VIPER31 datasheet(24/40 Pages) STMICROELECTRONICS

24 / 40 page

Figure 35. Connection for input and output overvoltage protections (iso/non-iso topologies)

GND

DRAIN

GND

VCC

UVP

COMP

CONTROL

VIPER31

CIN

DIN

~ AC

OVP

from VAUX or VOUT

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)

RL=Vin_UVP+IUVP_pull−up·RH− Vin_UVP+IUVP_pull−up·RH2−4·VUVPtℎ·IUVP_pull−up·RH

2·IUVP_pull−up

and Equation 8.a) for RM:

Equation 10

VIPER31

Undervoltage and overvoltage protection

DS13285 - Rev 3

page 24/40

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