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LMR14050: Backwards leakage from SW to VIN

Gil Winograd
Prodigy 50 points
Part Number: LMR14050

Hi - We are planning to use the LMR14050 to convert between 12V-24V external DC supply on the input side down to 9V on the output side. The output side may also be tied to another power source, e.g. a 12V solar panel.

Can I find out if we provide 12V with an external supply after the inductor connected to the SW pin, what will leak back to the VIN side under the following conditions:

1) EN is forced high, VIN is floating ?

2) EN is connected to to VIN, which is floating ?

3) EN is forced low, VIN is floating ?

Thanks and regards - Gil

  • 0
    TI__Genius 9550 points
    hi Gil,
    Select 3): EN is forced low, VIN is floating.
    This setup, reverse current from Vout (bias 12V) only charge Cin to ~12V, but the device is disable and the device is safe.

    When Vin is lower than Vout, current will flow to VIN via high side mosfet body diode.
    For setup 1) and 2), Vin is higher than UVLO and EN is high, the devive will be enable and switching . This is a wrong operation status.
  • 0 in reply to Jason Wang (BSR-MV)
    Prodigy 50 points
    Hi - Thanks for your feedback.

    For the setup 3), EN is forced low, VIN is floating: You have said that Vin will charge to ~12V, but my question is what will be the reverse current ? If we connect VIN to ground through the ammeter, how much current will flow in reverse from Vout to Vin ?

    For the setup 1 & 2) you have said the device will be switching. But if the Vout is higher than Vin, will the device stop the switching ? In this case, I would think the current should only be the Iq current ?

    Thanks and regards - Gil
  • 0 in reply to Gil Winograd
    TI__Mastermind 33855 points
    Hi,

    In your case, if LMR14050 output is programmed to 9V, and the output is biased with 12V supply, the LMR14050 VIN pin will see 12V and works in standby mode without switching as output is higher than target 9V, this is result for item 1), 2) conditions.

    The chip is shutdown with item 3), so there is also no swithcing.

    If Vin is shorted to ground with small Rs, the reverese current is limited by inductor DCR, highside body diode and Rs.