BQ27Z561-R1: two battery in parallel issue

Stone Zeng

Part Number: BQ27Z561-R1

Hi Team,

my customer use two battery in parallel in fold screen smartphone, each battery has one BQ27Z561-R1 inside, battery A is 1210mAh, battery B is 2750mAh. The charging current is ~9A. when stop charging, smartphone is at standby mode and consume a few mA current, battery A charge Battery B with ~140mA current. 25 minutes later, two batteries are balanced which means no charging current, the remain capacity i 81% for battery A, and 76% for battery B. 50 minutes later, the remain capacity is 81% for battery A , 80% for batteryB, which means battery A remain capacity is same as before, while battery B remain capacity increase 4%! could

bq27z561 log.xls

over 1 year ago

0 Wyatt Keller over 1 year ago

TI__Guru** 104020 points

Hello Stone,

When the current falls below the Quit Current setting the gauge stops coulomb counting and starts to rely on the voltage. I suspect that the gauge entered into a rest state and then when a new OCV is taken the SOC is adjusted based on voltage. Battery A is much smaller so a smaller change in SOC with battery B would be larger change in battery A.

Sincerely,

Wyatt Keller

0 Stone Zeng over 1 year ago in reply to Wyatt Keller

TI__Prodigy 560 points

Hello Wyatt,

Thanks for your prompt reply. As showed from the log, the battery B voltage almost doesn't change when remain capacity increased from 76% to 80%, how to resolve this?

Stone

0 Wyatt Keller over 1 year ago in reply to Stone Zeng

TI__Guru** 104020 points

Hello Stone,

We do not know what happened directly before the log shared, there are scenarios which can cause error accumulation in CC, like constantly charging and discharge and never allowing for relaxation. The gauge will take an OCV measurement at rest and adjust the SOC based on the voltage.

Sincerely,

Wyatt Keller

0 Stone Zeng over 1 year ago in reply to Wyatt Keller

TI__Prodigy 560 points

Hi Wyatt,

which log do you need ? i would ask customer provide it for your further anaysis.

0 Wyatt Keller over 1 year ago in reply to Stone Zeng

TI__Guru** 104020 points

Hello Stone,

Do we know what tests were performed before this log? If they allow a relaxation and then do this test do they immediately see this behavior?

Sincerely,

Wyatt Keller

Power management

Power management forum

BQ27Z561-R1: two battery in parallel issue