10.1 Layout Guidelines

• The traces connecting pins CFA and CFB to the CF capacitor should be as short as possible to minimize the parasitic capacitance.
• The NTC should be placed as close to the LC tank as possible to minimize error introduced by temperature variation within the operating environment. The NTC should also be close to the LMP91300 to minimize the parasitic capacitance. There should be a ground trace separating the thermistor from the LC tank, to minimize the coupling from the signal on the LC tank. Ideally, the thermistor could be on one side of the PCB and the LC tank on the other side of the PCB with a ground plane between them.
• There should be a ground trace between the INA and INB terminals and the rest of the terminals of the LMP91300 to decrease the coupling of the signal on the INA and INB terminals to the other terminals of the LMP91300. The trace between the LC tank and the INA and INB terminals should be as short as possible as shown in part A of Figure 24. Longer traces between the LC tank and the INA and INB terminals can cause ringing at the INA and INB terminals which can produce very noisy proximity readings. If longer traces need to be used split the LC tank so that the capacitor is close to the LMP91300 as shown in part B of Figure 24. If both the L an C have to be located a longer distance away from the LMP91300 small capacitors (15 to 22pF) can be connected between INA and ground and INB and ground as shown in part C of Figure 24.
• Keep the trace between the SWDRV terminal and the transistor short.
• The DAP area on the PCB can be used as the center of a star ground with all other ground terminals connecting to it.

10.2 Layout Example

Figure 28. LMP91300 PNP Layout Example