The quality of the Kelvin connections at the sense resistor is critical. The sense resistor must have a temperature coefficient no greater than 50 ppm in order to minimize current measurement drift with temperature. Choose the value of the sense resistor to correspond to the available overcurrent and short-circuit ranges of the BQ76942 device. Parallel resistors can be used as long as good Kelvin sensing is ensured. The device is designed to support a 1-mΩ sense resistor.
In reference to the system circuitry, the following features require attention for component placement and layout: Differential Low-Pass Filter, and I2C communication.
The BQ76942 device uses an integrating delta-sigma ADC for current measurements. For best performance, 100-Ω resistors should be included from the sense resistor terminals to the SRP and SRN inputs of the device, with a 0.1-μF filter capacitor placed across the SRP and SRN pins. Optional 0.1-µF filter capacitors can be added for additional noise filtering at each sense input pin to ground. All filter components should be placed as close as possible to the device, rather than close to the sense resistor, and the traces from the sense resistor routed in parallel to the filter circuit. A ground plane can also be included around the filter network to add additional noise immunity.
The BQ76942 device internal REG18 LDO requires an external decoupling capacitor, which should be placed as close to the REG18 pin as possible, with minimized trace inductance, and connected to a ground plane electrically connected to VSS.
The I2C clock and data pins have integrated ESD protection circuits; however, adding a Zener diode and series resistor on each pin provides more robust ESD performance.