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DFAULT; in the "Application ideas" section, another simple circuit is showed to guarantee the same pro-

tection without the SCR.

– Dmon input undervoltage: when an undervoltage on Dmon is detected, MFAULT is put high, Cout is

pulled low (an internal OCP_BOUNCE signal is generated, see fig. 21) and PW_OK falls down. This

function is enabled 64ms after the UVLO signal falls down. Debounce logic is implemented so that

MFAULT and OCP_BOUNCE signals are generated only if the undervoltage condition lasts more than

500µs.

The Dmon UV and OV protections can be set to work with thresholds set for 5V or 3.3V output voltage:

the choice depends on the IC programming.

– Overcurrent protection: the IC provides an on-board overcurrent protection for 5V and 12V main input

pins. Optionally, it is possible to switch the monitoring from 5V to 3.3V output using the IC programming

(see "On board trimming and mode operating" section).

Figure 22. Fault timing diagram

The overcurrent function is implemented with a comparator detecting the voltage drop across an external cur-

rent sense resistor in series with the output. If this voltage gets higher than a fixed threshold (50mV for 5V input

monitoring and 120mV for 12V input monitoring), an internal MAIN_OC signal is generated; a 450

µs debounce

time exists to assert MFAULT high. Depending on the selected operating mode, MFAULT will be latched high

(default latching mode) or pulled low again after about 1s to allow autorecovery (bounce mode).

To disable this function, the input sense pin may be left open (an internal pull-down is provided), shorted to

ground or shorted to 5V or 12V pin.

Mfault

Mfault

POK

POK

Dfault current

Cout

Output

Mfault

POK

Main output’s overvoltage

Output

Mfault

POK

Main output’s undervoltage

Auxiliary output’s overvoltage

Auxiliary output’s undervoltage

(*) Dmon is connected to the Auxiliary output Rail