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Ohm's law (I = V/R) to determine current based on the voltage drop across their terminals. To accurately determine the battery's SOC, shunt resistors need to be designed with good linearity and low- temperature coefficient resistance (TCR). Linearity is a measure of the change in current through the resistor that is proportional to the voltage measured across it. In other words, does the resistance change based on the applied current? Linearity is necessary to ensure reliable measurements that don't fluctuate across conditions. On the other hand, TCR is a measure of how much a resistor changes value as its temperature changes. To accurately determine the battery's SOH, shunt resistors need to change as little as possible with temperature (i.e., low TCR drift over time). For temperature sensing, a fundamental component is the NTC thermistor, a nonlinear resistor that exhibits a repeatable change in resistance with a change in temperature. The relationship between resistance and temperature is usually defined by the manufacturer and can be expressed with a curve-fitting formula. The NTC thermistor is often used in voltage dividers with another resistor of known value, in which the resulting output voltage can be plugged into the curve-fitting formula to determine the temperature. NTC thermistors also come in a variety of configurations, including surface-mount devices, lugs, and leaded versions. The configuration should be chosen such that the measurement is as close as possible to the battery element under monitoring (battery cells, cable, power board, etc.). For SOC measurements, NTC thermistors need high sensitivity and fast response C h a p t e r 2 | V o l t a g e , C u r r e n t , a n d T e m p e r a t u r e M e a s u r e m e n t s A lithium-ion battery is an electrochemical system in which temperature directly influences its chemical reaction. An ideal NTC for temperature measurement will have minimum drift over temperature, high accuracy, and good EMC performance." Jackie Hui Principal System Engineer, Automotive wBMS Solution, Analog Devices 10 8 Industry Experts Discuss Battery Management Solutions