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LM74700-Q1: use ideal diode controller to drive rectified MOS

Given Ding
Expert 7405 points
Part Number: LM74700-Q1

Hi Team, 

just want to check if ideal diode controller can bee used to drive rectified MOS, for example, to replace the diode in non-syn buck. 

is LM74700-Q1 suitable for this application？ in datasheet, tReverse delay is 0.75us max, so will it limit the Fsw? Thanks. 

 BRs

Given 

  • 0
    TI__Guru 57737 points

    Hi Gven,

    Please have a look at the below e2e FAQ,

    Can an Ideal Diode Controller used as load switch with external MOSFET?

    https://e2e.ti.com/support/power-management/f/power-management-forum/994549/faq-can-an-ideal-diode-controller-used-as-load-switch-with-external-mosfet

    In short, LM74700-Q1 cannot be used to drive the FET in load switch configuration. LM74700-Q1 also is not suitable for switching applications. 

  • 0 in reply to Praveen GD
    TI__Expert 7405 points

    Hi Praveen, 

    I have seen the e2e you shared, but I still have questions. 

    1. in buck application, I can understand that. 

    a. if the controller is used to control Low side NMOS, then Vout is connected to GND, then there will be Vout short protection.

    b. if the controller is used to control High side NMOS, then the body-diode is from Vin to SW, so there is issue

    2. but in boost application, if using N-MOS as rectified MOS, then the body-diode is from SW to Vout, so there should be no concern on if Vout can be blocked. seen below. 

    is there other limitation on using it as switching FET? Thanks. 

    BRs

    Given 

  • +1 in reply to Given Ding
    TI__Guru 57737 points

    Hi Given,

    Your understanding on the Buck and Boost applications is correct.  But you can see below that the peak gate source current of the LM74700-Q1 are in the order of mA's. This means that the controller cannot turn ON the FET faster. Switching controllers generally have gate drive strength in the order of few Amps to ensure fast turn ON of the FET. This is the reason I mentioned earlier that LM74700-Q1 is not designed to operate as a switching controller.