VIPER26 View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

VIPER26

Fixed frequency VIPer™ plus family

STMicroelectronics 

VIPER26

Automatic auto restart after overload or short-circuit

14 Automatic auto restart after overload or short-circuit

The overload protection is implemented in automatic way using the integrated up-down

counter. Every cycle, it is incremented or decremented depending if the current logic detects

the limit condition or not. The limit condition is the peak drain current, IDlim , reported on

Table 8 on page 7 or the one set by the user through the RLIM resistor, as reported in

Figure 13 on page 9.

After the reset of the counter, if the peak drain current is continuously equal to the level IDlim,

the counter will be incremented till the fixed time, tOVL, after that will be disabled the power

MOSFET switch ON. It will be activated again, through the soft start, after the tRESTART time,

see the Figure 26 on page 17 and the mentioned time values on Table 8 on page 7.

In case of overload or short-circuit event, the power MOSFET switching will be stopped after

a time that depends from the counter and that can be as maximum equal to tOVL. The

protection will occur in the same way until the overload condition is removed, see Figure 26

on page 17.

This protection ensures restart attempts of the converter with low repetition rate, so that it

works safely with extremely low power throughput and avoiding the IC overheating in case of

repeated overload events.

If the overload is removed before the protection tripping, the counter will be decremented

cycle by cycle down to zero and the IC will not be stopped.

Figure 26. Timing diagram: OLP sequence

SHORT CIRCUIT

VDD OCCURS HERE

VDDon

VDDCSon

IDRAIN

IDlim_bm

t1*

tRESTART

tOVL

tSS

* The time t1 can be lower or equal to the time tOVL

tRESTART

tOVL

tSS

SHORT CIRCUIT

REMOVED HERE

tRESTART

tSS

time

time

Doc ID 17736 Rev 2

17/25

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