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BQ24600: bq24600 Application

Jerry West
Intellectual 350 points

Part Number: BQ24600

I am currently puzzled with the performance of my board. I am charging 4 series 5AH LiPo cells. I have set the bq24600 to charge at 1 Amp. The charger comes up and charges at 1 A for about 1 minute, then it goes to zero for about 30 seconds, then repeats this sequence until the charge is achieved. My first thought was temperature shutdown, but the chip is not warm. I have attached my schematic. If you have any ideas, I would appreciate hearing them.

Jerry WestDEH-8117-001 RB SCH.pdf

  • 0
    TI__Mastermind 43175 points

    Dear Jerry,

    1. Can you please capture waveforms of VCC, PH, the charging current, and SRN?

    2. Can you please probe the STAT, /PG, STAT, and SRN?

    3. How long is the cable connecting the battery to the charger? In other words, during charging, is there a significant difference between the terminal voltage of the batteries and the charger? This could cause early termination.

    4. Why is the VFB pin tied to the charge enable? VFB should be tied to the battery.

    Thanks,

    Mike Emanuel

    Please click "This resolved my issue" button if this post answers your question.

  • 0 in reply to Michael Emanuel35
    Intellectual 350 points

    Hi Mike,

    My technician did not get the chip with the cool mist, I tried it myself by removing the board from the assembly and running the charger so that i could see the chip. If I hit the chip with a little cool mist every 15 seconds, it will work without failure. Do you see any design errors in the schematic that might result in the chip over heating? The board is small but has an inner ground layer that is thermally connected to the thermal pad of the chip with four vias with 8 mill plated holes. the inner layer ground plane is 3.5 x 2.5 inches. i did not expect heat problems at this low current.

    Thoughts please?

    Jerry  

  • 0 in reply to Jerry West
    TI__Mastermind 43175 points

    Jerry,

    In the first post you observed that temperature does not seem to be an issue. If you could collect the information requested from my last post, that would greatly assist me in finding the problem.

    In addition, I would like you to probe the TS voltage, charge current, battery voltage, and input current during this problem.

    Without this information it is hard for me to make a conclusion.

    Thanks,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    Intellectual 350 points

    Hi,

    I have obtained most data requested. The Stat and /PG are not connected in my board and thus are not exposed for probing.The scope pictures are synchronized to the charge current waveform. The design current is 1 Amp.

    CHANNEL 1 IS SRN  -  CHANNEL 2 IS CHARGE CURRENT

    CHANNEL 1 IS VCC - CHANNEL 2 IS CHARGE CURRENT

    CHANNEL 1 IS PH - CHANNEL 2 IS CHARGE CURRENT

    SAME AS ABOVE W/O TIME BASE EXPANSION

    Jerry

  • 0 in reply to Jerry West
    TI__Mastermind 43175 points

    Dear Jerry,

    Is there any way you could capture the STAT and /PG pins? They are very useful for debugging the status of the charger.

    In addition, can you please detail what thermistor is connected? In addition, what does the TS voltage look like alongside the charge current? I am wondering if it is a temperature issue, but on the battery not the charger.

    Thanks,

    Mike Emanuel

    Please click "This resolved my issue" button if this post answers your question.