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  • TI Thinks Resolved

TPS65177: abnormal waveforms of SWBK1

Part Number: TPS65177

Hi team,

The waveforms of SWBK1 is really strange, the voltage is about 2V when the switch is off.

Robin

  • Hi Robin,

    I have notified our expert regarding this topic. Please expect a response by 10/12/18.

    Thanks,
    Aaron
  • In reply to Aaron Goodson:

    Hi Aaron,

    This case is really urgent. Please help expedite it.

    I have tested the waveforms of SWBK1 and inductor current today. See below. The test are from different boards with yesterday, so not completely same but very similar.

    I have verified that the diode is not damaged. 

    Yellow line is inductor current and blue line is SWBK1. Hope it is helpful to you.

    Robin

  • In reply to Aaron Goodson:

    In addition, the purple line is VGL waveforms.
    This issue generates a low frequency (about 3kHz) ripple on the VGL.
  • In reply to Robin Yu:

    Hi Robin,

    Is the load on Buck1 changing from very light to moderate/heavy? I am thinking that it may be toggling between PFM/PWM modes. I need to set this up on the bench to see if I can duplicate this switching behavior but it will not be until early next week because right now it is very busy with other support issues.

    Can you tell me the conditions for this: like input voltage to TPS65177, buck1 output voltage, buck 1 load current etc?

    Kind Regards,

    Liaqat

  • In reply to Liaqat Khan:

    Hi Liaqat,

    The Vin=12V, VIO=3.3V. This is for TCON IO, and VIO will power for Vcore=1.8V and SWBK1 is used for VGL1. The load will not vary in a large range.

    I test it with RT6914, it is very stable.

    The most strange thing is that the low level of SWBK1 is about 2V when switch is off. What may make this happen? Any suggestion to dig out the root cause, I could do it from local side at the same time. Customer could not wait for too long time. TPS65177 could be replaced by a lot of Pin2Pin competitors.

    Robin

  • In reply to Robin Yu:

    Robin,
    Thanks for the information. It is indeed very strange that low level is around 2V. The only thing that I can think is some issue with the diode but you said that you have already checked that. Is this issue on many boards or just one/two boards?
    Can you please send me circuit schematics?
    Kind Regards,
    Liaqat
  • In reply to Liaqat Khan:

    Hi Liaqat,

    This is confidential for customer. Please see the schematic in the email I send to you.

    I have test four boards, all of them has the similar issue. But the difference is some of them show this issue in all frame, and others show this issue only at the start of every frame. From the waveforms of VGL. We could see two different waveforms as below, low frequency ripple is genarated. And also the difference varies with boards due to AB-BA test.

    Robin

  • In reply to Robin Yu:

    Robin,
    Since this issue is resolved offline using e-mail communication, I am closing this thread.
    Kind Regards,
    Liaqat

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