BQ25883: Temperature Sensing and Fully charged informing Signal Related Issue

Dear Jayce,

1. The DC voltage is proportional to the thermistor resistance which is proportional to the temperature. The part uses comparators with hysteresis. If the noise is greater than the hysteresis window there could be problems.

2. It says in the datasheet that if the voltage on the TS pin is not between the VT1 and VT5 thresholds that charge is suspended and the charger waits until the temperature is within T1 to T5 to resume charging. I do not know what thermistor or divider you used, but following the datasheet recommendation T1 is 0C. Can you verify the TS voltage when the part stops charging?

Thanks,

Mike Emanuel

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Hi Mike,

1. Actually, seems the voltage of TS pin -- VTS will be sent to the ADC inside the BQ25883. So what's comparators with hysteresis means, means the inside structure of the internal ADC? Since switching noise seems to couple to the TS pin. I want to know, how many times will VTS sampled to give a temperature value. If one time sample one temperature, then the value is possible be affected by switching noise. If many samples and average or something like that to give one temperature result, then the result can be thought not affected by the switching noise on the TS pin. That's what matters now and the point I want to discuss with you.

2. Seems due to low temperature, the volume of the Li-Battery changed and result in a 95% or 98% max charge volume. After charge to 95% around volume, the Li-battery cannot accept charge any more (if charging for several hours, still 95%). Under this situation, BQ25883 will not give the charge complete signal change. Which means that the actual charge complete state in low temperature will not have a charge complete signal to instruct. What's the trigger condition of our charge complete signal, is there any method to achieve a charge complete signal under the described condition?

Thanks.

Best Regards,

Jayce Luo

Dear Jayce,

1. Can you please provide a waveform of the coupling to the switch node?

2. It says in the datasheet that the termination is disabled when a "warm" or "cool" temperature is detected.

Thanks,

Mike Emanuel

Please click "This resolved my issue" button if this post answers your question.

Hi Mike,

1. Waveform as below. Double the switching frequency of boost inside the BQ25883 (switch on and switch off in each cycle, so twice)

So what's the sample way? Single Sample or Multi Sample for a single temperature value out?

I advice to add a capacitor to ground on TS pin, I think can make great improvement, but still want to know the sample and temperature calculate method.

2. What does " the termination is disabled mean"? Once it detect cool and will never self-restart again?

Besides, it is found that the Li-battery can first charge to 95% and then can not charge to 100% using BQ25883 in for example 1°C cool environment. Is such phenomenon generally can be seen in other charger products? If it is the feature of Li - Battery, than how can our mobile phones charge to 100%(at least displayed 100% charged)

Is Li-battery can not be charged to 100% under low temperature a common sense? And how to deal with or overcome this problem. The answer is wanted.

Thanks,

Best regard,

Jayce Luo

Jayce,

Resolving offline.

Thanks,

Mike Emanuel