ZHCSN81 july 2023 ADS131B23-Q1
PRODUCTION DATA
The 800-V battery-pack voltage is divided down to the voltage range of ADC2A using a high-voltage resistor divider, consisting of R1, R2, R3, R4, and R5. Gain = 1 is used for ADC2A in this case to allow differential voltage measurements of VIN2A = VV0A – VAGNDA = ±1.25 V. The battery-pack voltage measurement is a unipolar, single-ended measurement with the negative multiplexer channel of ADC2A internally connected to AGNDA. Thus, only the voltage range from 0 V to 1.25 V of ADC2A is used. Equation 23 calculates the resistor divider ratio.
The leakage current drawn by the resistor
divider should be less than 100 μA in this example to avoid unnecessarily draining the
battery. The resistance of the divider must therefore be larger than RTOTAL ≥
VBAT_MAX / ILEAKAGE = 800 V / 100 μA = 8
MΩ. The resistor values are chosen as R1 = R2 = R3 =
R4 = 2 MΩ and R5 = 12 kΩ. Thus, the maximum voltage across
R5 is 1.2 V at VBAT_MAX = 800 V, leaving some headroom to the
maximum input voltage of 1.25 V of ADC2A.
The maximum resistance of a single resistor that can be used in an automotive circuit design is often limited to a certain value. Also, the maximum voltage a single resistor can withstand is limited. These reasons are why the high-side resistor of the divider is split into multiple resistors (R1, R2, R3, and R4). Another reason is that in case a single resistor has a short-circuit fault, the remaining resistors still limit the current into the ADC2A analog input pin, V0A, to safe levels.