Pulse-Skip and Burst Mode

Part 20 · Voltage Regulation · page 3 of 3

Key point: light-load loss is mostly the switching events. Pulse-skip drops cycles. Burst groups them, then sleeps. VOUT moves about 10 mV inside the ±1% window.

5 V. Green band is 4.95–5.05 V. Blue is sleep or skip. η is a toy, not a datasheet.

1
30 mA burst already beats FCM.
IOUT 0.03 A, 250 kHz, 5 pulses, COUT 47 µF. Pulse-skip off. Sleep is 16.0 µs. ΔV is 10.2 mV. f_burst is 27.78 kHz. η sketch is 63.5 % against FCM 48.7 %.
2
Skip clocks instead of grouping them.
Tick Pulse-skip. Same 30 mA. One triangle, then three skipped cycles. f_eq is 63 kHz. ΔV is 7.7 mV. η sketch is 76.7 % against the same FCM 48.7 %.
3
More pulses spend the savings.
Pulse-skip off. 12 pulses per burst. Sleep is still 16.0 µs. f_eq rises to 187.5 kHz. η falls to 56.5 %. Extra edges ate the gain.
4
A bigger COUT sleeps longer.
5 pulses again. COUT 220 µF. Sleep is 72.0 µs. ΔV is 9.8 mV. f_burst is 10.87 kHz. η sketch is 80.8 %. The droop is still inside ±1 %.
5
10 mA makes the FCM gap wider.
IOUT 0.01 A, COUT 47 µF, 5 pulses. Sleep is 48.0 µs. ΔV is 10.2 mV. η is 51.5 % against FCM 24.0 %. The burst rate moved with the load. That moving rate is the EMI and audio complaint.

Real burst thresholds, spread-spectrum, and the compensation change between modes are not here. The numbers are a sketch.

Light load · skip vs burst

Burst: pulses lift VOUT ~10 mV, then sleep while it droops ~10 mV. Three packets on screen.

IOUT A fsw kHz Pulses /burst COUT µF

Pulse-skip

0 µs

iL · packets of switching, then sleep

VOUT · 5 V ±1% spec · ~10 mV burst/skip wiggle inside it

ΔV window—

t_sleep—

f_burst—

f_eq—

η sketch—

Green band is a ±1% window on 5 V (4.95–5.05 V). Burst/skip ripple is ~10 mV — still small in that spec.