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TPS65217: TPS65217C is booting from USB, but not booting from AC.

user5252159
Intellectual 260 points
Part Number: TPS65217

Hei,

I have a board that is based on the Beaglebone Black A5. The board boots fine when I power the PMIC with 5V on the AC input. When I try to power the PMIC with 5V on the USB input (with 5V on AC pin removed), it does not power up. I measured the voltage at the Sys pin when the USB power is applied, see plot below.

HOWEVER: if I first power up the PMIC by applying 5V to the AC pin (which makes the board boot), then apply 5V to the USB pin, and then remove the 5V on the AC pin, the board stays booted, which means that it draws power from the USB pin. This might suggest some issue with in-rush on the USB pin, but I am not sure. 

I have a power supply connected to the VBAT pins, but for these tests this power supply was turned off which means that there is only some capacitance on the VBAT pins.

Any suggestions? Thanks in advance!

regards,

Robert G.

  • 0
    TI__Genius 10885 points
    Hi Robert,

    The USB input has a lower current limit than the AC input. AC defaults to 2.5A while USB defaults to 500mA, and startup appears to be exceeding 500mA.

    This is defined in register 0x01 in the PMIC, where the registers will always reset to their default settings after a power cycle.

    This current limit applies from the input pins to the SYS pin, shown in figure 10 of the datasheet.

    Best Regards,
    Rick S.
  • 0 in reply to Richard Solarski
    Intellectual 260 points
    Hi,

    Thanks for your reply! Is there anyway I can increase the current limit on USB for booting? If not, do you know of any other fix for this issue?

    regards,
    Robert G.
  • 0 in reply to Richard Solarski
    Intellectual 260 points
    Also, why does the PMIC try only once to route USB power to SYS? When I plug in the USB cord the PMIC tries to route USB to SYS, but gives up after appr. 50ms (as shown in the plot), but it never tries to boot up again. Is this behaviour as expected?

    regards,
    Robert G.
  • 0 in reply to user5252159
    TI__Mastermind 30280 points
    Robert,

    There is a 50ms de-glitch when SYS is connected to USB, before DCDCx converters and LDOx regulators start up.

    When the DCDCx converters turn on, this is when you see the voltage drop rapidly. This is a fault due to overcurrent after the de-glitch period ends.

    You say your design is "based on Beagle Bone black". Did you make any changes to the original design that would can a higher than expected inrush current?
    Do you have a schematic you can share?

    It looks like the USB voltage drops pretty far (almost down to 4V). This would be outside the USB spec (4.5V minimum), but should not cause a UVLO fault in the TPS65217 device (~3.3V + 200mV). Therefore, the fault must be due to over-current. Loading down the USB line by increasing the OCP above 500mA would not be a good idea, because then you will have a UVLO problem.
  • 0 in reply to Brian Berner
    Intellectual 260 points

    Hi and thanks for your reply!

    Yes the board is based on the Beagle Bone black, but there is some additional circuitry on the board that draws more current than the BBB. This might trigger the overcurrent.

    Why doesn't the PMIc try to apply USB to SYS more than once? Is there a way to make the PMIC retry? How do I get the PMIC out of the overcurrent trip state? Is power-cycling or push-button the only way?

    regards,

    Robert G.

  • 0 in reply to user5252159
    TI__Mastermind 30280 points
    Robert,

    Another option would be pulling the nRESET pin low and then releasing high.

    This is a separate push-button on the TPS65217CEVM. I believe it is also a push-button on the BBB.

    The TPS65217 will wait 1s after nRESET is released high before trying to re-boot.