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BQ25756: Mosfets getting damaged

Shahzad Hafeezi
Prodigy 50 points
Part Number: BQ25756

Tool/software:

Hi,

We are trying to use BQ25756 for Solar Street light Application with output power requirement of 250W.

Mostly during programming/ debugging of external controller, mosfets are getting damaged, but its not limited to this, sometimes they got damaged during normal operation.

We have entered in a very critical phase now, its our 3rd attempt to make this product, but we are continuously getting this result.

We have used external supply of 10V for "DRV_SUP". But after having this issue, we reduced output to 7V (by changing Resistor, R2), but still Mosfets are not living up.

Previously (2nd attempt) we used 80V Mosfets "IAUCN08S7N013ATMA1".

This (3rd) time we have used 100V Mosfet "'GT010N10TL".

Attached is the schematic. Mostly M2 or/and M4 are getting damaged.

Input Solar Panel: 500W, 46V.

Battery: 2 x 12V [40AH] in series.

Output (LED): (40V 1.25A) x 2 in parallel. 

We will highly appreciate your quick response.

Thanks,

Muhammad Saad Tariq. 

7612.Schematic PDF.pdf

  • 0
    TI__Mastermind 31305 points

    Hello Muhammad,

    Thanks for being patient with this. We'll take a look at this and get back to you later this week.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    TI__Mastermind 31305 points

    Hello Muhammad,

    Once again, thanks for being patient with this.

    I have a few suggestions/questions for the schematic that may help:

    • Does the circuit behavior improve if you use an inductor with a higher DCR of 10mΩ or so?
    • Can you send me the datasheet for the BTST diodes?
    • When you are using an external gate drive supply, you've disconnected DRV_SUP from REGN right?
    • The schematic you send me doesn't have the component values listed. How much capacitance do you have on VAC and VBAT?

    I have a few setup questions to help debug this:

    • Can you take an oscilloscope capture of SW1, SW2, VBAT, and IBAT? Do these waveforms look normal?
    • Have you managed to capture the FETs breaking on the oscilloscope? This is probably really hard to test. We can probably debug the circuit without this information.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 50 points

    Hello Ethan,

    Thankyou for the support and time. Below are the answers to your suggestions/questions:

    1. First we used inductor "PQ2614BHA-100K" with DCR 1.9 mΩ, then we changed to an inductor with DCR 6 mΩ but the results are same.

    2. Part number of BTST Diodes is "SX3H15-AU_R2_006A1", datasheet attached.

    3. Yes, REGN is not connected to DRV_SUP.

    4. Sorry for sending schematic without values, I'll attach "schematic with values written" shortly. Both VAC and VBAT had 330uF x 2, then we changed it to 100uF x 3.

    For the waveforms, we will try to capture and share them. But to capture FETs breaking will be difficult.

    Best Regards,

    Muhammad Saad Tariq. 

    SX3H15-AU.pdf

  • 0 in reply to Shahzad Hafeezi
    Prodigy 50 points

    Please find attached schematic with values/component part number

    .7612.Schematic with values.pdf

  • 0 in reply to Shahzad Hafeezi
    TI__Mastermind 31305 points

    Hello Shahzad,

    Thanks for the new information.

    For the waveforms, it might just be good to see the circuit working normal operation.

    Also, if possible, can you send me the layout of board?

    Also, do the FETs still break if the 330µF caps are replaced with 50µF or 100µF caps?

    I'll take a more in depth look into your schematic later on this week.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 50 points

    Hello Ethan,

    Can you share some email address so that i can share PCB layout of the board.

    Yes, they were still breaking with lesser capacitance.

  • 0 in reply to Shahzad Hafeezi
    TI__Mastermind 31305 points

    Hello Shahzad,

    Can you send me a private message over E2E of your layout files?

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    TI__Mastermind 31305 points

    Hello Shahzad,

    Thanks for sending me your files over private message. I'm going to mark this E2E thread as resolved for now.

    Best Regards,
    Ethan Galloway