SO16N datasheet(31/51 Pages) STMICROELECTRONICS

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L6566BH

Application information

Doc ID 16610 Rev 2

31/51

where

∆fsw and fm (in kHz, with CMOD in nF and RMOD in kΩ) are selected by the user as to

achieve the best compromise between attenuation of peak EMI emissions and clean

converter operation.

5.9

Latched disable function

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

at the pin DIS (8) and with the inverting input internally referenced to 4.5 V. As the voltage

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

consumption reduced to 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 device. 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 startup threshold VCCON and VccON - 0.5 V. Activating the

HV generator in this way cuts its power dissipation approximately by three (as compared to

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

To let the L6566BH restart, it is then necessary to disconnect the converter from the input

source. Pulling pin 16 (AC_OK) below the disable threshold (see

Section 5.12: Brownout

protection) stops the HV generator until Vcc falls below VCCrestart, so that the latch can be

cleared and a quicker restart is allowed as the input source is removed. This operation is

shown in the timing diagram of

Figure 20.

This function is useful in order to implement a latched overtemperature protection very

easily by biasing the pin with a divider from VREF, where the upper resistor is an NTC

physically located close to a heating element like the MOSFET, or the transformer. The DIS

pin is a high impedance input, therefore it is prone to pick-up noise, which may lead to

undesired latch OFF of the device. It is possible to bypass the pin to ground with a small film

capacitor (e.g. 1-10 nF) to prevent any malfunctioning of this kind.

SO16N Datasheet(PDF) 31 Page - STMicroelectronics