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BQ24075 heating issu

Akarsh Dhanpal
Prodigy 50 points
Other Parts Discussed in Thread: BQ24075

hi,

i am working with BQ24075, when i am connecting input supply (5v dc) to pin no. 13 of BQ, my circuit is working fine. when i am connecting battery to BQ 24075, then also is works fine, if there is no USB supply.

But when i connects both battery and external 5v supply, my BQ is getting hot very quickly, i thought it may be because of complete discharged battery. but when i connected a fully charged battery, then also it is gettinh hot.

the circuit i have implemented is attached below.
 i am not using POGGD and CHG pin, and i have connected 10kohm resistor on TS Pin, as i havin only two pin on Li-ion battery.

i havev connected 4.12k on SYSOFF pin, i also connected SYSOFF to ground to other PCB, then also BQ is heating. all other parts and value are same as attached in the circuit.

Please provide me some solution, as i am almost on production stage and facing this issue now. my system required current is 2amp.

Thankyou

  • 0
    TI__Mastermind 19430 points

    How are you connecting the thermal pad?Please make sure it has good connection to the GND plane.  Also please make sure that you power traces are wide enough with good amount of via for heat dissipation. See layout guideline section in the datasheet3 for more detail.

    The application circuit above sets the input current limit to 1.3A and charge current to approximately 800mA. If your system requires a continuous current at 2A, your battery will likely never get charged since the IC will be in battery supplement mode all time. 

    Can you provide your layout as well?

  • 0 in reply to Jing Zou
    Prodigy 50 points

    Dear sir,
    Thanks for your quick reply. I haven't connected thermal pad to ground. Input supply to bq24075 is 1amp. Normal current consumption of circuit is nearly 400mA. In typical cases, it reaches 1.5 to 2amp, once for a second in two minutes. Ground pad is internally connected to ground, so I thought it can't be the problem. But I will go with your advice. Please find below attached the Gerber file. Please have a look on it. And give your valuable comments ASAP.
    Thanking youUPDATE-2-29JAN2016.rar

  • 0 in reply to Jing Zou
    Prodigy 50 points
    Dear sir,
    Thanks for your quick reply. I haven't connected thermal pad to ground. Input supply to bq24075 is 1amp. Normal current consumption of circuit is nearly 400mA. In typical cases, it reaches 1.5 to 2amp, once for a second in two minutes. Ground pad is internally connected to ground, so I thought it can't be the problem. But I will go with your advice. Please find below attached the Gerber file. Please have a look on it. And give your valuable comments ASAP.
    Thanking you
  • 0 in reply to Akarsh Dhanpal
    TI__Mastermind 19430 points

    I do not have the software to open your design files. Please share pdf version or screen capture the layout of the IC. 

    The thermal pad must be connected to the same potential as VSS pin. 

  • 0 in reply to Jing Zou
    Prodigy 50 points

    hi jing,

    thanks for your help. i haven't connected the thermal pad with Vss. as i thought there is an internal connection so not required. i may be wrong. here i am attaching the layout design of my pcb design. please let me know, if any correction is required.

    TOP side

    thankyou

    bottom

  • 0 in reply to Akarsh Dhanpal
    Prodigy 50 points

    hi jing, Please give me some solution for the same, i am in urgent need of it.

    thankyou

    with regards

    Akarsh D

  • 0 in reply to Akarsh Dhanpal
    TI__Mastermind 19430 points

    Akarsh,

    I have already point out in my previous response that the reason is because of the thermal pad connection. As stated in the datasheet, the thermal pad must be connected to VSS. You will have to change the layout to connect the thermal pad.

    For better thermal performance, please also add multiple vias on the bottom of the IC on the pcb. See page 46 example via layout design. Please use our EVM design as reference.