AN4116

Functional check

Doc ID 023220 Rev 1

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6

Functional check

6.1

Soft-start

whose typical value is 8.5 msec. This time is divided into 16 time intervals, each

corresponding to a current limitation step progressively increasing. In this way the drain

current is limited during the output voltage increase, therefore reducing the stress on the

secondary diode.

The soft-start phase is shown in

Figure 28 and 29.

6.2

Overload protection

In the case of overload or short-circuit (see

Figure 38), the drain current reaches the IDLIM

value (or the one set by the user through the RLIM resistor). In every cycle where this

(50 msec typical, internally fixed), the overload protection is tripped, the power section is

elapsed, the IC resumes switching and, if the short is still present, the protection occurs

indefinitely in the same way (

Figure 31). This ensures restart attempts of the converter with

low repetition rate, so that it works safely with extremely low power throughput and avoids

the IC overheating in the case of repeated overload events.

Furthermore, every time the protection is tripped, the internal soft startup function is invoked

(

Figure 32), in order to reduce the stress on the secondary diode.

down to zero and the protection is not tripped.

elapse before switching is resumed (

Figure 33).

Figure 28.

Soft-start at startup

Figure 29.

Soft-start at startup (zoom)

AM13094v1

AM13095v1