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BQ27750: Resistance between SCL and GND is abnormal about BQ27750

ke huang
Intellectual 310 points

Part Number: BQ27750

Hi Ti experts,

I met a issue about BQ27750 ,the detail as below：

1；I design a pack with BQ27750, the pack voltage is 4.0V。

2；Measure the Resistance  between SCL PIN  and GND is 150Ω，can not communication with BQ studio，normallly is 250K on PACK。

3； Then I want to Measure the resistance  between SCL PIN and GND by PCM，so I disconnect the cell。

4；But when disconnect  the cell ， Measure the resistance  between SCL PIN and GND on PCM，I found that the resistance become 250K，reconnect cell，can communication with BQ studio。

Could you help to confrim that：

1：why the Resistance  between SCL PIN and GND  become normally，I just disconnect and reconnect the cell。

 2；what will cause the Resistance  between SCL and GND  become to150Ω 

  • 0
    TI__Mastermind 34775 points
    Hi Ke,

    Do you have a schematic of your pack you can share? Does the SCL 150-ohm short to GND occur repeatedly when you connect and disconnect the battery?

    SCL being held low sounds like a clock stretch, but would need to understand your conditions more to figure out why the gauge would clock stretch for so long, if it is indeed a clock stretch. It could be the gauge wasn't powered up/initialized properly.

    How many packs do you see this happen to?
  • 0 in reply to Damian Lewis
    Intellectual 310 points

    Hi damian,

    Thanks

    schematic as below

    The project is MP now. we made 50K PCS, 6PCS have this issue。the Total shipments is 2KK/Y。This issue is urgency。

    This issue find on the pack test station ，we connect the cell to PCM then go to pack test station。 but this issue can nor repeatedlly when I connect and disconnect the battery。

    could you help to confirm what will cause clock stretch?  or can you give me the detail block about scl pin？

    we worry that the packwhen assembly to end equipment  will occur this issue，so that will be a Serious problem。

  • 0 in reply to ke huang
    TI__Guru* 76230 points
    Hi ke
    Clock stretching occurs when the gauge is performing data flash updates. it is not a permanent condition. Why do you have diode D1 in your schematic? What voltage does the pbi pin measure when the device is in this state? if you apply a charge voltage to the device when in this failed state does the device recover?
    thanks
    Onyx