VIPER37

Operation description

Doc ID 022218 Rev 1

19/35

8

Operation description

The device is a high-performance low-voltage PWM controller chip with an 800 V avalanche

rugged power section.

The controller includes: the oscillator with jittering feature, the startup circuits with soft-start

feature, the PWM logic, the current limit circuit with adjustable set point, the second

overcurrent circuit, the burst mode management, the brownout circuit, the UVLO circuit, the

auto-restart circuit, and the thermal protection circuit.

The current limit set-point is set by the CONT pin. The burst mode operation guarantees

high performance in standby mode and helps to accomplish the energy saving norm.

All the fault protections are built in auto-restart mode with very low repetition rate to prevent

the IC overheating.

8.1

Power section and gate driver

The power section is implemented with an avalanche ruggedness N-channel MOSFET,

which guarantees safe operation within the specified energy rating as well as high dv/dt

at 25

° C.

The integrated SenseFET structure allows a virtually loss-less current sensing.

The gate driver is designed to supply a controlled gate current during both turn-on and turn-

off in order to minimize common mode EMI. Under UVLO conditions an internal pull-down

circuit holds the gate low in order to ensure that the power section cannot be turned on

accidentally.

8.2

High voltage startup generator

The HV current generator is supplied through the DRAIN pin and is enabled only if the input

current is reduced to 0.6 mA, in order to have a slow duty cycle during the restart phase.