VIPER16LDTR Datasheet, PDF (13/25 Pages) STMicroelectronics – Fixed frequency VIPerTM plus family

VIPER16
7
Power section
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
V_IN
V_{DRAIN_START}
V_DD
V_DDon
V_DDCSon
V_DDoff
V_DRAIN
With internal self-supply
Without internal self-supply
V_IN < V_{DRAIN_START}
HV startup is no more activated
regulation is lost here
t
t
I_DD
I_DDch2
I_DDch1
Power-on
Normal operation
t
Power-off
t
Doc ID 15232 Rev 5
13/25