JAJSL33A june 2020 – january 2021 BQ25731
PRODUCTION DATA
The BQ25731 has average current mode control. The input current sensing through ACP/ACN is critical to recover inductor current ripple. Parasitic inductance on board will generate high frequency ringing on ACP-ACN which overwhelms converter sensed inductor current information. It is also difficult to manage parasitic inductance created based on different PCB layout. Larger parasitic inductance will generate larger sense current ringing which could cause the average current control loop to go into oscillation. Therefore ACP-ACN sensing information need to be conditioned.
For real system board condition, we suggest using below circuit design to get best result and filter noise induced from different PCB parasitic factor. With time constant of filter from 47 ns to 200 ns, the filter is effective and the delay of on the sensed signal is small, therefore there is no concern for average current mode control. If 400-kHz switching frequency is employed, 10 nF is recommended for CDIFF; if 800-kHz switching frequency is chosen, then CDIFF can be left open.