The quality of the Kelvin connections at the sense resistor is critical. The sense resistor should have a temperature coefficient no greater than 50ppm 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 BQ76907-Q1 device. Parallel resistors can be used as long as good Kelvin sensing is ensured.
In reference to the system circuitry, the following features require attention for component placement and layout: differential low-pass filter and I2C communication.
The BQ76907-Q1 device uses an integrating delta-sigma coulomb counter ADC for current measurements. For best performance, 100Ω resistors should be included from the sense resistor terminals to the SRP and SRN inputs of the device, with a 0.1μF filter capacitor placed across the SRP and SRN pins. Optional 0.1µF 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.
These filter components between the sense resistor and the SRP and SRN terminals provide filtering of noise components, but they also introduce an RC time constant delay, nominally 20µs using the two 100Ω and single differential 0.1μF components. If this delay introduces too much additional time into the response of the device to short circuit events, the filter time constant can be reduced, with the tradeoff of providing less filtering.
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.