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LM74700-Q1: Can it be used as a gate controller for high-side switche?

Genius 4935 points

Replies: 12

Views: 190

Part Number: LM74700-Q1

Hi team,

Can you tell me if the LM74700 can be used as a gate controller for a high-side switch?

We are already using LM74700 for reverse connection protection.

Use a high-side switch for another large current line.

Since reverse connection protection has already been made, the only function we want here is to turn the high-side switch gate on and off.

We are thinking that it can be used for gate ON / OFF control.

I think that the following circuit configuration can control the EN pin to turn the switch on and off.

Can the LM74700 be used in this way?

Best regards,

Tomoaki Yoshida

  • Hi,

    It can not be used to drive MOSFET as a high side switch as shown in above picture, because the IC takes power from Anode pin and in this config anode does not get any battery voltage to turn on the MOSFET.

    We recommend LM5060 for high switch driving.

    Regards,

    Kari.

  • In reply to Karikalan Selvaraj:

    Hi Kari-san,
    Thank you for your support.
    In our system, since the load is a battery system, power can be supplied even if the anode and cathode are reversed.
    What about that case?
    In this case, we think that the switch can be switched on and off.
    If available, should the cathode terminal be connected to GND or floating?
    Best regards,
    Tomoaki Yoshida
  • In reply to Tomoaki Yoshida91:

    Hi Kari-san,

    Could you please let me know if you have any updates on this matter?

    We are also considering the LM5060, which is overspec for us.

    I think it is best to use the LM74700 in the expected way.

    So I want to know if it is possible or impossible to use this method.

    Best regards,

    Tomoaki Yoshida

  • In reply to Tomoaki Yoshida91:

    Hi Kari-san,

    I would be grateful if you could let me have your answer concerning this matter.

    I want to start design as soon as possible.

    Best regards,

    Tomoaki Yoshida

  • In reply to Tomoaki Yoshida91:

    Hi

    Let me get back on this early next week, let me know if you require a faster response.

    Regards,
    Kari.

  • In reply to Karikalan Selvaraj:

    Hi Kari-san,

    Thank you for your responce.

    I am waiting for an answer early next week.

    Best regards,

    Tomoaki Yoshida

  • In reply to Tomoaki Yoshida91:

    Hi Kari-san,

    I would be grateful if you could let me have your answer concerning this matter.

    Best regards,

    Tomoaki Yoshida

  • In reply to Tomoaki Yoshida91:

    Hello Tomoaki,

    Assuming you have power on both sides, charge pump will work, turn on may not be a problem.

    But during turn off, LM74700-Q1 shorts anode to gate (anode is usually source, and source to gate is shorted, Vgs =0V).

    Now is MOSFET is oriented as shown by you, during off, drain is short to gate, which means MOSFET will not turn off fully.

    This solution is not possible with LM74700-Q1 , we recommend to use LM5060-Q1 instead.

    Regards,

    Kari.

  • In reply to Karikalan Selvaraj:

    Hi Kari-san,

    Thank you for your support.

    I still don't understand the following explanation.

    "Now is MOSFET is oriented as shown by you, during off, drain is short to gate, which means MOSFET will not turn off fully."

    I draw the following picture.

    I understand that the gate and anode are short-circuited at turn-off, but the MOS source is connected to the anode.

    The drain and gate do not short and Vgs becomes 0V and MOS can be completely turned off.

    Is it my misunderstand?

    Best regards,

    Tomoaki Yoshida

  • In reply to Tomoaki Yoshida91:

    Hi

    In the direction indicated, yes MOSFET will turn on and off also, but cathode can not be connected to GND, as anode - cathode voltage cannot exceed 5V.

    But what i understand is you want to allow reverse current and that is why you connect cathode to GND?

    This can be done in other means as shown in the figure.

    Turn on Q2 to allow reverse current. If Q2 is off, device operates normally (blocks reverse current), but when Q2 is ON, device allows current in reverse direction and forward direction as well.

    .

    Regards,

    Kari.