BQ24725A: ACFET damaged during cold start

Naveen Kumar

Part Number: BQ24725A

Hi,

When I do a cold start and the system output is connected to a 6A load, my ACFET gets damaged. The battery was disconnected during this test, and the input to the battery charging IC is an 18-volt DC.

Please clarify whether it is recommended to do a cold start. Also, ACDRV is dropped to 16V.

I'm using NTMFS4C029NT1G for the ACFET and RBFET.

8 months ago

0 Aya Khedr 8 months ago

TI__Genius 16622 points

Hi Naveen,

Thank you for reaching out!

Could you please provide your schematics?

I will look into this and get back to you by Wednesday.

Best Regards,

Aya Khedr

0 Naveen Kumar 8 months ago in reply to Aya Khedr

Prodigy 20 points

Hi Aya Khedr,

Here is the schematic FYR.

0 Aya Khedr 8 months ago in reply to Naveen Kumar

TI__Genius 16622 points

Hi Naveen,

Thank you for providing the schematics.

I will review and get back to you by Friday.

Best Regards,

Aya Khedr

0 Aya Khedr 8 months ago in reply to Aya Khedr

TI__Genius 16622 points

Hi Naveen,

Just to clarify, is the 18V adapter plugged in when this behavior is observed?

Also, I noticed that pin 11, BATDRV, seems to be floating in your design. Is it meant to be connected to R306?

Best Regards,

Aya Khedr

0 Naveen Kumar 8 months ago in reply to Aya Khedr

Prodigy 20 points

Hi Aya Khedr,Yes, the adapter is connected, and the system load of 6A is also connected. Regarding the BATDRV, we have used a P-Ch Mosfet to connect the battery to the system. Once the adapter is unplugged, through Q23, the battery voltage will be connected to the system.

Q21 Mosfet is completely shorted, and Q25 Drain-Source is getting shorted. Rest all other FETs are healthy.

0 Aya Khedr 8 months ago in reply to Naveen Kumar

TI__Genius 16622 points

Hi Naveen,

Our battery charge controllers are typically expecting a battery to be present. Is there a particular use-case in your design where the battery is disconnected?

In regards to BATDRV, I highly recommend following the typical application/EVM schematics (N-channel MOSFETs). I also recommend looking into section 9.2.1.2.8 Input Filter Design in the datasheet.

Please let me know if you have additional questions/concerns.

Best Regards,

Aya Khedr

0 Naveen Kumar 8 months ago in reply to Aya Khedr

Prodigy 20 points

Thank you Aya Khedr, after adding the damping network it works fine now!!

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BQ24725A: ACFET damaged during cold start