If VBR > VBR-DIS, the IC starts up and is allowed to switch for 30 msec. After that, if VBR > VBR-OUT (0.4 V, typ.),

it continues switching, otherwise it is disabled. From this latter case, if VBR exceeds VBR-IN (0.5 V, typ.) for more

than TBR_IN (250 usec, typ.), the IC is allowed to resume switching (brown-in); then, if VBR falls below VBR-OUT for

more than TBR_OUT (30 msec, typ.), the IC is disabled (brown-out).

The delay times are implemented through up/down counters, to reject temporary disturbances across the line.

TBR_OUT is also intended to avoid false protection triggerings due to the input capacitor voltage ripple and to

guarantee some hold-up in case of a missing cycle of the input line.

Input OVP, brown-in and brown-out conditions can be set connecting a voltage divider across the rectified input

mains, iOVP, BR and GND and selecting the resistor values according to the equations below.

Equation 10

(10)

ROVP=RHV∙ ViOVP_tℎ

VIN−OVP−VBR−IN

VIN−ON

Equation 11

(11)

RBR=RHV∙ VBR−IN

VIN−ON−VBR−IN

In the above formulas,

VIN_ONandVIN_OVParetheDCinputvoltageswhichtriggerbrown-inandinput

overvoltage protection respectively.

The resistor RHV is used to start up the converter and also as part of the voltage divider, once HV and iOVP

are connecter together. Its value is arbitrarily selected, with the recommendation to be few tens MΩ at least to

minimize the residual consumptions from the input mains.

It is worth noting that the thresholds VIN-ON and VIN-OFF (the input voltage values triggering brown-in and

brown-out respectively) cannot be set independently but are linked to each other. The DC bus voltage value that

turns off the device is thus calculated with the following equation.

Equation 12

(12)

VIN−OFF=VIN−ON∙VBR−OUT

VBR−IN

A 10 nF filter capacitor placed between BR pin and GND is necessary to avoid misbehavior of the brown-out logic

when a high voltage start-up unit is activated.

The brown-in/out function can be disabled connecting the BR to GND.

VIPERGAN50

Brown-In and Brown-Out protection

DS13888 - Rev 2

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