Datasheet

DocID023409 Rev 5 25/34

HVLED815PF Device description

Figure 20. Load-dependent operating modes: timing diagrams

4.9 Soft-start and starter block

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

primary peak current will be limited from the voltage on the C

LED

capacitor.

During the startup, as the output voltage is zero, the IC will start in constant current (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.

Actually the C

LED

value is not important to define the soft-start time, as its duration depends

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

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

4.10 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. An internal comparator

monitors continuously the voltage on CS pin and activates a protection circuitry if this

voltage exceeds an internally fixed threshold V

CSdis

(1 V typ. - see Table 5: Electrical

characteristics on page 9).

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

energy is coming from the self-supply circuit; hence the voltage on the V

capacitor will

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

start-up generator is still off, then the VCC voltage still needs to go below its restart voltage

before the V

capacitor is charged again and the device restarted.

AM13570v1

COMPL

COMP

50 mV hysteresis (Hys)

Burst-mode

Normal-mode