High resolution digital diode emulator for DC-DC converters

• US 6,643,145 B1
• Filed: 07/26/2002
• Issued: 11/04/2003
• Est. Priority Date: 07/26/2002
• Status: Active Grant

• Current Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Original Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Inventors: Harrison, William Todd
• Primary Examiner(s): Vu, Bao Q.
• Application Number:
  US10/206,562
• Time in Patent Office: 466 Days
• Field of Search: 363/16, 363/56.01, 363/95, 363/97, 363/131
• US Class Current: 363/16
• CPC Class Codes: H02M 3/157 with digital control
• CPC Class Codes: H03F 2200/31 the switching power stage comprising circuitry for emulating the behaviour of a bootstrap diode

Abstract

A digital diode emulator (DDE) for a DC-DC converter increments a digital counter with a high frequency clock. For each inductor current cycle, the counter counts between turn-on and turn-off of the output switching circuit'"'"'s lower switch. When the contents of the counter match a modification of a count latched from the previous inductor current cycle, a turn-off signal is supplied to the control logic. If the previous inductor current cycle'"'"'s turn-off signal occurred late, the latched count is decremented by one bit. If the previous cycle'"'"'s turn-off signal occurs early, the latched count is incremented by one bit. Over successive inductor current cycles, the digital diode emulator effectively ‘dithers’ the turn-off time of the switching circuit'"'"'s lower switch about the zero-crossing point of the inductor current.

Claims

1. For use with a DC-DC voltage converter, having a controller which generates a switching signal, that switchably controls operation of a switching circuit, containing first and second electronic power switching devices coupled between respective power supply terminals, and having a common node thereof coupled through an inductor element to an output voltage terminal and a capacitor element, a method of digitally emulating diode operation of said switching circuit during off time of said switching signal, said method comprising the steps of:

(a) generating a switch-off signal for turning off said second electronic power switching device;

(b) sensing a digital state of a phase voltage at said common node;

(c) over successive cycles of said switching signal, adjusting the turn-off time of said switch-off signal based upon respective contents of a digital counter, the contents of which are successively modified by a clock signal having a frequency in excess of said switching signal, and in accordance with successively sensed digital states of said voltage at said common node.

2. The method according to claim 1, wherein step (c) comprises, wherein said controller is operative to turn on said second electronic power switching device in accordance with a first switching state of said switching signal, and to turn off said second electronic power switching device and turn on said first electronic power switching device in accordance with a second switching state of said switching signal.

3. The method according to claim 1, wherein step (c) comprises the steps of

(c1) for each cycle of said switching signal, causing said digital counter to count said clock signal from a prescribed attribute of said switching signal until said switch-off signal for turning off said second electronic power switching device, and thereby produce a count value,

(c2) storing said count value produced in step (c1), and

(c3) for a respective cycle of said switching signal, defining said turn-off time of said switch-off signal in accordance with a prescribed relationship between contents of said digital counter and said count value, as produced in step (c1) for an immediately previous cycle of said switching signal.

4. The method according to claim 3, wherein step (c3) includes, for said respective cycle of said switching signal, selectively modifying said count value, as stored in step (c2) for said immediately previous cycle of said switching signal, based upon whether the switch-off signal for turning off said second electronic power switching device during said immediately previous cycle of said switching signal occurred prior or subsequent to current through said inductor reaching zero, to produce a modified count value, and defining said turn-off time of said switch-off signal in response to said contents of said digital counter corresponding to said modified count value.

5. The method according to claim 3, wherein step (c3) comprises, for said respective cycle of said switching signal, selectively incrementing said count value, as stored in step (c2) for said immediately previous cycle of said switching signal, in response to the switch-off signal for turning off said second electronic power switching device during said immediately previous cycle of said switching signal having occurred prior to current through said inductor reaching zero, to produce an incremented count value, and defining said turn-off time of said switch-off signal in response to said contents of said digital counter corresponding to said incremented count value.

6. The method according to claim 3, wherein step (c3) comprises, for said respective cycle of said switching signal, selectively decrementing said count value, as stored in step (c2) for said immediately previous cycle of said switching signal, in response to the switch-off signal for turning off said second electronic power switching device during said immediately previous cycle of said switching signal having occurred subsequent to current through said inductor reaching zero, to produce a decremented count value, and defining said turn-off time of said switch-off signal in response to said contents of said digital counter corresponding to said decremented count value.

