BQ24125: Power management forum

Ye-sheng Kuo

Part Number: BQ24125

Hi,

I designed the charging circuit with BG24125 to charge a 3s1p Lithium-Ion battery. See the schematic below.

However, when I attached a battery (10.8 V), it's not charging.

The voltage at ISET1 --> 0, indicates it's not charging. The voltage at ISET2 --> 0.1 V. The voltage at TS --> 1.5 V. And STAT1 is on (pull to gnd), STAT2 is off (pull to high).

I couldn't figure out what's going on. Any suggestion would be appreciated.

Thanks,

Ye-Sheng

over 5 years ago

0 Jeff F over 5 years ago

TI__Guru*** 143980 points

Hi Ye-Sheng,

With STAT1 being ON and STAT2 being OFF, the charger thinks it is charging, correct? What is your input voltage? What is the voltage measured at TP3?

Regards,

Jeff

0 Ye-sheng Kuo over 5 years ago in reply to Jeff F

Prodigy 240 points

Hi Jeff,

Yes, according to the STAT pins, the charger thinks it's in charging.

The voltage input is 15 V, and the voltage at TP3 is essentially battery voltage divided by resistors. It's around 1.7 V.

Ye-Sheng

0 Jeff F over 5 years ago in reply to Ye-sheng Kuo

TI__Guru*** 143980 points

Ye-Sheng,

What is the voltage at TS pin? I assume PG is low?

Regards,
Jeff

0 Ye-sheng Kuo over 5 years ago in reply to Jeff F

Prodigy 240 points

Hi Jeff,

TS is around 1.5 V. PG is low.

Ye-Sheng

0 Jeff F over 5 years ago in reply to Ye-sheng Kuo

TI__Guru*** 143980 points

Hi Ye-Sheng,

Puzzling. If you remove BAT+ and BAT- bit keep the NTC connected or use a power supply to hold TS pin at 1.5V, do you see the IC go into battery detection with a waveform similar to Figure 11 datasheet page 18?

Regards,
Jeff

0 Ye-sheng Kuo over 5 years ago in reply to Jeff F

Prodigy 240 points

Hi Jeff,

Yes, I didn't connect the NTC, but swapped the resistor to 10k. The battery waveform is similar to datasheet.

Thanks,

Ye-Sheng

0 Jeff F over 5 years ago in reply to Ye-sheng Kuo

TI__Guru*** 143980 points

Hi Ye-Sheng,

Great! If you add more capacitance (>=250uF) instead of replacing battery, does the charger charge the capacitor to your desired voltage?

Regards,
Jeff

0 Ye-sheng Kuo over 5 years ago in reply to Jeff F

Prodigy 240 points

Hi Jeff,

Yes, the capacitor reached the desired voltage.

Ye-Sheng

0 Ye-sheng Kuo over 5 years ago in reply to Ye-sheng Kuo

Prodigy 240 points

Hi Jeff,

I took another board and did some measurement more carefully. What I found were:

1) The voltage across sense resistor is 0.1 V, this indicates 1.5 A flow through the resistor
2) very little current (<10 mA) flow into the battery.
3) Voltage at ISET1 is 1 V, which indicates the charging current is 1.5 A.
4) Voltage at TS is 1.6 V
5) entire system draw 22 mA @ 15 V input

I did test the battery, I can directly charge the battery from power supply without any issue.

From BQ24125 perspective, it thinks it's charging the battery. But somehow the current seems flow back to the BQ24125 pin 14. Is that even possible?

Thanks,

Ye-Sheng

0 Jeff F over 5 years ago in reply to Ye-sheng Kuo

TI__Guru*** 143980 points

Ye-Sheng,

The BAT pin is high impedance. Could there be a solder short? I do not understand how items 5, 1 and 3 correlate. What is the input current and voltage to the charger and what is the output current and voltage?

Regards,
Jeff

0 Ye-sheng Kuo over 5 years ago in reply to Jeff F

Prodigy 240 points

Hi Jeff,

The mystery finally resolved.

The vendor mess up the sense resistor, instead of 0.068 ohm, they put 68 ohm instead. I corrected it and the world is beautiful again :)

Thanks for your help!

Ye-Sheng