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BQ29209: BQ29209 issue

li darren
Intellectual 520 points
Part Number: BQ29209
Hi,
I manufactured  and desigened battery package in BQ29209.
In the production process, found 3 pcs BQ29029 was broke down.
No matter what the battery voltage(Cell2 or Cell1) is high, the pin 3(VC1_CB) always output 0.2V, then Q2 is breakover, cell1 discharge by RCB_EXT. Cross the BQ29209 on the issue board and the normal board, the fault following issue chip. So I judged the chip pin 3 was damaged.
Could you help me, What is the failure reasons of the chip? Are there any hidden peril in schematic? 
By the way, the PCBA encapsulated into the battery package after testing, and  battery package placed some days, the issue appeared in the test battery package again.
Attach schematic.
  • 0
    TI__Expert 6085 points
    seems the cells are inducing OV condition. Please check the OUT voltage too. what is the status of the CB_EN ?
    . pin #3 is common for the balance current for CELL#1 and also CELL#2. I have sent you an invite to your email to send the schematics. I will
    be deleting your schematics from the E2E forum post.
  • 0 in reply to Vish Nadarajah
    TI__Expert 6085 points
    Hi Maka and Darren,

    So, if the Cell balancing is NOT ON.

    Then, if pin #3 VC1_CB net is shorted when in circuit (Step 1 & step 2), but the pin and net are OK when the external components
    were removed (Step 3), the issue may be with the external components or some latch up of the Q3/Q4 configuration.

    Did customer check the function of Q4? Seems the FET may fail first with a transient.
    If it were shorted it would pull VC1_CB low and discharge the cell. The reason may be the AO3401A has a
    12V abs max Vgs while the VC1_CB has no spec on our d/s;

    Also did the customer check the full function of VC1_CB after removing the FETs?

    Step 3 result is not completely understood. Seems the pin should be high if cell 2, is high and low if cell 1.


    Let me know,

    Thanks
    vish