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CSD17313Q2: The Mosfet is getting quiet hot

SIDDHARTH ROY
Intellectual 500 points
Part Number: CSD17313Q2
Other Parts Discussed in Thread: BQ24170,

Hello,

I am using CSD17313Q2  mosfets in my device for  battery charging circuit which is designed on BQ24170 IC. I have currently 10 PCBs  and out of 10, in 2 PCBs, the Mosfets are getting significantly hot when a current is flowing through them. The current flowing for each boards is about the same(1.2A). The temperature of the PCB near the mosfets is 35-37 degrees in 8 PCBs. But for the 2 which i mentioned above, temperature is is 47-51 degrees.

So I am not sure what could be the possible reason for this.

Is it that the part itself may have some variation from piece to piece?

Or it could be the assembly of the part? (By physically looking , it doesn't seem different compared to other PCBs. But if this could be a suspect, i can get it checked by assembly team using Xray.)

In my current layout design, I have missed to put stitching Vias near the mosfets. But I will put this into my next revision of PCBAs. Will this help if there is peice to piece variation in the mosfet part itself?

Also, is there a possibility that if the mosfets are getting so hot every time I charge my battery, later on there could be any reliability issue? Or the mosfet is still good enough to sustain ?

Kindly provide suggestion/inputs  to handle this scenario.

Thanks,

Siddharth

  • 0
    TI__Mastermind 29535 points

    Hello Siddharth,

    Thanks for your interest in TI FETs. The on resistance of TI FETs is typically a tight distribution around the typical value specified in the datasheet. Furthermore, TI guarantees and tests on resistance of all FETs to be less than the maximum value specified in the datasheet. In your application with 1.2A and TJ = 50C, the dissipation in each FET is only about 50mW which is not much for the 2x2mm SON package. It can dissipate in excess of 2W with a good layout on a multilayer PCB. In any case, a 12C to 15C difference in temperature rise seems high and would indicate around 250mW additional power loss per FET assuming RthetaJA = 50C/W. I don't think part-to-part variation can explain this difference. Can you please verify the operating conditions: VGS drive voltage, MOSFET current by measuring the voltage drop across the sense resistor, input voltage, battery charging current and battery voltage? How are you measuring the FET temperatures? With an IR camera? Reliability should not be an issue if you keep the junction temperature less than TJmax with some margin (15C - 25C). Let me know what you find.

    Thanks,

    John Wallace

    TI FET Applications

  • 0 in reply to John Wallace1
    Intellectual 500 points

    Hello John,

    Thanks for your valuable inputs. I checked the boards again and in the 2 boards where the Mosfets are heating up has a short between Source and the drain. The impedance is 40 and 60ohms respectively on those 2 boards where as ideally it shall be 499K as I have resistor between source and drain of that value. Other boards I can see 499K. So I think either the Mosfet pads are internally short during assembly or the capacitor /resistor across the Source and drain is faulty. I have sent it for inspection to my assembly team.  They will check and replace the part and once new part the assembled, will check the impedance again just to cross check between the source and the drain.

    Thanks once again.

    regards,

    Siddharth

  • 0 in reply to SIDDHARTH ROY
    TI__Mastermind 29535 points

    Hello Siddharth,

    Thank you for the update and please let me know if I can be of further assistance.

    Regards,

    John