BQ24725A: WHAT'S THE TERMINATE CURRENT?

Howard Zou

Part Number: BQ24725A
Other Parts Discussed in Thread: BQ4050

Hi,

1. I can't find the spec of terminate current of the device?

Is it configurable? Or is it related to the charge current value?

2. Are there any side effect if we switch between IOUT selection=1(charge current sensing) and 0(adaptor current sensing) frequently like 1Hz?

3. My customer tested with Iout to sense the charge current and IOUT pin is connected to ADC of MCU, and the charge current read by gauge BQ4050 and multimeter are both 750mA, but MCU read the current to be 896mA, the error is about 19%, which exceeds the spec in the datasheet (sense resistor=10mOhm, the same as in the datasheet). What may cause the problem?

charge current read by gauge/multimeter	charge current read by MCU through IOUT pin
750mA	896mA
151mA	281mA

over 5 years ago

0 Howard Zou over 5 years ago

TI__Genius 12365 points

3. IOUT voltage is 179mV by multimeter when the charge current read by gauge is 750mA.

179mV➗20➗10mOhm=895mA。

So the error is not caused by MCU's ADC but the current sense amplifier.

0 Joel Hernandez II over 5 years ago in reply to Howard Zou

TI__Mastermind 25800 points

Hey Howard,

1. This charger does not terminate because it is Host controlled. The host manages the entire charge profile including the maximum charge voltage, the charging current based on the battery voltage, and even terminating charge.

2. I don't forsee an issue with changing the setting every second. It is only a buffered output.

3. This is within the specification of the IOUT pin. The specification is seen below, and is a function of the differential voltage across SRx or ACx sense resistor. In this case, VSRP-VSRN is 7.5mV

Regards,

Joel H

0 Howard Zou over 5 years ago in reply to Joel Hernandez II

TI__Genius 12365 points

Joel,

the latest data we got are as below:

current read by gauge	current read by MCU through IOUT
809	896
216	281
39	87
0(charge disabled)	50

I know the error is within spec, but do we have anyway to minimize the error?

0 Howard Zou over 5 years ago in reply to Howard Zou

TI__Genius 12365 points

Hi Joel,

waiting for your reply, thanks.

0 Joel Hernandez II over 5 years ago in reply to Howard Zou

TI__Mastermind 25800 points

Hey Howard,

This error can be reduced with an increased RSR resistor to a value like 20mOhm, instead of 10mOhm. This will limit the charging current as every value will scale by 1/2, but it should improve the accuracy somewhat.

Regards,

Joel H

Power management

Power management forum

BQ24725A: WHAT'S THE TERMINATE CURRENT?