarity and of lower value than the input voltage received by the charge pump.

18. The method of regulating of claim 12, wherein said step (d) includes:

determining whether the input voltage is lower or higher than said desired output voltage;

if the input voltage is lower than said desired output voltage, then;

switching connection of the first side of the flying capacitor to the common terminal and the second side of the flying capacitor to the input terminal when said oscillator signal is in said first state, to charge the flying capacitor; and

switching connection of the second side of the flying capacitor to the output terminal when said oscillator signal is in said second state, to discharge the flying capacitor such that the charge pump operates to produce the output voltage of same polarity and of lower value than the input voltage received by the charge pump; and

if the input voltage is higher than said desired output voltage, then;

switching connection of the first side of the flying capacitor to the common terminal and the second side of the flying capacitor to the input terminal when said oscillator signal is in said first state, to charge the flying capacitor; and

switching connection of the first side of the flying capacitor to the input terminal and the second side of the flying capacitor to the output terminal when said oscillator signal is in said second state, to discharge the flying capacitor such that the charge pump operates to produce the output voltage of same polarity and of higher value than the input voltage received by the charge pump.

19. The method of regulating of claim 12, wherein said step (e) includes setting said resistance by controllably biasing at least one transistor to control charging current to the flying capacitor.

20. The method of regulating of claim 19, wherein at least one said transistor is of an n-channel MOSFET type.