BQ76PL455A-Q1: Top rail getting hot

jarod krane

Part Number: BQ76PL455A-Q1
Other Parts Discussed in Thread: BQ76PL455A

I just made my own BMS using the BQ76PL455A following the eval board for the most part. Upon first testing I noticed that the two 200ohm resistors that are on the top line get really hot, like excessively hot. I was wondering if anyone else has come across this or why this would be happening? Also why is the design recommendation to put two 200ohm in series instead of just one 400ohm? Any answers would be appreciated, thanks.

over 5 years ago

0 Taylor Vogt over 5 years ago

TI__Genius 17370 points

Hi Jarod,

Would you be able to share the schematic so we can understand the changes? Also measuring all of the voltages/current into the top line would be helpful. Having two resistors allows for better thermal dissipation as these can get hot depending on operation mode/current draw.

Regards,

Taylor

0 jarod krane over 5 years ago in reply to Taylor Vogt

Prodigy 90 points

here is the schematic to my board, thanks for the info.

4011.BMS.pdf

0 Roger Hwang over 5 years ago in reply to jarod krane

TI__Genius 10785 points

Hi Jarod,

I don't see why that 200R resistor getting hot.

How many layer is your PCB?

ROger

0 jarod krane over 5 years ago in reply to Roger Hwang

Prodigy 90 points

It is a two layer board. Would it be a problem with my trace thickness going through the top line?

thanks.

0 Roger Hwang over 5 years ago in reply to jarod krane

TI__Genius 10785 points

Hi Jarod,

I am assuming that you only have two single layers.

Good solid ground plane is recommend for thermal and EMI performance.

What about cell balancing resistors?

Check the "W" of the resistor as well.

Check out

You can find layout guide line.

thanks

Roger

0 jarod krane over 5 years ago in reply to Roger Hwang

Prodigy 90 points

Yes it is only two single layers, the bottom is a ground plane although I did have to run some traces through it.

"Check the"W" of the resistors"? are you asking what the power rating of the resistors are? the 200ohm resistors have a 1W rating as well as the 75ohm balancing resistors.

Thanks.

0 Roger Hwang over 5 years ago in reply to jarod krane

TI__Genius 10785 points

Hi Jarod,

1W is way more than enough.

Can you just copy paste resistor section of layout?

Roger

0 jarod krane over 5 years ago in reply to Roger Hwang

Prodigy 90 points

What resistor section of the layout would you like to see? The full schematic is posted above in the thread.

Thanks.

0 Taylor Vogt over 5 years ago in reply to jarod krane

TI__Genius 17370 points

Jarod,

The layout portion looks okay, can you please measure the voltage/current of the rails? Especially to see the top line current on those resistors and if all of the other rails are coming up properly.

Thanks,

Taylor

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BQ76PL455A-Q1: Top rail getting hot