BQ40Z60: Series resistor value at ACP pin

Hi Sergey,
The 10k resistor is part of a voltage divider (10k/(10k+100k)) on ACP pin to ensure ~0.9V ( less than 1V Max) input to the ADC, that's why we have 10k resistor.
Best,
Haidar
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Hi Haidar,

do you mean 100kOm is an internal resistor in BQ40Z60? Such a divider couldn't guarantee 1Vmax output with 26Vmax input. Data sheet states it a bit differently:

Anyway, I can see neither 40 nor 100. In fact just about 200mV drops at 10kOhm with Vacp=12V, which suggests about 600kOhm internal resistor (if there is any). This dropout varies with time (mode?) and input voltage and likely serves a source of inaccuracy, which I observe. Calibration brings no relief. Meanwhile battery voltages measurements are quite accurate.

Please re-check your information. Of course, if 10kOhm is really an intended value for some reason, I would have to give up.

Regards,

Sergey

RPD

Internal pulldown resistance

ACP

30

40

50

kΩ

Above is an extract from data sheet which I unsuccesfully tried to paste directly in the previous post.

Regards,

Sergey

Hi Sergey,
I apologize if I have confused you, the 10k external resistor with the 40k (Typ.) internal resistors not (100k I mentioned before) is a voltage divider to ensure scaling charger input voltage to the ACP pin. This is the first scaling stage for VACP then VACP gets scaled internally by ADC MUX so that the ADC can read VACP (Sample) scaled to 1V Max .
Best,
Haidar

Hi Haidar,

thank you, this explanation seems to have better ground. Nevertheless, as far as I can see, actual behavior doesn't prove this model.

Please consider the below data

Vacp, mV	Charger enabled		Charger disabled
	Vacp measured	drop@10k	Vacp measured	drop@10k
10003	9771	203	10014	25
11998	11769	206	11996	28
14995	14770	209	14973	33
20045	19736	216	19968	40

 Note: Vacp channel was calibrated at 12V with charger disabled.

This data suggests that major contributor to the drop voltage at 10kOhm resistor is probably charge pump supply current.

As to ACP pin pulldown resistor, it may have been switched off when Vacp present, or at least it should be about 5MegOhm to explain few millivolts drop at 10kOhm resistor with disabled charger.

To have measurements more accurate the drop at 10kOhm resistor should be made minimal (or constant). This is why I ask of possible contra-indications to reducing 10kOhm to 1kOhm or so.

Regards,

Sergey

Ok, thanks.

Sergey