VIPER28 STMicroelectronics, VIPER28 Datasheet - Page 23

• Manufacturer Part Number: VIPER28
• Description: VIPerPlus family: fixed frequency high performance off line high voltage converter
• Manufacturer: STMicroelectronics

VIPER28
7.11
Burst-mode operation at no load or very light load
When the load decrease the feedback loop reacts lowering the feedback pin voltage. If it
falls down the burst mode threshold, V
switched on. After the MOSFET stops, as a result of the feedback reaction to the energy
delivery stop, the feedback pin voltage increases and exceeding the level, V
V
reported on
where power MOSFET is switching to period of time where power MOSFET is not switching;
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 from not
switching period where no power is processed. The advantage of burst mode operation is
an average switching frequency much lower then 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, I
Figure 26. Burst mode timing diagram, light load management
FBbmhys
V
FBbm
+V
V
FBbmhys
, the power MOSFET starts switching again. The burst mode thresholds are
V
I
COMP
DRAIN
I
FBbm
D_BM
I
I
I
DD
DD1
DD0
Table 8
and
Figure 30
Doc ID 15028 Rev 4
shows this behavior. Systems alternates period of time
FBbm
, the power MOSFET is not more allowed to be
Burst Mode
D_BM
, reported on
Table 8
Operation descriptions
.
FBbm
+
time
time
time
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