9.2.1.2.3 COMM, CLAMP, and BOOT Capacitors

For most applications, the COMM, CLAMP, and BOOT capacitance values will be chosen to match the bq51003EVM-764.

The BOOT capacitors are used to allow the internal rectifier FETs to turn on and off properly. These capacitors are from AC1 to BOOT1 and from AC2 to BOOT2 and must have a minimum 25-V rating. A 10-nF capacitor with a 25-V rating is chosen.

The CLAMP capacitors are used to aid in the clamping process to protect against overvoltage. These capacitors are from AC1 to CLAMP1 and from AC2 to CLAMP2 and must have a minimum 25-V rating. A 0.47-µF capacitor with a 25-V rating is chosen.

The COMM capacitors are used to facilitate the communication from the RX to the TX. This selection can vary a bit more than the BOOT and CLAMP capacitors. In general, TI recommends an 22-nF capacitor. Based on the results of testing of the communication robustness in the final solution, a change to a 47-nF capacitor may be in order. The larger the capacitor the larger the deviation will be on the coil which sends a stronger signal to the TX. This also decreases the efficiency somewhat. In this case, a 22-nF capacitor with a 25-V rating is chosen.