VIPER35 datasheet(35/44 Pages) STMICROELECTRONICS

35 / 44 page

DocID026980 Rev 4

35/44

VIPer35

Operation description

Figure 41. Timing diagram: overload protection

8.14

Burst mode operation at no-load or very light load

When the load decreases, the feedback loop lowers the feedback pin voltage. If it falls down

the burst mode threshold, VFBBm, the power MOSFET doesn’t switch on. After the MOSFET

stops, the feedback pin voltage increases and by exceeding the level, VFBbm + VFBbmhys,

the power MOSFET starts switching again. The burst mode thresholds are reported in

Table 7 and Figure 42 shows this behavior. System alternates period of time where power

MOSFET switches to period of time where power MOSFET doesn’t switch; this device

working mode is the burst mode. The power delivered to output during switching periods

exceeds the load power demands; the excess of power is balanced by the period where no

power is processed. The advantage of burst mode operation is an average switching

frequency much lower than the normal operation working frequency, up to some hundred of

hertz, minimizing all frequency-related losses. During the burst mode the drain current peak

is clamped to the level, ID_BM, (see Table 7).

VIPER35 Fiches technique(PDF) 35 Page - STMicroelectronics