BQ24092: BQ24092 charger can not start fast charging of 1A on almost empty battery

Hi Igor,

Would you be able to share the following information:

• Waveform of voltage at ISET and ISET2 when configured for 1A charging
• Voltage at TS when configured for 1A charging
• Waveform of voltage and current at IN pin when switching from 1A to 100mA and 100mA to 1A?

Hello.

Thanks for your answer.

All the pictures here in the mode of 1A. The battery is completely empty (Standard Ion single-cell 3.7V battery. After discharging below 3.2V it disconnects to 0V).

Following is the voltage on ISET:

The period of this wave is about 18Hz:

Voltage on ISET2 is 0V:

Voltage on TS pin 486mV:

Vin 5V:

Vout 4.17V:

CHG pin high:

What can be the problem that the charger can not wake the battery and start charging?

Interestingly, that even not completely empty battery with a voltage 3.3V i.e. , the charger can not start charging too.

Thanks.

Igor.

Hi Igor,

Hm interesting, is there a chance you could also share the voltage waveform on the battery pin? 

Igor Kagan38 said:

After discharging below 3.2V it disconnects to 0V.

This is interesting. Does this mean that your battery is connected through a protection circuit by any chance?

Thanks for the answer.

Battery pin connected to Vout (see graph in the previous answer).

The battery consists of an over-discharge protection circuit at 3V (in my last answer I wrote 3.2V - it's a mistake. 3V this is the right value).

But as I mentioned before, even in a very weak battery, like 3.3V, the charger behaves as described in the previous post.

Another aspect, that when the battery is about 3.8V, the charging start operating and charge approximately to the current 450mA.

What can be a problem?

Thanks.

Igor.

Igor,

Would you be able to share information about the protection circuit or the battery? Is there a specific reason that the protection circuit is being used outside of over-discharge and is it possible to test without the protection circuit? 

As you say, the protection circuit may be disconnecting the battery from the BQ24092 once it reaches this low voltage and causing the /CHG pin to go high impedance which can indicate no battery detected.

Igor Kagan38 said:

Another aspect, that when the battery is about 3.8V, the charging start operating and charge approximately to the current 450mA.

Considering that this is almost 50% of your programmed fast charge, the device could be reducing the charge current due to seeing the battery at low temperature based on NTC monitoring. This will happen when the TS voltage increases to about 790 mV to indicate low temperature. 

This is standard protection integrated into every Lithium-Ion Battery:

What can be the reason for such strange behavior on ISET (short pulses, like you, can see in the waveform)?

Thanks.

I found some other problems in my schematics. Now everything works properly.

Thanks again.

Igor.