L6591 datasheet(18/32 Pages) STMICROELECTRONICS

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Application information

L6591

18/32

Figure 11.

Hiccup-mode OCP: timing diagram (device self-supplied)

5.5

Latched shutdown

The L6591 is equipped with a comparator having the non-inverting input externally available

at the pin DIS (#2) and with the inverting input internally referenced to 4.5 V. As the voltage

on the pin exceeds the internal threshold, the IC is immediately shut down and its

consumption reduced at a low value.

The information is latched and it is necessary to let the voltage on the Vcc pin go below the

UVLO threshold to reset the latch and restart the IC. To keep the latch supplied as long as

the converter is connected to the input source, the HV generator is activated periodically so

that Vcc oscillates between the start-up threshold VccON and VccON – 1 V. It is then

necessary to disconnect the converter from the input source to restart the IC. This operation

is shown in the timing diagram of Figure 12. Activating the HV generator in this way cuts its

power dissipation approximately by three (as compared to the case of continuous

conduction) and keeps peak silicon temperature close to the average value.

Vc c

LVG, HV G

OC P latch

Sec ondary diode is s horted here

Vcc_ OK

1.5 V

PFC _S top

Vcc

Vccoff

Vcc

resta rt

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