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Original question:

LM74502: MOSFET usage

LM74502: reverse battery protection with VS and SRC connected

Clement Magnien
Prodigy 90 points
Part Number: LM74502
Other Parts Discussed in Thread: LM74500-Q1

Hello,

My question was already asked on this forum but I would like to confirm. I would like to use this chip in reverse battery protection mode ( don't need back to back MOSFETs to create a real switch).

SRC will be connected to VS, I am not sure SRC pin  is designed  for the reverse voltage as VS?

Regards,

Clement

  • +1
    TI__Guru 57737 points

    Hi Clement,

    Even with the presence of load switch FET when the input is subjected to input reverse polarity, the body diode of the Load switch FET will be forward biased and the SRC pin will just be a diode voltage drop greater than input voltage.

    The SRC pin can handle negative voltage as much as VS pin voltage. So, you can use the device to drive just the Ideal diode FET. 

    In this case, I would recommend you to use LM74500-Q1 which can drive only the Ideal Diode FET and can protect from input reverse polarity. 

  • 0 in reply to Praveen GD
    Prodigy 90 points

    Hi,

    Thanks, yes but SRC is protected by the MOSFET on the right again any current going back to the pin SRC ( not the case when SRC is connected to VS) but I will use the LM74500.

    For the LM74500, if EN is going from a MCU for example, I am concerned if a negative voltage is applied in input, maybe the negative voltage can pass through EN pin and break the circuit behind? Maybe there is a need of a diode in series between the MCU and EN pin?

    Regards,

    Clement

  • +1 in reply to Clement Magnien
    TI__Guru 57737 points

    Hi Clement,

    Yes, using a diode in between the MCU and EN pin of LM74500-Q1, you can make sure the negative voltage on EN pin is not reflected on the MCU.