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LM74670-Q1: Verification of Parallel NFET Configuration, Reverse Current Protection, Spec(s) Affected by Temperature Variation, etc.

Daniel_Foncannon
Prodigy 70 points
Part Number: LM74670-Q1
Other Parts Discussed in Thread: LM74610-Q1

Hi Team,

I have a few questions in regards to the LM74670-Q1. Please see below:

  1. Can the LM74670-Q1 device drive two parallel NFETs?
    1. My thoughts are that the LM74670-Q1 can drive two parallel FETs.

  2. For reverse current protection, would you need two separate LM74670-Q1s and NFETs in a back to back configuration?
    1. My understanding is that the device can't drive two NFETs in series. 

  3. What are the implications of choosing an NFET that has a gate-to-source voltage threshold (VGS(TH)) greater than 3V? Is this related to the body diode conduction mode?

  4. Would I be able to achieve the above applications with the LM74610-Q1? What is the differentiation between the two devices, higher gate drive?

  5. Apart from forward diode voltage spec on the MOSFET, what other specs should be considered across temperature variation?

Regards,

Daniel Foncannon

  • TI__Prodigy 70 points

    Hi Team,

    Any update on this thread?



    Thank you and regards,

    Daniel Foncannon

  • in reply to Daniel_Foncannon
    TI__Expert 5940 points
    Hi Dan,

    1. Yes, the LM74670 can drive parallel FETs. It has higher drive current than the LM74610 (67uA vs 46uA). Keep in mind that you are not driving the FET like in an SMPS application and uA level current is needed to allow a slower transition of the FET turn on vs the body diode conduction to prevent current spikes.
    2. You cannot do back to back FETs and it isn't needed as the LM74670 provides reverse current protection when used per the applications in the DS.
    3. It is recommended that you select FETs in the DS table as they are proven to work. Vgs can be 5.15v when the body diode turns on and you want the FET to be enhanced below 5.15v. Look at the FET Vgs threshold and just as important, the FET plateau voltage to be sure it is low. Higher Vgs threshold and plateau voltages will have problems in operation.
    4. The gate drive is higher with the LM74670 that allows it to turn the FET on a little faster and will allow a higher freq of operation (300 Hz).
    5. Mainly the duty cycle range of the FET vs Body diode conduction of the IC and the FET Rdson temp coeff.

    Brian
  • in reply to Brian Daugherty
    TI__Prodigy 70 points
    Hi Brian,

    Thank you for the detailed response! This answers my question on this thread.

    Regards,

    Daniel Foncannon