System and Method for Controlling a Hysteretic Mode Converter

• US 20080252278A1
• Filed: 12/06/2007
• Published: 10/16/2008
• Est. Priority Date: 12/06/2006
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Lindeberg, Jonne Jalmar Sebastian, Konnail, George Vincent, Iliasevitch, Stepan
• Granted Patent: US 7,777,470 B2
• Time in Patent Office: Days
• US Class Current: 323/283
• CPC Class Codes: H02M 1/0012 Control circuits using digital or numerical techniques in DC/DC converters H02M3/157, H02M3/33515; in DC-AC converters H02M7/53873
• CPC Class Codes: H02M 3/1563 without using an external clock H02M3/158 takes precedence

Abstract

A system and method for controlling a conversion frequency of a hysteretic mode voltage converter. A digital control loop comprises a timing measure unit having a first input coupled to a reference clock and a second input coupled to a clock based on a switching of the switching of the converter, and an on time adjust unit coupled to the timing measure unit. The timing measure unit counts a number of clock ticks of a clock signal provided by the clock occurring during a period of time specified by a number of clock ticks of a reference clock signal provided by the reference clock. The on time adjust unit adjusts an on time control signal based on the count of the number of clock ticks of the clock signal to alter a frequency of the switching.

Claims

1. A digital control loop for a switching converter, the digital control loop comprising:

a timing measure unit having a first input coupled to a reference clock and a second input coupled to a clock based on a switching of the switching of the converter, the timing measure unit to count a number of clock ticks of a clock signal provided by the clock occurring during a period of time specified by a number of clock ticks of a reference clock signal provided by the reference clock; and

an on time adjust unit coupled to the timing measure unit, the on time adjust unit to adjust an on time control signal based on the count of the number of clock ticks of the clock signal to alter a frequency of the switching.

2. The digital control loop of claim 1, wherein the timing measure unit comprises:

a reference counter coupled to the reference clock, the reference counter to count clock ticks in the reference clock signal;

a comparator coupled to the reference counter, the comparator to compare the count of the reference counter against a specified value;

a clock counter coupled to the clock, the clock counter to count clock ticks in the clock signal; and

a capture circuit coupled to an output of the comparator and to the clock counter, the capture circuit to store the count of the clock counter.

3. The digital control loop of claim 2, wherein the reference clock signal is provided by a high precision clock source.

4. The digital control loop of claim 1, wherein the on time adjust unit comprises:

a logic block configured to produce at an output an adjustment to the on time control signal based on the count of clock ticks of the clock signal; and

an adder coupled to the output of the logic block and an output of the on time adjust unit, the adder to combine the adjustment to the on time control signal and a current value of the on time control signal into a new value of the on time control signal.

5. The digital control loop of claim 4, wherein the adjustment to the on time control signal is further based on the current value of the on time control signal.

6. The digital control loop of claim 4, wherein the adjustment to the on time control signal either increases or decreases the frequency of the switching.

7. The digital control loop of claim 1, wherein the clock signal in an output of a comparator comparing a voltage drop across a load of the switching converter and a reference voltage.

8. The digital control loop of claim 7, wherein the comparator is a hysteretic comparator.

9. A switching converter comprising:

a first energy storing device coupled to a voltage input;

a second energy storing device coupled to the first energy storing device;

a switch coupled to the first energy storing device, the switch to selectively couple the first energy storing device to a power rail; and

a switch timing control unit coupled to the switch, the switch timing control unit configured to set a state of the switch to couple and decouple the first energy storing device to the power rail, wherein the state of the switch is based on a desired switching frequency of the switching converter.

10. The switching converter of claim 9, wherein the switch timing control unit comprises:

a hysteretic comparator having a first input coupled to a voltage reference and a second input coupled to a load coupled to the switching converter, the hysteretic comparator to produce a signal at an output based on a relationship between voltage levels of signals at the first input and the second input;

a timing loop having a first input coupled to a reference clock and a second input coupled to an output of the hysteretic comparator, the timing loop configured to determine a switching frequency of the switch changing state and to produce a control signal to set the switching frequency to be substantially equal to the desired switching frequency; and

a logic unit coupled to the timing loop and to the switch, the logic unit configured to generate a signal to set a state of the switch based on the control signal.

11. The switching converter of claim 10, wherein the switch timing control unit further comprises an on time control unit coupled in between the timing loop and the logic unit, the switch timing control unit configured to alter a charging current or a number of charging capacitors based on the control signal.

12. The switching converter of claim 9, wherein the timing loop comprises:

a timing measure unit having a first input coupled to the reference clock and a second input coupled to the output of the hysteretic comparator, the timing measure unit to count a number of clock ticks of a signal provided by the output of the hysteretic comparator occurring during a period of time specified by a number of clock ticks of a reference clock signal provided by the reference clock; and

an on time adjust unit coupled to the timing measure unit, the on time adjust unit to adjust an on time control signal based on the count of the number of clock ticks of the clock signal to alter a frequency of the switching.

13. The switching converter of claim 12, wherein the reference clock signal has a frequency that is greater than the desired switching frequency.

14. The switching converter of claim 9, wherein the switch couples the first energy storing device to electrical ground and the switching converter is a boost mode switching converter.

15. The switching converter of claim 9, wherein the switch couples the first energy storing device to the voltage input and the switching converter is a buck mode switching converter.

16. A method for adjusting a switching frequency of a switching converter, the method comprising:

counting a number of state switches of a switch in the switching converter occurring within a specified time period, wherein the number of state switches is related to the switching frequency;

decreasing the switching frequency in response to a determining that the count is greater than a first threshold;

increasing the switching frequency in response to a determining that the count is less than a second threshold; and

maintaining the switching frequency in response to a determining that the count is between the first threshold and the second threshold.

17. The method of claim 16, wherein the counting comprises:

starting a reference clock counter to count a number of clock ticks of a reference clock;

starting a switch counter to count the number of state switches; and

stopping the switch counter in response to a determining that the count of clock ticks of the reference clock is equal to a specified value.

18. The method of claim 16, wherein the decreasing comprises increasing a value of a control signal used to specify the switching frequency in response to a determining that the value is less than a high value threshold.

19. The method of claim 16, wherein the increasing comprises decreasing a value of a control signal used to specify the switching frequency in response to a determining that the value is greater than a low value threshold.

20. The method of claim 16, wherein the first threshold and the second threshold span a count of the number of switches when the switch is switching at a desired switching frequency.