BQ25887: BQ25887 Charging Current Measurements

Oleg,

Can you please elaborate on your measurement setup? Is this on the EVM? Where are you measuring? What equipment are you using to measure?

Thanks,

Ricardo

1. Unfortunately I do not have the EVB. So this is on my own PCB.

2. I measure current through higher battery (see the picture #1).

3. I connected two multimeters in series: UNI-T UT61E and RIGOL DM3061. Both give me the same results (see the picture #2).

4. BQ25887 registers and the decoded value for Ichg are on picture #3.

It is 21% lower than measured value

Oleg,

Have you measured the going across the CBSET resistor? I suspect some current may be going through that path as your VTOP and VBOT are significantly different.

Thanks,

Ricardo

1. VTOP and VBOT are different because of two multimeter's resistance connected in series.

2. I guess if some current goes through CBSET resistor than measured current would be less but not greater.

3. I achieved some progress by connecting 0.01 uF capasitor at SNS pin in addition to 44 uF recommended in datasheet. Now the current difference is 6-7% and it is close to 0% at currents lower then 500 mA. But that is the best result for now. Combining different capasitors from 1 nF to 1 uF I never got accurate current measurements at 1 A or higher current.

Oleg,

I will be looking into this today in the lab to see if I can recreate the inaccuracy on the EVM.

Thanks,

RIcardo

Thanks for the help.

Now I know that the problem is in my design. I will try to measure current with a low resistance sence resistor and try other components and PCB trace configurations.

I will write here if there are new results.