5 UCC25640X has Programmable Burst Mode Threshold

LED lighting PSU has dimming function to fine tune the output current to control the LED Flux, and the curve as Figure 5-1 showing.

If the LLC operates at burst mode, the output current is not continuing, then the LLC can cause the LED flicking so customer cannot let LLC operate at burst mode within the dimming range.

UCC25640X has LLSS pin to program the burst mode threshold by external resister divider to make this easy to use for customers to fine tune the burst mode threshold and also to disable the burst mode to force LLC continue switching even at no load is helpful to prevent LED flicking.

However, LED lighting PSU still needs the burst mode function to reduce the power consumption during the dimming off.

Same as previously mentioned, LED lighting PSU can control the output voltage to allow the LED to operate at dimming off condition to be able to turn off LED as the standby mode.

The burst mode threshold setting is also important for the dimming off condition and has some trade-off as below.

If the burst mode threshold sets too high, then the Vcc can be dropped to below UVLO threshold during the burst off time and can also allow the controller to operate at burst mode within dimming range.

If the burst mode threshold sets too low, the switching frequency increased and the switching loss increased also where this cannot meet the standby power consumption requirement.