Operation description

VIPER37

24/35

Doc ID 022218 Rev 1

8.8

Overvoltage protection (OVP)

The device can monitor the converter output voltage. This operation is done by the CONT

pin during Power MOSFET OFF-time, when the voltage generated by the auxiliary winding

tracks the converter's output voltage, through turn ratio

(see

Figure 28).

In order to perform the output voltage monitor, the CONT pin must be connected to the aux.

four consecutive times, the controller recognizes an overvoltage condition. This special

feature uses an internal counter; that is to reduce sensitivity to noise and prevent the latch

from being erroneously activated (see

Figure 28). The counter is reset every time the OVP

signal is not triggered in one oscillator cycle.

Referring to

Equation 2

Equation 3

where:

●

●

●

●

●

●

●

calculated by:

Equation 4

N

AUX

N

SEC

--------------

k

OVP

V

OVP

N

AUX

N

SEC

--------------

V

OUTOVP

V

DSEC

+

() V

DAUX

–

⋅

-----------------------------------------------------------------------------------------------------

=

k

OVP

R

LIM

R

LIM

R

OVP

+

----------------------------------

=

R

OVP

R

LIM

1k

OVP

–

k

OVP

-----------------------

×

=