VIPER20BSP datasheet(3/17 Pages) STMICROELECTRONICS

Part #	VIPER20BSP

Description	SMPS PRIMARY I.C.

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

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PINS FUNCTIONAL DESCRIPTION

DRAIN PIN:

Integrated power MOSFET drain pin. It provides

internal bias current during start-up via an

integrated high voltage current source which is

switched off during normal operation. The device

is able to handle an unclamped current during its

normal operation, assuring self protection against

voltage surges, PCB stray inductance, and

allowing a snubberless operation for low output

power.

SOURCE PIN:

Power MOSFET source pin. Primary side circuit

common ground connection.

VDD PIN :

This pin provides two functions :

- It corresponds to the low voltage supply of the

control part of the circuit. If VDD goes below 8V,

the start-up current source is activated and the

output power MOSFET is switched off until the

VDD voltage reaches 11V. During this phase,

the internal current consumption is reduced,

the VDD pin is sourcing a current of about 1mA

and the COMP pin is shorted to ground. After

that, the current source is shut down, and the

device tries to start up by switching again.

- This pin is also connected to the error amplifier,

in order to allow primary as well as secondary

regulation configurations. In case of primary

regulation, an internal 13V trimmed reference

voltage is used to maintain VDD at 13V. For

secondary regulation, a voltage between 8.5V

and 12.5V will be put

on VDD pin by

transformer design, in order to stuck the output

of the transconductance amplifier to the high

state. The COMP pin behaves as a constant

current source, and can easily be connected to

the output of an optocoupler. Note that any

overvoltage due to regulation loop failure is still

detected by the error amplifier through the VDD

voltage, which cannot overpass 13V. The

output voltage will be somewhat higher than

the nominal one, but still under control.

COMP PIN :

This pin provides two functions :

- It is the output of the error transconductance

amplifier, and allows for the connection of a

compensation network to provide the desired

transfer function of the regulation loop. Its

bandwidth can be easily adjusted to the

needed value with usual components value. As

stated

above,

secondary

regulation

configurations are also implemented through

the COMP pin.

- When the COMP voltage is going below 0.5V,

the shut-down of the circuit occurs, with a zero

duty cycle for the power MOSFET. This feature

can be used to switch off the converter, and is

automatically activated by the regulation loop

(whatever is the configuration) to provide a

burst mode operation in case of negligible

output power or open load condition.

OSC PIN :

An RT-CT network must be connected on that pin

to define the switching frequency. Note that

despite the

connection of RT to VDD,no

significant frequency change occurs for VDD

varying from 8V to 15V. It provides also a

synchronisation capability, when connected to an

external frequency source.

ORDERING NUMBERS

PENT AW ATT HV

PowerSO -10

VI Per20B

VIPer20BSP

VIPer20B / VIPer20BSP

3/17

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