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BQ24610: Q5 and IC explode when battery is connected

user5274120
Prodigy 20 points
Part Number: BQ24610
Other Parts Discussed in Thread: TPS25982, , BQ24618

I have copied the application schematic from the datasheet and added a custom PCB.  I have an intermittent problem where at some point Q5, from the datasheet and the IC will explode when the battery is inserted.  It doesn't happen every time.  I've had these boards for a little over a week now and during that time 3 of 5 have popped.  Since it is only the IC and Q5 that are damaged I assume that means that the chip is turning on LODRV for some reason when it first gets connected and pulling large amounts of current through Q5.  The IC failure only happens when the battery is 1st inserted.  So far, if the failure doesn't happen on battery insert, then the board runs fine. 

Is this a known issue?

Although not in the datasheet, would adding a pull down to LODRV prevent it from turning on when the battery is inserted?

You can see Q5 has internal metal exposed and hole burned through U1.  Schematic attached incase my I'm missing some configuration error compared to the datasheet.

Battery Charger circuit.pdf

  • 0
    TI__Mastermind 29882 points

    Hi, 

    Thank you for reaching out!

    I will review the schematic and get back to you with feedback early next week.

    Best Regards, 

    Aya Khedr 

  • 0 in reply to Aya Khedr
    Prodigy 20 points

    Thank you Aya,  In an attempt to continue testing the board (without destroying any more) I have placed a TPS25982 eval board in between the Batttery and board.  I noticed that when I have the AC power connected and the battery, the BQ24610 is not automatically switching to AC power, but rather running the board off of the battery.  I thought that the IC would favor AC power vs Battery.  Is this the expected behavior or is there a register or something I need to set?

  • 0 in reply to user5274120
    Prodigy 20 points

    Actually I realized that due to the type of FET used to control the battery vs AC connection to the system, the highest voltage source will provide the current.  If I change the FET type (to not have a reverse facing diode) will the IC then control the when the AC/Battery drives the system? 

  • 0
    Prodigy 20 points

    Hello Aya, as I continue testing I notice that there is no current going to the battery even though the STAT LEDs indicate that charging is happening. I've checked all the current set dividers and they all seem to be correct (in my understanding).  Did you notice anything in the schematic that would prevent the battery from charging?

  • 0 in reply to user5274120
    TI__Mastermind 29882 points

    Hi Jimmy, 

    Thank you for your patience and for providing more information. I have a couple questions in regards to the schematic/layout:

    1- I noticed the schematic IC is BQ24618 but here you've mentioned BQ24610 so I just wanted to clarify which device you are using in your design?

    2- Do you have a separate analog ground and power ground? (I can't see that in the schematic but the layout may reflect otherwise)

    3- What is your desired fast charge current? What is the adapter current limit?

    4- Is there a reason why L1 is 4.7uH? See below for typical inductor values based on the charge current. 

    Best Regards, 

    Aya Khedr 

  • 0
    Prodigy 20 points

    Hello Aya,

    1) We are using the BQ24610RGER chip.  Looks like the schematic's visible value didn't get updated with the rest of the chip information.
    2) We are using a single ground plane (well multiple planes, but a single connected ground node) NOT a split plane design.  There is a 1mOhm sense resistor between the battery negative and ground for the fuel gauge.
    3) We can charge up to 6A for a 1S charge rate.  We are charging a 20V 6Ah tool style battery.  Also please ignore the 12-18V input voltage note - it is old and I never updated it.  Currently we are using a 19V wall adapter.  However realizing that the power path as shown in the schematic wont work this way, I will either need to change the PCH FET or change the input voltage to 22V.
    4) L1 (L2 in the schematic) is 4.7uH to achieve a 6A output for charging the battery.

  • 0 in reply to user5274120
    TI__Mastermind 29882 points

    Hi Jimmy, 

    Thank you for the clarification. The typical output capacitance for 6A charge current would be 30uF (your design currently has 20uF).

    Also, the control stage and the power stage should be routed separately. At each layer, the signal ground and the power ground are connected only at the power pad. Please see the layout guidelines for the BQ24610 and let me know if you have any questions/concerns. 

    Layout Guidelines and Example (4) (2).pdf

    Best Regards, 

    Aya Khedr 

  • 0 in reply to Aya Khedr
    Prodigy 20 points

    Hi Aya,

    Thanks for the layout example.  I increased the capacitance to 100uF and added a TVS at the battery connection.  This solved the exploding issue.