SLUSBC8C December 2013 – July 2018
The current limit and foreign object detection functions are related. The current limit is set by R1 + RFOD. RFOD and Ros are determined by FOD calibration. Default values of 20 kΩ for Ros1 (RECT to FOD). Ros2 (OUT to FOD) remains open. 196 Ω for RFOD is used. The final values need to be determined based on the FOD calibration. The tool for FOD calibration can be found on the bq51003 web folder under Tools & software. Good practice is to set the layout with 2 resistors for Ros and 2 for RFOD to allow for precise values once the calibration is complete.
After setting RFOD, R1 can be calculated based on the desired current limit. The maximum current for this solution under normal operating conditions (IMAX) is 500 mA. Using Equation 2 to calculate the maximum current yields a value of 524 Ω for RILIM. With RFOD set to 196 Ω the remaining resistance for R1 is 328 Ω. This also sets the hardware current limit to 600 mA to allow for temporary current surges without system performance concerns.