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BQ24650: Shunt resistors burning

Randhir Kalsi
Expert 4545 points
Part Number: BQ24650

Hello team,

Please see below customer question:

Our products are currently powered up by a Lead-acid battery, and the charge controller we use is the BQ24650. We used as reference the slva437a document to use this charge controller with lead-acid batteries. However we've had some trouble with our charge controllers, some of the shunt resistors are burning even though they are oversized. Also in some cases we even have to replace the BQ24650 itself and after some minutes it burns again. 

Initially we had a 1/2 watt R17 resistor, but as this started to happen and after we analyzed the circuit we decided to change it to a 2 watt resistor

To find the shorts/hot spots we tried the test with the current limited power supply and battery or resistor in series and ran it on a burned board:

PH pin to ground has 5M ohms to ground.

SRP pin to ground has 5M ohms to ground.

D1OUT has 1M ohm to ground.  

The following image is a thermal image of the burnt board. The measured current in the battery was 20mA and the current in the power supply was 890mA

The IC reached a maximum temperature of 82 degrees Celsius, a thermal image of the same board but with a new IC is shown.

The measured current in the battery was 940mA and the current in the power supply was 890mA  

 We would appreciate your opinion on this matter and any suggestions to solve this issue would be greatly appreciated!

  • 0
    TI__Guru 50741 points

    Randhir,

    Did the board layout follow the BQ25650 "PCB LAYOUT" guidelines on the d/s and refer to the BQ25650 EVM layout? Please note that "the charging current sensing resistor should be placed right next to the inductor output. Route the sense leads connected across the sensing resistor back to the IC in the same layer, close to each other (minimize loop area) and do not route the sense leads through a high-current path (see Figure 25 for Kelvin connection for best current accuracy). Place decoupling capacitor on these traces next to the IC."

    Thanks,

    Ning.

    Please click "This Resolved my issue" button if this post answer your question.