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TPS65217: SYS is on for 50ms, then goes to 1.2v - repeats infinitly

Troels Folke
Prodigy 50 points
Part Number: TPS65217
Other Parts Discussed in Thread: USB2ANY

Hi,

I've made a board using the TPS65127C and AM3352ZCE.
It is only powered from AC (+5V). USB is connected to GND and the battery pins left floating.
When the board is powered on, SYS goes to +5V for about 50ms, then goes to +1.2V. Then after some time,
this repeats, and does so infinitely.

Below is the voltage waveform for the SYS pin:

Below is the voltage waveform over a 1ohm shunt resistor to the AC pin (beware, capacitance attached to pin):

What can be causing this behavior? What could be causing this behavior?

Best Regards
Troels

  • 0
    TI__Genius 10885 points
    Hi Troels,

    How do you have PWR_EN and PB_IN configured? Figure 20 in the datasheet shows the Global State Diagram, which details how the PMIC will react to various conditions. This may be the most helpful resource for understanding the device.

    SYS is the output of the PPATH, so when PPATH is off if PWR_EN is never asserted, SYS is automatically switched to the BATT pins.

    The reset condition could occur if PB_IN was shorted to GND.

    Best Regards,
    Rick S.
  • 0
    TI__Mastermind 30310 points
    Troels,

    This may sound silly, but I'll similar questions to Rick in a different way and describe the procedure I follow to get some good results and some poor results like what you are seeing.


    Does your board have a physical Push-Button (PB) connected to PB_IN such that when the PB is pressed it shorts PB_IN to GND and that when the PB is released PB_IN is left floating?

    And did you press the Push-Button?

    And how is PWR_EN connected?

    For instance, if I use the TPS65217CEVM without a USB2ANY connection to my PC, then PWR_EN is left floating. If I press the PB, then VBAT & SYS jump up to 4.2/5V respectively and then appear to fall after a few seconds.

    When I connect the USB2ANY from my PC to the board via USB, then PWR_EN is pulled up to 3.3V. Now pressing the Push Button is persistent and VBAT & SYS are high continuously.

    If I HOLD the PB (constantly short PB_IN to GND), as Rick described, the device will go through a Reset condition every ~8 seconds and VBAT & SYS will drop for ~1 second every 8 seconds.

    I hope this helps
  • 0 in reply to Richard Solarski
    Prodigy 50 points

    Hi Richard & Brian,

    Thank you both for taking time to answer.

    And thank you for the hint regarding PB_IN. It was connected to a tactile switch, whose footprint was wrong, thus connecting
    PB_IN directly to GND all the time. This caused the periodic resetting, which I temporarily solved by removing the switch.

    This was not the only problem, however, since the PMIC still kept shutting down ~65ms after starting up (I simulated button press by briefly shorting PB_IN to GND). I thus decided
    to measure all the voltages and signals to/from the PMIC relative to the PPATH output (SYS). From this I found, that LDO4, which is supposed to be 3.3v, only reaches 1v, and 5ms after
    that, the PMIC shuts down (this is consistent with what the datasheet says: PGOOD monitoring is enabled 5ms after strobe). Why does it only reach 1v? I think it could be because I have
    tied LDO4 directly to VDCDC3, as recommended by the schematic checklist in the case one doesn't use DCDC3.

    Here is the measurement of LDO4 (blue) together with SYS (yellow):

    And here is the schematic:

    Best Regards
    Troels

  • 0 in reply to Troels Folke
    TI__Mastermind 30310 points

    Are you referring to this document:

    which says "Tie to voltage higher than output voltage expected" in the "Not Used Features" column for VDCDC3?

    I agree this may be your problem for LDO4. Can you modify your PCB to connect DCDC3 to AC or SYS and re-test? Or is the VDD_3V3A connection between DCDC3 and LDO4 difficult to break?