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TPS56637: Can the customer apply 3.3V external power to the buck converter output trace if Vin is open?

Ikoma
Intellectual 940 points
Part Number: TPS56637

Hi Expert,

The customer uses TPS56637 to configure a 3.3V Vout buck converter on their application board. So, normally they uses this converter to supply 3.3V power on their application circuit. However, there is a case that they want to apply 3.3V power by external source for test purpose. In this case, can the customer apply 3.3V external power to the output trace of TPS56637 buck converter?
In other words, can the customer apply 3.3V to SW node trace in case that there is no voltage applying on Vin and EN pin?

I think if Vin is not open and a current path can be assumed from Vout to Vin via body diode of high side FET, it can't be allowed. But if Vin is open, it maybe OK. Do you have any other concern about this use case?

Thanks for your help in advance.

Regards,

  • 0
    TI__Genius 9550 points
    hi,
    It is ok @ (vin open) & (Vout 3.3V from another power supply).
    Please connect Milo Zhu via email (peisheng-zhu@ti.com) to get more technical support if you have.
  • Former Member
    0 Former Member
    Hi Ikoma,

    Applying 3.3V voltage to Vout is OK.

    If the high side body diode is on, the Vin pin will be charged to 3.3V - Vd (0.5V~0.7V), which is lower than the UVLO threshold of Vin. TPS56637 won't work then. Vd is the forward voltage of body diode.

    There is a risk only when apply 4V+Vd to Vout and set TPS56637 as FCCM mode. At this condition, Vin will be higher than UVLO threshold of Vin, TPS56637 can work as a boost converter when it is set as FCCM mode.

    I recommend to use EN resistor divider to set a higher UVLO value in case TPS56637 falsely work.
  • 0 in reply to Former Member
    TI__Intellectual 940 points
    Hello Jason, Hello Bruce,

    I see. Thanks for your appropriate answers.

    Regards,
    Ikoma