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TPS43330-Q1: Buck B Output voltage not getting stablized

Sumit Singh
Prodigy 30 points
Part Number: TPS43330-Q1

Hello Team,

We are using TPS43330-Q1 in one of our designs. The Buck B section is set to 3.5V.
We are observing strange behavior with respect to Buck 2 output. Sometimes output voltage is setting to 3.5V and sometimes the voltage is going to Higher voltage=5.1V.
We have probed the gate waveforms for the high side and low side switching MOSFET  and below is our observation-

1. When output voltage is stable at 3.5V, gate switching waveform is observed

2. When output voltage is not stable and is at 5.1 V, high side gate voltage is continuously high and no switching is observed ,whereas Low Side switch gate voltage is continuously LOW.

Attached is the schematics and captured waveforms. Can you please help us on this.

CH1-Yellow-> Input Voltage (VFF)

CH2-Green-> Buck B output Voltage (P_SOURCE)

CH3-Blue-> High side MOSFET Gate pin

CH4-Pink-> Low Side MOSFET Gate Pin

TPS43330-Q1_schematics.pdf

  • 0
    TI__Mastermind 38550 points

    Hi Sumit,

     Can you please provide us the followings for better understanding the issue?

    1. Is this new design or existing design but the issue just occurs now?
    2. Only one board has the issue?
    3. If not; what's the ratio of the issue?
    4. Can you try to fully follow the reference design from its datasheet? 

    Thanks!

    Phil

  • 0 in reply to Phil Yi40
    Prodigy 30 points

    Hi Phil,

    Below are the answers inline->

    1. Is this new design or existing design but the issue just occurs now?- Its an existing working design.
    2. Only one board has the issue?2 boards
    3. If not; what's the ratio of the issue?
    4. Can you try to fully follow the reference design from its datasheet? 

      We were working on MOSFET replacement due to older MOSFET parts shortage. But suddenly this issue has happened on the board. The Buck 1 output from TPS43330 is correct and stable. Only for Buck 2 we are facing issues. 
      NOTE- We have checked the MOSFET's. All are operational.
  • 0 in reply to Sumit Singh
    TI__Mastermind 38550 points

    Hi Sumit,

      Since it's the first time this kind of issue reported, can you try to replace the 2 TPS43330 devices in case they were damaged during MOSFET replacement? 

      BTW, what's the ratio of the issue? 2 out of the total boards? 

    Thanks!

    Phil

  • 0 in reply to Phil Yi40
    Prodigy 30 points

    Hi Phil,

    We will replace the IC and check as soon as we are having the stocks for them.

    In the meantime, is there anything which we can check on the IC pins and conclude if the IC has been damaged?

    Ratio is 2:2.

    Thanks 

    Sumit

  • 0 in reply to Sumit Singh
    TI__Mastermind 38550 points

    Hi Sumit,

      Can you do following debug?

    1. Figure out the condition to trigger the issue occurring?  
    2. Can you remove the R6152 which is not present in our typical application circuit?
    3. Can you try to power on the PMIC without load at all on Buck B?

    Thanks!

    Phil

  • 0 in reply to Phil Yi40
    Prodigy 30 points

    Hello Phil,

    R6152 is depopulated in design

    Also, when Load is not there I am able to see P_SOURCE=4.1V (regulated and is as expected.
    As soon as I apply external Load, the voltage is dropping to a 2V @0.5A load.

    Can you suggest something on this?

    Thanks and Regards

    Sumit

  • 0 in reply to Sumit Singh
    TI__Expert 7060 points

    Hi Sumit,

    Device expert is based in US timezone and they have public holiday today. Please expect response by tomorrow.

    Br, Jari

  • 0 in reply to Jari Niemela13
    TI__Mastermind 38550 points

    Hi Sumit,

      Do you mean P_SOURCE voltage drops from 4.1V to 2V when 0.5A load external Load applied? and all other rails' loads don't change? If so, what's kind of external load applied? Can you try a pure resistance load? 

      Please also check those components in series completion of soldering. 

    Thanks!

    Phil