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TPS546B24A: BP1V5 drops reason

Ann_Lien
Genius 10640 points
Part Number: TPS546B24A

Hello expert,

May I know the reason that BP1V5 drop? Customer has an issue that TPS546B24A will shutdown randomly and they found out AVin/PVin is stable but BP1V5 drops. Per checked with spec, there are 30mA current limit for BP1V5 and I would like to know besides current limit, is there any error will cause BP1V5 drops? Thanks a lot!

Best regards,

Ann Lien

  • 0
    TI__Mastermind 48240 points

     

    BP1V5 operates directly off of AVIN with respect to AGND which is internally connected to DRTN, which should not be connected to any external net other than the bypass return of the BP1V5 capacitor.  The only things what should cause a BP1V5 drop would be:

    1) Loss of AVIN voltage

    2) Disruption of the AVIN to AGND

    3) Loading on BP1V5 

    4) Improper bypassing of BP1V5

    5) Connecting DRTN / return of BP1V5 bypass to anything other than DRTN.

    Do you have a schematic of the affected circuit to share?

  • 0 in reply to Peter James Miller
    TI__Genius 10640 points

    Hello Peter,

    Per checked with customer's board, we tried below steps to debug but there is no further step for it. I sent you email with schematic/waveform/description. please kindly help on it. Thanks!

    1. change decoupling cap(BP1V5 to DRTN) from 1uF to 2.2uF.

    2. add additional 2.2uF from BP1V5 to AGND.

    3. we are hard to measure current from BP1V5 so cannot check if it is overloading.

    4. cannot see anything in Fusion Digital Power Designer GUI since NB cannot communicate with TPS546B24A when this issue happen.

    5. make sure there is no EN pull low root cause.

    6. X-Ray make sure there is no soldering issue.

    7. Already changed external resistor/capacitor like C2390 C2389 R1886 & select model resistor *7. issue is still there.

    Best regards,

    Ann Lien

  • 0 in reply to Ann_Lien
    TI__Genius 10640 points

    comments on item 4 --> cannot see any fault report on monitor page.

  • 0 in reply to Ann_Lien
    TI__Mastermind 48240 points

    Ann,

    VDD5 resetting to 3.9V and AVIN jumping up are both indicating a reset of the internal logic, but it looks like something starts to happen to BP1V5 about 1.5ms earlier.  I don't see anything that should be loading BP1V5 in the schematic.

    It looks like the output voltage discharges in about 200μs, what is the loading condition when this happens?

  • 0 in reply to Peter James Miller
    TI__Genius 10640 points

    Hello Peter,

    I will ask customer for it. Thanks!

    Best regards,

    Ann Lien

  • 0 in reply to Ann_Lien
    TI__Mastermind 48240 points

     

    A couple other questions:

    1) The schematic shows everything connected to a single ground plane, how are they grounds actually connected?

    2) How many boards has the customer built up?

    3) Are all of the boards doing this, or just 1?

    4) Does the BP1V5 return after a period of time?  How long?

    5) Where were the parts purchased?