進入Burst mode狀態

To further avoid acoustic noise, the circuit prevents the
burst frequency during skip mode from entering the audible
range by limiting it to a maximum of 800 Hz. This is
achieved via a timer tquiet that is activated during
Quiet−Skip. The start of the next burst cycle is prevented
until this timer has expired. As the output power decreases,
the switching frequency decreases. Once it hits minimum
switching frequency fOSC(min), the skip−in threshold is
reached and burst mode is entered − switching stops as soon
as the current drive pulses ends – it does not stop
immediately