Datasheet

VIPER16 Power section
Doc ID 15232 Rev 5 13/25
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 20 Ω. It includes a SenseFET structure to
allow a 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 start up 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 7 on page 6); 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 VIPer16 is powered by the energy stored in the
V
DD
capacitor.
In 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 7 on page 6), delivering
I
DDch2
, see Table 7 on page 6 to the V
DD
capacitor during the MOSFET off time (see
Figure 21 on page 13).
The device can also be supplied through the auxiliary winding; in this 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 V
DDoff
threshold (see Table 7 on page 6).
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