Figure 37. Connection for input and output overvoltage protections (iso/non-iso topologies)

C1

Cs

GND

DRAIN

GND

VCC

UVP

COMP

CONTROL

FB

VIPER31

CIN

RH

DIN

RL

~ AC

OVP

RM

from VAUX or VOUT

C2

R2

The voltage divider equations are:

Equation 7

(7)

Vin_UVP= VUVPtℎRL−IUVP_pull−up · RH+RM+RL +RL·IUVP_pull−up

Equation 8

(8)

Vin_OVP= VOVPtℎ− RH

RH+RM+RL· RL·IUVP_pull−up ·RH+RM+RL

RM+RL

Considering that the value of RH is much higher than the values of RM and RL (Mohms vs. kohms), equations 7

and 8 can be approximated into Eq. 7.a) and Eq. 8.a) respectively:

Equation 7.a

(7.a)

Vin_UVP    VUVPtℎRL−IUVP_pull−up ·RH+RL·IUVP_pull−up

Equation 8.a

(8.a)

Vin_OVP   VOVPtℎ−RL·IUVP_pull−up · RHRM+RL

Selecting arbitrarily the RH value, Equation 7.a) can be solved for RL:

Equation 9

(9)

VIPER31

General description

DS13285 - Rev 6

page 24/39