BQ24170: BQ24170 The battery is about to fully charge and there is an abnormal

Hi Star,

The BQ24170 regulates the output as sensed at the SRN pin.  At what point on the board were the scope plots measured above?  What is the termination current?  If the termination current is high and the connection to the battery is highly resistive, there could be a 600mV voltage drop = ITERM *R.

Regards,

Jeff

Hi Jeff

Thanks for your reply.

The waveform is measured at the VOUT capacitor, ITERM=200mA..

Waiting for your reply.

Thanks

Star

Hi Star, how is the battery connected? Jeff has previously mentioned if the connection to the battery is highly resistive, then there could be a  600mV voltage drop. 

Hi Jing

Thanks for your reply.

The battery pack is 3s2p, and the internal resistance is not high. After discovering the problem, the customer tested it with a battery comprehensive tester and it was only 136m Ω.

Why is this problem triggered when it is about to be fully charged? The current is very low.

Thanks

Star

Hi Star,

What we are referring is not only the internal impedance of the battery cell but how you connect it to the board. Is it through long wire? How about the connector? 

Also what is the input? Since this is a buck charger, VAVCC – VSRN rising needs to be higher than the sleep threshold.

Hi Jing

Thanks for your reply.

The board connect as below.

The DC power is 19V/1.3A, the input current limit of the board is 1.2A.

Thanks

Star

Hi Star, 

What is the termination current set to? If you continue to charge the battery, does it eventually terminate charge? Or does it keep charging with the behavior in your scope capture?

Here is what we are suspecting. The impedance across the charging path. You can see from your scope capture when the charge current drops, the voltage of the battery also drops quite a bit. V=I*R. The voltage drop/the current difference is the resistance across the SRN pin to the battery cell. The current in your scope capture seems quite low which means something in between has quite large resistance. You can find more details in the link below.

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1220405/faq-bq24105-why-does-the-battery-charger-s-output-voltage-and-current-show-several-pulses-before-charge-termination?tisearch=e2e-sitesearch&keymatch=faq%20BQ24171

Hi Jing

Thanks for your patient answer.

Iterm=Iset*10%=130mA. This phenomenon is probably triggered when the current drops to 500-600mA during constant voltage charging. If this operation (such as POR) is not interrupted, the 24170 will continue to behave like this If you charge the battery slowly, the phenomenon will continue until the battery is not fully charged. Even if the battery is fully charged by other methods, the BQ24170 will be reconnected, and the error will start again one minute.

In addition, the waveform captured from the oscilloscope shows that when the current is 0mA, the voltage drops by 0.6V, and then a negative current of 8-9MA begins to discharge. This process is the same as the battery detection mechanism. Why is triggered Battery detection mechanism?

Waiting for your reply.

Thanks

Star