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LM74700-Q1: Using as a load switch

karthik raja1
Prodigy 30 points
Part Number: LM74700-Q1
Other Parts Discussed in Thread: LM5060,

Dear Team,  

Can we use LM74700 as load switch?

While using as per the above circuit the output voltage is always on even the enable pin is set to low 0V.

The Output is not turned OFF...

  • 0
    TI__Genius 16305 points

    Hello Karthik Raja,

    LM74700 can not be used  as a load switch, because when EN is pulled low, gate is turned off by connecting gate pin of IC to anode pin of IC.

    When used as an ideal diode, shorting gate to anode is same as Vgs =0V for MOSFET and MOSFET turns off.

    However, in case of using as load switch MOSFET orientation is changed and source-drain position are swapped. This means with EN pulled low, gate to drain = 0V but Vgs is not 0V, So the MOSFET acts as a voltage follower and power is present on the output.

    Regards,

    Kari.

  • 0 in reply to Karikalan Selvaraj
    TI__Genius 16305 points

    Hello Karthik,

    LM5060 is a good option to use MOSFET as a load switch.

    Regards

    Kari.

  • 0 in reply to Karikalan Selvaraj
    Prodigy 80 points

    This is not clear from the data sheet at all.

    What is the purpose of the enable pin? Is it to save power for the gate driver or does it disable some other logic?

    In fact looking at the circuit the body diode of the mosfet will conduct and supply power to the load even if the Vgs = 0.  

  • 0 in reply to Denis Dowling
    TI__Genius 16305 points

    Hello Denis,

    Please note that LM74700-Q1 is mainly an Ideal Diode controller and when EN is low the MOSFET is off, its body diode blocks the reverse current flowing back into the input/battery side.

    EN pin helps to turn of the MOSFET and enter a low Iq shutdown mode (device takes <1.5uA currrent).

    Body diode of the MOSFET conducts to provide power to low power MCUs such as CAN/LIN or the maintenance tasks.

    EN is controlled based on the system requirements.

    Regards,

    Kari.