The RES60A-Q1 can be used in conjunction with an automotive precision amplifier, such as the OPA192-Q1, for single-ended measurement of the high side (BAT+) of an EV battery relative to a fixed potential. For those systems where BAT– and GND are equivalent, as in Figure 7-1 (a), the configuration shown in Figure 7-2 applies. An alternative approach is to measure directly across the battery from BAT+ to BAT–, as shown in Figure 7-3. This approach is useful for systems referenced to the low side of the battery, BAT–, as in Figure 7-1 (b).

Figure 7-1 Common Battery and System Configurations

Figure 7-2 Single-Ended Measurement, BAT+ to GND

Figure 7-3 Single-Ended Measurement, BAT+ to BAT–

For some system architectures, BAT– floats relative to the chassis GND; see also Figure 7-1 (c). If for example a microcontroller referenced to chassis ground needs to measure the voltage across the entire battery stack, a difference amplifier can be constructed using two RES60A-Q1 devices and an OPA192-Q1. Figure 7-4 shows this approach. If two ADC channels are available, two single-ended measurements can be done using two RES60A-Q1 devices and an OPA2192-Q1.

Figure 7-4 Differential Measurement, BAT+ to BAT–

Leakage in the system and quiescent current from the amplifier input reduce the precision of the measurement. In some cases, a guard buffer can be used to reduce leakage currents. Follow best practices to reduce board contamination and leakage.

For an 800V single-ended battery measurement (see also Figure 7-2), the static current through the divider is:

Therefore, the buffer amplifier used must have a low bias current, such that I_B << I_STATIC. The low bias current of the OPA192-Q1 (5pA typical at 25°C, 5nA maximum from –40°C to +125°C) makes the device an excellent choice for this role.