TIDUF88 October 2024
3.3.2 Current Sensing Accuracy
The test setup follows Figure 3-1. A high-precision voltage source provides eleven voltage test points from –75mV to 75mV to simulate shunt current range from –500A to 500A in a 150μΩ shunt. To verify the current resolution of the current sensing circuit, 1500μV (10A across the 150μΩ shunt) is applied.
Table 3-11 shows the current sensing accuracy data measured with BQ79731 CSADC1. The maximum error before calibration is 58.79μV. The maximum error after calibration is 9.87μV. Assuming the shunt resistance is 150μΩ, after calibration, the current accuracy is less than 0.007% when shunt current > 10A, and maximum 6.56mA absolute error when shunt current ≤ 10A.
| Simulator_ voltage (μV) |
CSADC1 ACCURACY BEFORE CALIBRATION |
CSADC1 ACCURACY AFTER CALIBRATION |
SHUNT CURRENT
SENSING |
||||
|---|---|---|---|---|---|---|---|
| CSADC1_ Reading_ uncal (μV) |
CSADC1_ uncal_ error (μV) |
CSADC1_ reading_cal (μV) |
CSADC1_cal_ error (μV) |
Error (%) | 150μΩ SHUNT CURRENT ERROR (mA) |
150μΩ SHUNT CURRENT (A) |
|
|
–75000 |
–74941.21 |
58.79 |
–74990.13 |
9.87 |
–0.0001 |
65.82 |
–500.00 |
|
–2500 |
–2490.96 |
9.04 |
–2501.08 |
–1.08 |
0.0004 |
–7.20 |
–16.67 |
|
–1500 |
–1491.40 |
8.60 |
–1500.98 |
–0.98 |
0.0007 |
–6.56 |
–10.00 |
|
–250 |
–242.07 |
7.93 |
–250.99 |
–0.99 |
0.0039 |
–6.58 |
–1.67 |
|
–150 |
–142.01 |
7.99 |
–150.87 |
–0.87 |
0.0058 |
–5.77 |
–1.00 |
|
0 |
8.78 |
8.78 |
0.00 |
0.00 |
NA |
0.03 |
0.00 |
|
150 |
159.25 |
9.25 |
150.56 |
0.56 |
0.0037 |
3.70 |
1.00 |
|
250 |
259.37 |
9.37 |
250.73 |
0.73 |
0.0029 |
4.85 |
1.67 |
|
1500 |
1507.90 |
7.90 |
1499.92 |
–0.08 |
–0.0001 |
–0.52 |
10.00 |
|
2500 |
2507.21 |
7.21 |
2499.77 |
–0.23 |
–0.0001 |
–1.54 |
16.67 |
|
75000 |
74968.64 |
–31.36 |
75000.00 |
0.00 |
0.0000 |
0.03 |
500.00 |
Figure 3-3 shows the shunt voltage accuracy curve measured with BQ79731 CSADC1.
Figure 3-3 CSADC1 Accuracy Curve