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Original question:

TPS65217: Review of power management design

TPS65217: TPS65217 not powering-on

VSS
Prodigy 160 points
Part Number: TPS65217
Other Parts Discussed in Thread: AM3359,

Brian,

 

I'm currently bringing up a board that uses the AM3359 and the TPS54217D PMIC.

 

Problem: Output of PMIC (SYS) drops off to about +2V and never comes back.

 

About the system: No battery used, PMIC is powered from the AC pin with a +5V generated off a DC-DC converter.

 

I'm aware of the issue with the VIN brown-out condition and have tied a 10K resistor to GND from the BAT and BAT_SENSE.

 

- PWR_EN pin tied high (to +5V)

- PB_IN pin driven high on power-up

 

I see that the SYS output turns on but immidiately shuts down. I also see that all other voltage rails turn-on but shuts off after SYS goes down. Below is a capture of VIN, SYS, PWR_EN & PB_IN pins.

 

 

Below is the screen shot of the schematic

(Please note that INT_LDO & BYPASS have been connected to GND via recommended capacitors on the board).

 

We have trying to get the PMIC up and running for about a week now. Request you to review the design and provide us with inputs to the get the PMIC running.

 

Thanks

Vijay

  • 0
    TI__Mastermind 30310 points

    Please monitor each rail as they begin to power-up:

    1. LDO1
    2. DCDC1
    3. LDO3
    4. LDO2
    5. LDO4
    6. DCDC2 & DCDC3

    It looks like you either have a short on one of your rails or INT_LDO and BYPASS are not connected as well as you think.

    The PWR_EN deglitch is 50ms, and the PGOOD deglitch for each rail is 4ms/2ms (DCDC/LDO), so by my estimate it would be DCDC1 that is not powering on as expected.

    INT_LDO and BYPASS pins are critical to the operation of the device. If you can measure the voltage on these pins, you need to verify that BYPASS = 2.25V and INT_LDO = 2.3V

  • 0 in reply to Brian Berner
    Prodigy 160 points

    Brian,

    Thanks for the response.

    You were right, one of the rails had a short (probably caused by the re-works that I had on the board to correct the missing connections).

    I now have a board that has all the up to date re-works and here is how the VSYS looks like with respect to the two PGOODs.  Earlier the VSYS used to drop to +1V, now it is dropping to to about +4V and tries to combe back after about 50mS (both the PWR_EN and the PB_IN are high all the time).  Does this look like a start-up issue or over current fault? I measure good impedances across all the PMIC output rails.

    Is there a way to confirm the PMIC is out of OFF state and into ACTIVE state before shutting off? Also, I do not see voltages on any of the PMIC DCDC outputs.  I do see voltage output on VLDO1 and LS2_OUT. 

  • 0 in reply to VSS
    TI__Mastermind 30310 points

    Vijay,

    I have identified another mistake in the schematic that could be causing this issue to occur.

    If you refer to the TPS65217x Schematic Checklist, it says:

    • ISET1/2 = Float if not used
    • ISINK1/2 = GND if both are not used

    But your schematic shows these connections backwards (ISET1/2 = GND, ISINK = Float).

    I am not sure if this is the cause of the problem, but there is some evidence that this is a bad idea. If you refer to the ILED equation on page 38 of the TPS65217 datasheet, it shows:

    • ILED = 1048*1.24V/RSET

    With RSET = 0V (GND), you are dividing by 0. Although this may not cause a short (because L4 and FB_WLED and floating, it may cause an issue that is leading to this reset loop you have encountered.