BQ76952: current measurement accuracy was not good when -10 degree

Statham Su

Genius 4990 points

Part Number: BQ76952
Other Parts Discussed in Thread: 4430

Hello Sir:

We had been tested our PCBA.

But we found the current measurement results was not good when 0 degree and -10 degree.

Please refer below block diagram and tested results.

Tested results

When -10 degree.

Item	Charging				Item	Discharging
	Meter	GUI (cc3)	ERROR			Meter	GUI (cc3)	ERROR
	mA		A	%		mA		A	%
1A	999	980	19	1.94	5A	5004	4810	194	4.03
1.5A	1499	1470	29	1.97	10A	10001	9670	331	3.42
2A	1999	1950	49	2.51	20A	20011	19400	611	3.15
2.5A	2499	2440	59	2.42	30A	30007	29140	867	2.98
3A	3003	2930	73	2.49	40A	40006	38920	1086	2.79
3.5A	3504	3420	84	2.46	50A	50001	48740	1261	2.59
4A	4004	3900	104	2.67	60A	60019	58620	1399	2.39
4.5A	4503	4390	113	2.57	70A	69995	68570	1425	2.08
5A	5003	4880	123	2.52	80A	80065	78640	1425	1.81
5.5A	5501	5360	141	2.63	90A
5.8A	5801	5650	151	2.67	100A

When 0 degree

Item	Charging				Item	Discharging
	Meter	GUI (cc3)	ERROR			Meter	GUI (cc3)	ERROR
	mA		A	%		mA		A	%
1A	1003	990	13	1.31	5A	5005	4860	145	2.98
1.5A	1499	1490	9	0.60	10A	10001	9760	241	2.47
2A	1997	1980	17	0.86	20A	20011	19600	411	2.10
2.5A	2501	2460	41	1.67	30A	30013	29420	593	2.02
3A	3004	2960	44	1.49	40A	40003	39310	693	1.76
3.5A	3504	3450	54	1.57	50A	50004	49210	794	1.61
4A	4003	3940	63	1.60	60A	60027	59170	857	1.45
4.5A	4503	4430	73	1.65	70A	69983	69250	733	1.06
5A	5003	4920	83	1.69	80A	80070	79250	820	1.03
5.5A	5501	5420	81	1.49	90A
5.8A	5801	5700	101	1.77	100A

When 25 degree.

Item	Charging				Item	Discharging
	Meter	GUI (cc3)	ERROR			Meter	GUI (cc3)	ERROR
	mA		A	%		mA		A	%
1A	999	1010	-11	-1.09	5A	5003	4960	43	0.87
1.5A	1499	1510	-11	-0.73	10A	9970	10001	-31	-0.31
2A	1997	2020	-23	-1.14	20A	20011	19970	41	0.21
2.5A	2497	2510	-13	-0.52	30A	30012	29990	22	0.07
3A	3004	3020	-16	-0.53	40A	40005	40040	-35	-0.09
3.5A	3499	3520	-21	-0.60	50A	50002	50140	-138	-0.28
4A	4003	4020	-17	-0.42	60A	60024	60250	-226	-0.38
4.5A	4503	4520	-17	-0.38	70A	69983	70540	-557	-0.79
5A	5003	5020	-17	-0.34	80A	80069	80840	-771	-0.95
5.5A	5501	5520	-19	-0.34	90A
5.8A	5801	5820	-19	-0.33	100A

When 40 degree.

Item	Charging				Item	Discharging
	Meter	GUI (cc3)	ERROR			Meter	GUI (cc3)	ERROR
	mA		A	%		mA		A	%
1A	1003	1020	-17	-1.67	5A	5003	5020	-17	-0.34
1.5A	1499	1520	-21	-1.38	10A	10001	10090	-89	-0.88
2A	2001	2030	-29	-1.43	20A	20011	20240	-229	-1.13
2.5A	2501	2550	-49	-1.92	30A	30013	30390	-377	-1.24
3A	3004	3060	-56	-1.83	40A	40003	40580	-577	-1.42
3.5A	3504	3560	-56	-1.57	50A	50001	50790	-789	-1.55
4A	4003	4070	-67	-1.65	60A	60023	61110	-1087	-1.78
4.5A	4503	4580	-77	-1.68	70A	69981	71110	-1129	-1.59
5A	5003	5080	-77	-1.52	80A	80069	81300	-1231	-1.51
5.5A	5501	5590	-89	-1.59	90A
5.8A	5801	5900	-99	-1.68	100A

Would you please teach us how to improve the current measurement accuracy when 0 and -10 degree?

Looking forward your feedback.

Thanks a lot.

over 2 years ago

0 Luis H. S. over 2 years ago

TI__Mastermind 42060 points

Hello Statham,

What sense resistor are they using?

There are many factors that affect the current error. Which are all listed in Section 7.15 Coulomb Counter of the datasheet. There is some explanation on the calculation and other considerations in the following e2e thread: (19) BQ76952: Maximum uncalibrated current measurement accuracy - Power management forum - Power management - TI E2E support forums

Assuming the worst-case scenarios for all of these errors, assuming a 1-mOhm resistor and assuming you use a current of 5-A. At -10C the expected maximum possible error is ~226-mA or 4.5%.

The e2e thread I linked may be useful to know how to try to minimize the error, especially if this is consistent in multiple boards.

Best Regards,

Luis Hernandez Salomon