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BQ25176J: BQ25176J

Mohua Duan
Prodigy 10 points
Part Number: BQ25176J

Tool/software:

We using reference design and evaluate this chip, we encounter a few issues:

Battery : 3.2v, 1600mAH, LifePo4 battery, 1 cell;

1) Fully discharge the battery and start to charge the battery using charging current 50mA.

Based on data sheet, the Tsafety is 10hours. After 10 hours, the charging stop. But we observe the charging not stop at 10 hours later. It stop after 19-24 hours (did not when it stopped). 

a) Why it did not stop after 10 hours?

b) the STAT LED blinking, is it correct?

c) It did not stop immediately, the charging current went down 30mA, 20mA then goes to 0mA. It takes a few minutes. Is it correct way?

2) test BAT NTC feature, Vbat is ~3.2V

Put NTC in chamber only, the charging IC in room temperature.

using chamber to heat  increase temperature from 30C-60C, IC stop charging around55C; normal

reduce temperature from 60C-40C in chamber, IC resume charging -> normal;

**

there are 3-4 times, when I take out the NTC from chamber (60C) to leave it in room temperature, the chip did not resume charging.

After these times failure, this symptom can't repeat.

Is there anything we missed? We are quite worry about this. 

3) During 2）test,

we also observed this BQ25176J sometime enters pre-charge status.

We set the charging current 50mA, but the current meter shows the charging current is 20mA or 30mA. The bat voltage is 3.2V.

  • 0
    TI__Guru 70006 points

    Hello

    Mohua Duan said:
    a) Why it did not stop after 10 hours?

    The BQ25176J has TREG feature that will monitor the die temp and reduce output current to limit thermal rise.  When this happens the Tsafety timer will double, increasing from 10hr to 20hr.  This sounds like what you are seeing.

    What is input voltage?

    "b) the STAT LED blinking, is it correct?"

    Yes this sounds correct for a safety timer expire case.

    "c) It did not stop immediately, the charging current went down 30mA, 20mA then goes to 0mA. It takes a few minutes. Is it correct way?"

    This sounds like unit entering CV phase where the current will decrease while voltage is constant. This would be correct

    2.) NTC -- Check the voltage at TS pin during the test.

  • 0 in reply to Bill Johns
    Prodigy 10 points

    1) 

    What is input voltage? => 5V

    When chip in Iprecharge, the I charge is on 20% I set, which is 20%*50mA, 10mA charging current only. And, our heat dissipation plate we designed, it increase to 60C when power dissipation is 0.3W in this chip.

    10mA charging current and Tj will hit 125C and trigger TREG function, we doubt.

    Vset, we set to 3.5V. During our testing, the battery voltage is 3.2V. Because charging current is 50mA only, the voltage increase is not fast. it won't hit 3.5v in short period. 

    Enter CV mode, we also doubt. 

    2) NTC

    It happened only few times only. We can't repeat now. We measured TS voltage, 1.3V, the STAT pin status will change. 

    We worry it happen randomly and will affect our product in the market.

  • 0 in reply to Mohua Duan
    TI__Guru 70006 points

    Hello

    Do you have a schematic of the circuit you can send?

    Couple of things to check:

    1.) what voltage at ISET pin, about 1V for CC mode and 0.2V for pre charge.

    2.) Voltage at TS pin with 10k NTC should be about 380mV, test with 10k Resistor.

    3.) Any current meters or connections in output, they have caused problems before?

    Also the battery is 1600mAh and charge current is 50mA that would be a 32hr charge time.  Is the plan to charge at higher current?