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LM5164: Questions on Operation

Part Number: LM5164

Hi Team,

My customer has brought up a couple question on the LM5164 that I'd like to get your help with:

  1. How will the LM5164 behave if we were to feed in a VIN that is equal to the setpoint for VOUT? This might exist for short periods of time in some use cases.
  2. Is it okay to provide a voltage on the SW pin if the VIN and EN pins are high impedance?

Thanks,
Mitchell

  • Mitchell,

    1. If your VIN falls too low then VOUT will follow it in drop-out mode, the ON-time will stay the same but the OFF-time will reduce to minimum off-time and duty cycle D will increase to its maximum.

    The total amount of voltage drop depends on the maximum duty cycle, the output current, and the inductor and FETs resistances. See related appnote: Understanding output voltage limitations of DC/DC buck converters or slyt293

    2. There is a parasitic diode in the HS MOSFET, when you apply external voltage to SW pin higher than VIN pin the MOSFET diode can conduct. Even if it is high Z, you should still consider CIN would sink current to charge up to SW-diode voltage. You risk damaging the device with this.

    Let me know if you have further questions,

    -Orlando