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TPS650864: Shutdown on UVLO without reason

Vincent DECAUX
Prodigy 30 points
Part Number: TPS650864

Hi, 

We have developped a board with au ZYNQ ZCU7EG powered by a TPS65086470. We've got a µC to control the startup sequence through I²C.

After some difficulties (too much capacitor on converter output), we have finally managed to have power supplies.

Unfortunately, during the ZCU7EG, when the ARM cores are released from reset, the TPS65086470 turn off without any reason, and when reading the status register, it appears to have an UVLO shutdown.

The VSYS is connected to a +12V, and we have checked it, he is perfectly stable, no visible glitch or anything... We have installed a 1µF capacitor closer to the VSYS input to improve stability without any success.

The BUCK converter are supplied with a +5V, here again there is'nt any glitch visible.

All power supplies are stable, and after this shutting down there is no other error flag or anything than UVLO.

What could cause this event?

Thanks in advance

Best regards

Vincent DECAUX

  • 0
    TI__Genius 13216 points

    Hi Vincent,

    Thanks for the question. UVLO is set whenever the supply to the pmic is shut off and will not automatically clear when it is powered again. This means that every time you power up the pmic, UVLO will be high until it is manually cleared.

    Please try manually clearing the UVLO bit during startup before releasing the cores. If the problem continues please check if UVLO gets set again when the pmic shuts off.

    Thanks,

    Daniel W

  • 0 in reply to Daniel W
    Prodigy 30 points

    Hi, yes sorry I've forgot to say that I clear all the flag at startup, The first step of my µC firmware is to read the status flag, then I rewrite all buffer to clear the status flag and set the correct values, then I start the differents buck.

    Unfortunately when ZYNQ starts up, most of the time I lost my power suppliesand the only flag is UVLO.

  • 0 in reply to Vincent DECAUX
    TI__Genius 13216 points

    Vincent,

    Thank you for the clarification. Could you provide a schematic of your design? Additionally, could you provide scope shots of the startups of the bucks?