Finally, the reference’s initial accuracy and temperature coefficient parameters are important, although they do not influence accuracy as much as the reference voltage.
The Component Selection
Once again, the Freescale Semiconductor K10P64M72SF1 microcontroller is used. The MAX6034B voltage reference was selected for its price point as well as its 13mV initial accuracy and 75ppm/°C (max) temperature drift. It also has a 3.3V option, which the selected microcontroller will accept and which greatly improves accuracy compared to a 1.195V reference used in the cost-optimized example above (Figure 5).
Selecting R 1 = 1MΩ and R 2 = 213kΩ with 0.1% tolerance, the maximum error introduced by the voltage-divider is 3.55mV.
The cost-optimized, accuracy-enhanced architecture using the Freescale Semiconductor K10P64M72SF1 and the MAX6034B voltage reference achieves six-sigma error as low as 31.154mV and three-sigma error as low as 17.632mV. Compared to the cost-optimized architecture discussed above, this example design offers an 87.6% decrease in six-sigma error with only a minor increase in the cost of the system.
Four architectures have been outlined to give system designers flexibility in implementing battery-management systems. In all cases the MAX14921 (or MAX14920) was the optimal AFE capable of delivering high-performance battery monitoring and cell-balancing capabilities for multiple design constraints. The selection of ADC, reference, and microcontroller will depend on the accuracy-cost trade-off.
1 If the MAX6194 reference is used in