VIPER28 datasheet(20/29 Pages) STMICROELECTRONICS

20 / 29 page

Operation descriptions

VIPER28

20/29

Where:

●

VOVP is the OVP threshold (see Table 8 on page 8)

●

VOUT OVP is the converter output voltage value to activate the OVP set by designer

●

NAUX is the auxiliary winding turns

●

NSEC is the secondary winding turns

●

VDSEC is the secondary diode forward voltage

●

VDAUX is the Auxiliary diode forward voltage

●

ROVP together RLIM make the Output Voltage divider

Than, fixed RLIM, according to the desired IDLIM, the ROVP can be calculating by:

Equation 4

The resistor values will be such that the current sourced and sunk by the CONT pin be

within the rated capability of the internal clamp.

Figure 22. OVP timing diagram

OVP

LIM

OVP

–

OVP

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

VDS

VAUX

STROBE

COUNTER

RESET

COUNTER

STATUS

CONT

(pin 4)

2 µs

0.5 µs

OVP

FAULT

0 →1

1 →2

2 →0

0 →1

1 →2

2 →3

3 →4

NORMAL OPERATION

TEMPORARY DISTURBANCE

FEEDBACK LOOP FAILURE

VDS

STROBE

COUNTER

RESET

COUNTER

STATUS

(pin 4)

2 µs

0.5 µs

OVP

FAULT

0 →1

1 →2

2 →0

0 →1

1 →2

2 →3

3 →4

NORMAL OPERATION

TEMPORARY DISTURBANCE

FEEDBACK LOOP FAILURE

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