Boost spread-spectrum technique in pulse skip mode with fixed frequency clock reference
A boost DC-DC switching converter architecture is provided, with a spread spectrum technique working in pulse skip mode, and a fixed frequency clock reference, comprising a high side switch and a low side switch, controlled by a voltage or current mode control loop operating in a Pulse Width Modulation (PWM) mode, and having a pulse skip mode. The switching converter comprises an inductor, connected between an input voltage terminal and the high side switch, and also connected to the low-side switch, and a random delay generator, where the random delay generator randomly varies a time for entering, or exiting, or both entering and exiting pulse skip mode, and varies a time where the high side switch is turned off in pulse skip mode.
1. A boost DC-DC switching converter with fixed frequency input clock reference and spread spectrum technique in pulse skip mode, comprising:
a high side switch and a low side switch, configured to be controlled by a voltage or current control mode loop operating in a PWM (Pulse Width Modulation) mode, and having a pulse skip mode;
an inductor connected between an input voltage terminal and said high side switch, and also connected to said low-side switch; and
a random delay generator,
wherein said switching converter is configured to evaluate during each clock cycle whether to resume said PWM mode, or to continue said pulse skip mode, and to randomly vary a time for turning off said high side switch after entering said pulse skip mode, using said random delay generator, such that a time between two consecutive PWM bursts is randomized, between a minimum and maximum value, and wherein a randomly varying a time for exiting said pulse skip mode comprises randomizing a time between PWM operations between a minimum and maximum value, by randomizing a difference between an internally generated reference time pulse and a minimum on time of said converter, to exit said pulse skip mode.
2. The switching converter of claim 1 , wherein said random delay generator is configured to randomly vary a time for entering said pulse skip mode.
3. The switching converter of claim 2 , wherein said time for entering said pulse skip mode is configured to be a minimum on time of said switching converter.
4. The switching converter of claim 1 , wherein said random delay generator is configured to randomly vary a time for entering and a time for exiting said pulse skip mode.
5. The switching converter of claim 1 , wherein said switching converter is configured to randomly vary a time for entering, or exiting, or entering and exiting said pulse skip mode, and said time for turning off said high side switch after entering said pulse skip mode, every time said pulse skip mode is about to be entered.
6. The switching converter of claim 1 , wherein said switching converter is configured to randomly vary a time for entering, or exiting, or entering and exiting said pulse skip mode, less often than every time said pulse skip mode is about to be entered, with a configurable frequency.
7. The switching converter of claim 1 , wherein said pulse skip mode is configured to trigger if a duty-cycle falls below a certain threshold.
8. The switching converter of claim 1 , wherein said switching converter is configured to exit said pulse skip mode if a duty-cycle is higher than said internally generated reference time pulse.
9. The switching converter of claim 1 , further comprising an input capacitor configured across said input voltage terminal and ground.
10. The switching converter of claim 1 , further comprising an output capacitor configured across an output voltage terminal and ground.
11. The switching converter of claim 1 , wherein said inductor is connected between said input voltage terminal and said output voltage terminal when said high side switch is closed, and connected between said input voltage terminal and ground when said low side switch is closed.
12. The switching converter of claim 1 , wherein said random delay generator is configured to provide a time to exit said pulse skip mode, and to provide a time to turn off said high side switch in pulse skip mode, and to provide a minimum on time of said switching converter.
13. The switching converter of claim 1 , wherein said switching converter is configured to maintain a phase relationship with other DC-DC switching converters in a system using a fixed frequency reference clock.
14. The switching converter of claim 1 , wherein said high side switch is a NMOS or PMOS device.
15. The switching converter of claim 1 , wherein said low side switch is a NMOS device.
16. The switching converter of claim 1 , wherein said random delay generator comprises a linear feedback shift register (LFSR).
17. The switching converter of claim 1 , wherein said random delay generator comprises digital programmable delay blocks driven by a random code generator.
18. The switching converter of claim 1 , wherein said random delay generator comprises a variable ramp and comparator, wherein said variable ramp employs a programmable capacitor driven by a random code generator.
19. A method for spreading harmonic content of a boost DC-DC switching converter output, comprising the steps of:
operating said boost DC-DC switching converter in a PWM (Pulse Width Modulation) mode;
operating said boost DC-DC switching converter in a pulse skip mode;
evaluating during each clock cycle whether to resume said PWM mode, or to continue said pulse skip mode; and
randomly varying a time to turn off a high side switch during said pulse skip mode, such that a time between two consecutive PWM bursts is randomized, between a minimum and maximum value,
and wherein a time for exiting said pulse skip mode is a randomized time between PWM operations between a minimum and maximum value, determined by a difference between an internally generated reference time pulse and a minimum on time of said converter, to exit said pulse skip mode.
20. The method of claim 19 , wherein a time for entering said pulse skip mode is randomly varied.
21. The method of claim 20 , wherein said time for entering said pulse skip mode is a minimum on time of said switching converter.
22. The method of claim 19 , wherein a time for entering and a time for exiting said pulse skip mode is randomly varied.
23. The method of claim 19 , wherein a random delay generator randomly varies a time for entering, or exiting, or entering and exiting said pulse skip mode, and said time for turning off said high side switch during said pulse skip mode, every time said pulse skip mode is about to be entered.
24. The method of claim 19 , wherein said random delay generator randomly varies a time for entering, or exiting, or entering and exiting said pulse skip mode, less often than every time said pulse skip mode is about to be entered, with a configurable frequency.
25. The method of claim 19 , wherein said pulse skip mode triggers if a duty-cycle falls below a certain threshold.
26. The method of claim 19 , wherein said switching converter exits said pulse skip mode if a duty-cycle is higher than said internally generated reference time pulse.
27. The method of claim 23 , wherein said random delay generator provides a time to exit said pulse skip mode, and provides a time to turn off said high side switch in pulse skip mode, and provides a minimum on time of said switching converter.
28. The method of claim 19 , wherein said switching converter maintains a phase relationship with other DC-DC switching converters in a system using a fixed frequency reference clock.