08/23/15
5
P9038 LAYOUT GUIDE
AN-894
Power Circuits
The integrated Full-Bridge Inverter and the resonance tank are the primary power circuits. Secondary power circuits are the
LDO5V and LDO2P5V voltage regulators. After the connection points for the transmitter coil (LTX) are chosen, the P9038 should
be placed as close to the center of the PCB as possible with SW1 and SW2 pins facing the LC resonance tank. Components
should be placed in the following order of priority:
1. Input capacitors (C
IN
)
2. BST1, BST2 capacitors
3. Resonance tank (C
P
and L
TX
)
4. Zero Voltage Switching (ZVS) capacitors and tuning resistors
5. LDO capacitors
6. Current Sense Resistor (R
SENSE
)
7. Optional USB input transistor (USB FET, see Application Note
AN-867 P9038 OVP and In-Rush Current Limiting
Options
for additional details)
8. Current sense filter components
Figure 3. P9038 Physical Layout from REFERENCE PCB (2 layer PCB), Main Power Sensitive Circuits
demonstrates the key nodes and layout recommendations for a 2-layer PCB. Important concepts include CIN direct
routing to IN and PGND pins and wide connections (>=60mils) for VIN. SWx nodes are routed on P9038 side of the PCB and
can easily be extended directly out for PCBs that have more distance to the edge of the board. LDO5V and LDO2P5V capacitors
are located very close to the IC with direct GND return to the EPAD. The EPAD has 25 thermal vias. Traces located on the bottom
layer have been placed as far as possible from the EPAD to create heat flow 'channels' (see the top left and lower regions
surrounding the EPAD on the bottom layer). Solid and continuous GND planes in direct contact with the EPAD will result in lower
operating temperatures and higher efficiency.
