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Original question:

TPS65220: PMIC Failure to Start

SK-AM62B-P1: TPS6521904 – No BUCK outputs after power-up on custom board

Mallika Vignesh
Prodigy 50 points
Part Number: SK-AM62B-P1


Hello TI Team,

We are facing a power-up issue with TPS6521904 on a custom board and would appreciate your guidance.

PMIC Details

  • PMIC Variant: TPS6521904RHBR

  • Application: Custom SK-AM62B-P1-based board

  • Input Supply: VCC_MAIN = 3.3 V (verified stable at PMIC input)

  • PMIC Configuration:

    • Using factory TPS6521904RHBR variant

    • Power tree designed strictly as per TI SK-AM62B-P1  reference design

Enclosing the snippet of PMIC schematic used in custom board:
image.png

  • 0
    TI__Guru**** 203810 points

    + Name updated

    Hello Mallika Vignesh,

    Thank you for the query.

    Can you probe the output rails and check if they are coming up during power-up

    Please share a searchable PDF version for review.

    Please expect delayed response due to the weekend holidays.

    Regards,

    Sreenivasa

  • 0 in reply to Kallikuppa Sreenivasa
    Prodigy 50 points

    Hi Sreenivasa,

    I have verified the output rails, there is nothing even during power-up.

    Regards,

    Malli

  • 0 in reply to Mallika Vignesh
    TI__Guru**** 203810 points

    Hello Mallika Vignesh,

    Can i assume you used an oscilloscope to measure the outputs?

    If not please connect an oscilloscope and check.

    Regards,

    Sreenivasa

  • 0 in reply to Kallikuppa Sreenivasa
    Prodigy 50 points

    Hello Sreenivasa,

    Yes , I have used oscilloscope connected to rails when powered-up.
    But there is no output.
    I am hereby sharing the schematics of custom board.5621.Optilink_Plus_RevC_sch.pdf

    Regards,
    Mallika

  • 0 in reply to Mallika Vignesh
    Prodigy 50 points

    Hi Sreenivasa,


    We are seeing a repeatable power-up issue that appears to match the datasheet “VSYS slow ramp with FSD enabled” behavior. Sharing scope waveforms.

    Setup:

    • SoC-to-PMIC interface was isolated during this test (to avoid any SoC influence/backfeed)

    • Measurement points:

      • CH1 (Yellow): VSYS (PMIC input supply)

      • CH2 (Purple): BUCK2 output.

    Regards,
    Mallika

  • 0 in reply to Mallika Vignesh
    TI__Guru**** 203810 points

    Hello Mallika, 

    Thank you.

    • SoC-to-PMIC interface was isolated during this test (to avoid any SoC influence/backfeed)

      Please elaborate the circuit that was isolated Did you isolate any of the supply rails?

    Can you probe all the buck outputs

    Can you explain the above waveform?

    I am not sure on the reason for the input voltage to fluctuate. Can you confirm the input voltage is stable?

    Regards,

    Sreenivasa

  • 0 in reply to Kallikuppa Sreenivasa
    Prodigy 50 points

    Hi Sreenivasa,

    PMIC outputs fully isolated from SoC and peripherals.
    PMIC powered only from its 3.3v stable input
    Here are the waveforms for all the buck outputs.

    • CH1 (Yellow): VSYS (PMIC input supply)

    • CH2 (Purple): BUCK1 output.

    • CH1 (Yellow): VSYS (PMIC input supply)

    • CH2 (Purple): BUCK2 output.

    • CH1 (Yellow): VSYS (PMIC input supply)

    • CH2 (Purple): BUCK3 output.

    • I am sharing the logic analyzer output where channel 2 is supply voltage and all other channels are output rails.


    • Note:


      • In the TI schematic, a pull-up resistor R618 (10k to VCC_3V3_MAIN) is shown on the PMIC_PBn net.

      • However, on the physical TI SK-AM62B-P1 EVM board, R618 appears to be not populated (DNP), yet PMIC_PBn still reads ~3.3V and the PMIC sequences normally.

      On our custom board, we followed the schematic and populated R618 = 10k. Is R618 intended to be populated on custom designs, or should it be DNP like on the EVM?


      Regards,
      Malli