7. A digital diode emulator for a DC-DC voltage converter having a controller, which generates a switching signal that switchably controls operation of a switching circuit containing first and second electronic power switching devices coupled between respective power supply terminals, a common node thereof being coupled through an inductor element to an output voltage terminal and a capacitor, said digital diode emulator comprising:

a switch-off signal control circuit, which is operative to generate a turn-off signal for turning off said second electronic power switching device;

a turn-off signal controller, which is operative, over successive cycles of said switching signal, to adjust the turn-off time of said switch-off signal based upon respective contents of a digital counter, the contents of which are successively modified by a clock signal having a frequency in excess of said switching signal, and in accordance with successively sensed digital states of said voltage at said common node.

8. The digital diode emulator according to claim 7, wherein step switch-off signal control circuit is operative to turn on said second electronic power switching device in accordance with a first switching state of said switching signal, and to turn off said second electronic power switching device and turn on said first electronic power switching device in accordance with a second switching state of said switching signal.

9. The digital diode emulator according to claim 7, wherein said turn-off signal controller is operative, for each cycle of said switching signal, to cause said digital counter to count said clock signal from a prescribed attribute of said switching signal until said switch-off signal for turning off said second electronic power switching device, and thereby produce a count value, which is stored in a count memory, and wherein, for a respective cycle of said switching signal, said turn-off signal controller is operative to define said turn-off time of said switch-off signal, in accordance with a prescribed relationship between contents of said digital counter and said count value, as stored in said count memory for an immediately previous cycle of said switching signal.

10. The digital diode emulator according to claim 9, wherein said turn-off signal controller is operative, for said respective cycle of said switching signal, to selectively modify said count value, as stored in said count memory for said immediately previous cycle of said switching signal, based upon whether the switch-off signal for turning off said second electronic power switching device during said immediately previous cycle of said switching signal occurred prior or subsequent to current through said inductor reaching zero, to produce a modified count value, and to define said turn-off time of said switch-off signal in response to said contents of said digital counter corresponding to said modified count value.

11. The digital diode emulator according to claim 10, wherein said turn-off signal controller is operative, for said respective cycle of said switching signal, to selectively increment said count value, as stored in said count memory for said immediately previous cycle of said switching signal, in response to the switch-off signal for turning off said second electronic power switching device during said immediately previous cycle of said switching signal having occurred prior to current through said inductor reaching zero, to produce an incremented count value, and to define said turn-off time of said switch-off signal in response to said contents of said digital counter corresponding to said incremented count value.

12. The digital diode emulator-according to claim 10, wherein said turn-off signal controller is operative, for said respective cycle of said switching signal, to selectively decrement said count value, as stored in said count memory for said immediately previous cycle of said switching signal, in response to the switch-off signal for turning off said second electronic power switching device during said immediately previous cycle of said switching signal having occurred subsequent to current through said inductor reaching zero, to produce a decremented count value, and to define said turn-off time of said switch-off signal in response to said contents of said digital counter corresponding to said decremented count value.

13. In a diode emulator for a DC-DC voltage converter, having a controller which generates a switching signal, that switchably controls operation of a switching circuit, containing first and second electronic power switching devices coupled between respective power supply terminals, and having a common node thereof coupled through an inductor element to an output voltage terminal and a capacitor element, the improvement wherein said diode emulator includes:

a digital counter which, for each switching signal cycle, counts clock signals having a frequency higher than that of said switching signal between turn-on and turn-off of one of said first and second electronic power switching devices, and wherein, over successive switching signal cycles, contents of said digital counter are used to effectively ‘

dither’

the turn-off time of said one of said first and second electronic power switching devices about the zero-crossing point of current through said inductor current.

14. The improvement according to claim 13, wherein, a turn-off signal for said one of said first and second electronic power switching devices is generated in response to contents of said counter matching a modification of a count latched from the previous switching signal cycle.

15. The improvement according to claim 13, wherein said modification of said count is such that if the previous switching signal cycle'"'"'s turn-off signal occurred late, said count is decremented, whereas if the previous switching signal cycle'"'"'s turn-off signal occurs early, said count is incremented.