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TPS55287: VCC Supply when both VIN and VOUT < 5V

Paul Barker
Prodigy 235 points
Part Number: TPS55287
Other Parts Discussed in Thread: TPS63810

Tool/software:

I looked through the datasheet but couldn't find recommendations on the VCC supply mode when both VIN and VOUT are below 5V.  For example if VIN=4.5V and VOUT=3.3V then it seems that a 5V supply would have to supplied externally to the VCC pin since the internal LDO would not have enough input voltage to work when connected to either VIN or VOUT.  Just want to verify this since the datasheet does not discuss this case.

Thanks,

Paul

  • 0
    TI__Expert 6750 points

    Hi Paul,

    Thank you for reaching out.  

    1.If external VCC power supply is not used, Vin or Vout directly power VCC at this situation and VCC voltage will be lower than 5V. Converter can work properly when VCC is higher than 3V. If there is some load transient causing input voltage drop or output voltage drop, there is risk that VCC is lower than threshold.

    2.You can use external power supply to power VCC, the recommended value is   between 4.75 and 5.5V.

    3.In this case, what is the output current? We have low Vin buck-boost product TPS63810. Please check if it is suitable here.

    Regards,

    Mulin

  • 0 in reply to Mulin Yuan
    TI__Prodigy 235 points

    The output current is typically 100 mA but sometimes it will be close to 3 Amps.  I will probably just use the USB +5V on my board to power the VCC pin so I don't need to be concerned with VIN or VOUT becoming too low.  Thanks.  

  • 0 in reply to Paul Barker
    TI__Expert 6750 points

    Hi Paul,

    It is okay. I will close this thread. If you have more question, feel free to reply and it will open again.

    Regards,

    Mulin