How to used BQ2057 for 7.4V 4-Cells 4400mAh Li-Ion Battery?

Bhautik Kothadia

Prodigy 90 points

Other Parts Discussed in Thread: BQ2057

Please find above schematic of battery charging IC BQ2057 which we used to charge battery 7.4V 2200mAh Li-ion Battery.

Now we want to charge 7.4V 4400mAh Li-ion Battery with same circuit.

I changed resistor R1 to 0.22 E 1% 1206 in place of 0.68E 1% 1206.

But resistor R1 is heat a lot.

How i can solve this problem?

over 9 years ago

0 Wenjia Liu over 9 years ago

TI__Expert 7730 points

The 0.22 ohm will program the current to 500mA, so do you see the correct current? Also, 7.4V is a non-standard regulation voltage and the circuit should regulate at 8.4V.

Thanks,
Wenjia

0 Bhautik Kothadia over 9 years ago in reply to Wenjia Liu

Prodigy 90 points

Thanks for your reply.

7.4V battery charge upto 8.4V.

We want to charge battery with 440mA.

Any other suggestion regarding why resistor is heat?

0 Wenjia Liu over 9 years ago in reply to Bhautik Kothadia

TI__Expert 7730 points

Were you able to get 440mA to your battery? Can you measure the voltage drop across the Rsns? According to the datasheet, the voltage drop across Rsns is 105mV typical, please let me know if you are seeing that.

Thanks,
Wenjia

0 Bhautik Kothadia over 9 years ago in reply to Wenjia Liu

Prodigy 90 points

Voltage drop across R1 (Rsns) is 120mV.

0 Wenjia Liu over 9 years ago in reply to Bhautik Kothadia

TI__Expert 7730 points

Sorry I took my previous statement back, for bq2057W,the voltage drop over Rsns is 125mV typical so the 120mV that you observed is within the normal range. So the power is around 0.065W which should be ok for most of the 0.22 ohm resistors to handle. Does your resistor have the correct power rating? Besides the heat issue, did you see any other problem? Were you able to achieve the current you programmed?

Thanks,

Wenjia

0 Bhautik Kothadia over 9 years ago in reply to Wenjia Liu

Prodigy 90 points

Yes. rating is right.

Is there any issue?

0 Wenjia Liu over 9 years ago in reply to Bhautik Kothadia

TI__Expert 7730 points

If you are seeing the regulated voltage and regulated current as expected, I didn't see other issues. Did the heat of the resistor cause any further damage to the part? The voltage across the Rsns is normal too and didn't look like it generates abnormal power dissipation. Maybe you can try a resistor with bigger foot print to help heat dissipation.

Thanks,

Wenjia

0 Bhautik Kothadia over 9 years ago in reply to Wenjia Liu

Prodigy 90 points

we used RL1206FR-7W0R22L (0.22 E 1/2W) resistor. Till resistor is heat up.

Please help us to solve this problem?

0 Bhautik Kothadia over 9 years ago in reply to Bhautik Kothadia

Prodigy 90 points

We used 12V supply for battery charging.

Then we try with 9V supply for battery charging, at that time resistor temperature does not rise.

So finally we get solution.

Thanks for your support.

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How to used BQ2057 for 7.4V 4-Cells 4400mAh Li-Ion Battery?