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LM5163-Q1: SW pin in high impedance for LM5163-Q1?

Antonio Faggio
Expert 8050 points
Part Number: LM5163-Q1


Hi,

Is the switching pin of the LM5163-Q1 (SW) in high impedance for disabled power supply? (EN < 1.1V)

Thank you,

Antonio

  • 0
    TI__Guru* 78725 points

    Hi Antonio,

    Thank you for posting!   I believe it will be high impedance when disabled.  However, in a real circuit the power inductor still offers a path to Vout. 

    If you want the SW to be high impedance right away when pulling EN low, it may not be the case because the internal VDD may still hold the voltage to enable the low side FET.  The FET will be turn off after the VDD decays, so there will be some delay time which is not given in the datasheet.  

    Thanks,

    Youhao

  • 0 in reply to Youhao Xi
    TI__Expert 8050 points

    Thank you

    Therefore, if EN of the LM516x is always kept low (or if an unspecified delay is expected),
    there shouldn't be any problems feeding Vout from another regulator/power supply (SW is in high impedance).

    Thanks again,

    Antonio

  • 0 in reply to Antonio Faggio
    TI__Guru* 78725 points

    Hi Antonio,

    Let me double check with our designer (ooo currently) to be 100% sure that there is no weak pulldown implemented when the device is OFF.  

    By the way, feeding Vout higher than the VIN will be a problem.  Note that the high side FET has a body diode :-)

    Will update next week.

    Best Regards

    Youhao

  • 0 in reply to Youhao Xi
    TI__Guru* 78725 points

    Hi Antonio,

    Sorry for the delay.  I got the confirmation from our design team that the SW pin will be in high impedance when EN is <1.1V.

    Please do not forget the other conditions that we already discussed:  residual VCC voltage may keep the low side FET on before it decays; and the high body diode can provide a low impedance path to VIN. 

    Thanks,

    Youhao