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Board layout guidelines all recommend that designers keep everything short, keep the traces short, keep loops small and nothing is different for the Power XR products in that regard. However there are four channels and the designer might not want to put every single channel right around the chip. Some of the other things that are specific to the XRP77xx family is that the power ground should not be connected at the chip. This is actually one of the nodes for the current sensing. Current is sensed on the low side fet, RDS on sensing, so that should actually be connected to the source of the low side MOSFET, where the MOSFET is mounted on the board. Do not connect it through the ground plane, consider the four power grounds as actual signals rather than as an actual ground. The other node for the current sensing is the LX node. The XRP7724 has taken a step to clarify the role of the power ground pins by naming them gate low return.

PTM Published on: 2013-09-19