HVLED805

Application information

Doc ID 18077 Rev 1

23/29

5.8

Soft-start and starter block

The soft start feature is automatically implemented by the constant current block, as the

During start-up, as the output voltage is zero, the IC will start in CC mode with no high peak

current operations. In this way the voltage on the output capacitor will increase slowly and

the soft-start feature will be ensured.

on others circuit parameters, like transformer ratio, sense resistor, output capacitors and

load. The user will define the best appropriate value by experiments.

5.9

Hiccup mode OCP

The device is also protected against short circuit of the secondary rectifier, short circuit on

the secondary winding or a hard-saturated flyback transformer. A comparator monitors

exceeds 1 V.

To distinguish an actual malfunction from a disturbance (e.g. induced during ESD tests), the

first time the comparator is tripped the protection circuit enters a “warning state”. If in the

subsequent switching cycle the comparator is not tripped, a temporary disturbance is

assumed and the protection logic will be reset in its idle state; if the comparator will be

tripped again a real malfunction is assumed and the device will be stopped.

This condition is latched as long as the device is supplied. While it is disabled, however, no

decay and cross the UVLO threshold after some time, which clears the latch. The internal

Figure 18.

Load-dependent operating modes: timing diagrams

COMP

65 mV

hyster.

Normal-mode

Burst-mode

Normal-mode