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LM74502: Reverse Protection.

Kengo.Y
Guru 11255 points
Part Number: LM74502

Hi team,

I'd like to know about Reverse Protection.

Does this function mean that when EN is enabled and the input voltage is above 3.9V, the FET will turn off if VS is below 2.1V (TYP)?

In other words, even if EN is enabled, if a reverse voltage to VIN from VOUT is detected, the FET will turn off?

And, if EN is connected to VS, is it possible to configure reverse protection with one FET as follows?



Sincerely.
Kengo.

  • 0
    TI__Guru** 105391 points

    Hi Kengo,

    Thanks for reaching out!

    our colleague will get back soon on your questions.

    Best Regards, Rakesh

  • +1
    TI__Expert 3370 points

    Hi Kengo,

    If Vs goes below the POR falling threshold of 2.1V, the GATE pin of the device will be pulled low. But this reverse polarity protection is not the same as blocking reverse current as shown by the red arrow in the drawn diagram. The device only monitors the Vs pin and when it goes below the threshold, turns off the FET; but it does not compare the input voltage with the output voltage to be able to block reverse current as Vin goes below Vout. 

    As for the question of using a single FET with LM74502 as shown, Vin and Vout can connect through the body diode of the FET even if the FET itself is turned OFF. So, say Vs is 2V, then it appears on Vout as 1.3V(2V-700mV), even though the FET is off because Vs is below the POR threshold of 2.1V. Similarly, in the events such as overvoltage, this configuration will not be able to isolate the input from the output. To disconnect the input from the output in such events, two back to back FETs are recommended to be used. 

    Thanks and best regards

    Divyanshu