Datasheet

VIPER06 Power section
Doc ID 022794 Rev 1 15/28
7 Power section
The power section is implemented with an N-channel power MOSFET with a breakdown
voltage of 800 V min. and a typical R
DS(on)
of 32 Ω. It includes a SenseFET structure to allow
virtually lossless current sensing and the thermal sensor.
The gate driver of the power MOSFET is designed to supply a controlled gate current during
both turn-ON and turn-OFF in order to minimize common-mode EMI. During UVLO
conditions, an internal pull-down circuit holds the gate low in order to ensure that the power
MOSFET cannot be turned ON accidentally.
8 High voltage current generator
The high-voltage current generator is supplied by the DRAIN pin. At the first startup of the
converter it is enabled when the voltage across the input bulk capacitor reaches the
V
DRAIN_START
threshold, sourcing a I
DDch1
current (see Table 6 on page 7). As the V
DD
voltage reaches the V
DDon
threshold, the power section starts switching and the high-
voltage current generator is turned OFF. The VIPER06 is powered by the energy stored in
the V
DD
capacitor.
In a steady-state condition, if the self-biasing function is used, the high-voltage current
generator is activated between V
DDCSon
and V
DDon
(see Table 6 on page 7), delivering
I
DDch2
, see Table 6 on page 7 to the V
DD
capacitor during the MOSFET off-time (see
Figure 21).
The device can also be supplied through the auxiliary winding in which case the high-
voltage current source is disabled during steady-state operation, provided that VDD is
above V
DDCSon
.
At converter power-down, the V
DD
voltage drops and the converter activity stops as it falls
below the V
DDoff
threshold (see Table 6 on page 7).
Figure 21. Power-on and power-off
I
DD
V
DD
V
DRAIN
V
DDon
t
t
t
t
V
IN
V
DRAIN_START
t
t
Power-on
Power-off
Normal operation
regulation is lost here
V
IN
< V
DRAIN_START
HV startup is no more activated
With internal self-supply
Without internal self-supply
V
DDCSon
V
DDoff
I
DDch1
I
DDch2