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

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

voltage current generator is turned OFF. The VIPER06 is powered by the energy stored in

In a steady-state condition, if the self-biasing function is used, the high-voltage current

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

Figure 21.

Power-on and power-off

I

DD

V

DD

V

DRAIN

V

DDon

t

tt

t

V

IN

V

DRAIN_START

t

t

Power-on

Power-off

Normal operation

regulation is lost here

V

HV startup is no more activated

With internal self-supply

Without internal self-supply

V

DDCSon

V

DDoff

I

DDch1

I

DDch2