BQ76PL455A Datasheet, PDF (103/125 Pages) Texas Instruments – 16-Cell Industrial Integrated Battery Monitor

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Application Information (continued)
GEC
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bq76PL455A
SLUSCL0A – SEPTEMBER 2016 – REVISED OCTOBER 2016
(14)
NOTE
The final GEC should be an 8-bit 2's-complement value in the range –128 to +127
after discarding the upper 8 bits of the 16-bit value. Values exceeding this are suspect
and probably indicate an error. If using such a value, saturate (–128 or +127) the
resulting 8-bit value and correct the sign as necessary.
This gain adjustment is input dependent—A correction of 9 mV at full-scale input,
results in a correction of 4.5 mV at half-scale input.
5. Write the 8-bit value to the VSGAIN register.
6. Perform the steps in Offset Error Correction.
8.1.3.2.2 Offset Error Correction
Offset Error Correction: –9.77 mV to 9.69 mV in 255 steps (8 bits) in register VSOFFSET
Procedure: (Use m, VIN1, and VOUT1 from the Gain Error Correction procedure.)
1. Find the offset error correction (OEC).
OEC
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(15)
NOTE
The final OEC should be an 8-bit 2's-complement value in the range –128 to +127 after
discarding the upper 8-bits of the 16-bit value. Values exceeding this are suspect and
probably indicate an error. If such a value must be used, the resulting 8-bit value should
be saturated (–128 or +127) and sign corrected as necessary.
2. Write the 8-bit value to the VSOFFSET register.
3. Save the new values to EEPROM by setting DEV_CTRL[WRITE_EEPROM], after setting the appropriate
values for MAGIC1 and MAGIC2. The EEPROM checksum will also require re-calculation and saving due to
this (or any) change.
8.1.3.3 AUX Channel Post-Assembly Calibration Adjustment
Using post-assembly calibration adjustment can also improve the AUX channel accuracy further after exposure
to soldering and/or bake cycles in the manufacturing process. The process is similar to the steps for the
VSENSE channel correction, with three differences:
• AUX channels only have offset correction, there is no gain correction.
• Each AUX channel has an individual offset correction register, rather than a single global correction.
• The correction range has an extension from –39.06 mV to 38.99 mV in 1023 steps (10 bits).
Perform the correction procedures at room temperature (RT) using a stable, high-accuracy DC source and / or
voltmeter. The registers contain 10-bit, signed, 2's-complement values. A zero value in any register indicates no
correction. Each correction measures two voltage points. The procedure can use the expected minimum and
maximum values for the cell. However, the lowest VIN_MIN value should be greater than or equal to 2.0 V and the
highest VIN_MAX should be less than or equal to 4.5 V.
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