JAJSML5A March 2022 – August 2022 ADS131M04-Q1
PRODUCTION DATA
The 800-V battery-pack voltage is divided down to the voltage range of the ADS131M04-Q1 using a high-voltage resistor divider (RH1, RH2, RH3, and RL). Gain = 1 is used for channel 0 in this case to allow differential voltage measurements of VIN0 = VAIN0P – VAIN0N = ±1.2 V. The battery-pack voltage measurement is a unipolar, single-ended measurement. Thus, only the voltage range from 0 V to 1.2 V of the ADS131M04-Q1 is used. Equation 11 calculates the resistor divider ratio.
The leakage current drawn by the
resistor divider must 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
RH1 = RH2 = RH3 = 2.8 MΩ and RL =
12.4 kΩ. Thus, the maximum voltage across RL is 1.18 V at
VBAT_MAX = 800 V, leaving some headroom to the maximum input voltage
of 1.2 V of the ADS131M04-Q1.
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 (RH1, RH2, and RH3). Another reason is that in case a single resistor has a short-circuit fault, the remaining resistors still limit the current into the ADS131M04-Q1 analog input pin (AIN0P) to safe levels.