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TPS63036 only starts up when i re-apply the Vin quickly a second time

Matt Love
Prodigy 20 points
Other Parts Discussed in Thread: TPS63036

Hello,

Im using the TPS63036 Dc/DC Conv and have a problem when it starts up. 

If i connect VIN of 4.0V the output does NOT go high to the programmed 3V3, the only way to get it to work is to remove the VIN briefly and the re-apply VIN (within say 5 seconds) and then the output VOUT rises to 3V3. 

What would cause this behaviour? this happens on 2  boards i have built.

I have 10uF Cap across VIN about 5mm away from the chip and 30uF (3 x 10uF ceramic X5R) on the VOUT.

The only load i have at the moment is 20mA of an LED to test.

Any suggestions would be appreciated

  • 0
    TI__Expert 8420 points
    Hi,
    I would place the capacitors as close as possible to the device
    What source do you use? As you can see on Fig. 22 of the DS the device requires more current during start up even if your load is only 20mA
    Can you please share some scope plots: Vin Vout , inductor current and input current
  • 0 in reply to Sabrina
    Prodigy 20 points

    Hi,

    Thanks for your reply. Ill get some detail over the weekend but in the mean time. 

    For the source im switching between a bench PSU outputing 3.9VDC capable of 1A, or a 3.8VDC Lipo battery capable of 1.3A.

    The Yellow line shows the Power coming onto the enable pin

    The Blue line is Vout, which should be going to 3V3 but hovers around 0.8V

    Mostly if i remove Vin and re-apply it the blue trace will then go to 3V3, but not always.

    This is the trace on L1 when the error occurs.

    I have no load on the output

    I can see during the error state that there is a ~10mA draw from the PSU.

  • 0 in reply to Matt Love
    TI__Expert 8420 points
    Can you please share your schematic and layout?
    I would also want to check if the device is going in some Undevoltage lockout, therefor I need you to measure the input voltage near the device.
    I would be great If I could get these plots with higher resolution and zoomed in to understand how the device behaves when it shuts down and try to restart again.