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Noise-sensitive Circuits

Non-sensitive Circuits

PCB Footprint Design

Thermal Performance

AN-894 08/23/15

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AN-894

APPLICATION NOTE

Table of Contents

Summary of Contents for IDT P9038

Page 1: Table Of Contents
P9038 Layout Guide AN-894 APPLICATION NOTE Contents (Click on any of the headings below to jump to that section) Using the Reference Layout ........................ 2 Importing the Reference Layout ........................2 Connecting a Power Source ......................... 3 Connecting Inputs / Outputs .........................
Page 2: Using The Reference Layout
Importing the Reference Layout The P9038-R-EVK reference design was created using Cadence PCB design software. This software has been used to generate layout modules which can be rapidly deployed onto PCB designs using Cadence OrCAD CIS and Cadence Allegro PCB Editor.
Page 3: Connecting A Power Source
PCB should be made with a minimum of 1oz copper foil weight per square foot or heavier. Additional Resources All support files and collateral for the P9038-R-EVK reference board can be found at http://www.idt.com/P9038-R-EVK. Files include: schematics, layout files, datasheets, user guides, etc.
Page 4: Custom Layout Guidelines
Custom Layout Guidelines The P9038 wireless power transmitter is an integrated device consisting of a high power full-bridge inverter designed to drive wireless LC resonance circuits and transmit power to WPC complaint wireless receivers. In addition to wireless power transfer, there are noise sensitive circuits, General Purpose I/O's (GPIO's) and two low power linear regulators.
Page 5: Power Circuits
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.
Page 6 RMS input current back to the power supply with minimal voltage drop along its length. Figure 4. P9038 Full-Bridge Inverter, Current Sense Resistor, and Resonance Tank Schematic. Note: not all pins are shown in the figure, refer to the P9038 datasheet Pin Description for the complete list of pins and recommended connections)
Page 7: Input Capacitors
VIN/SW1/SW2 pins). The ideal placement of the input capacitors is to have them as close as possible to the P9038 device and symmetrically placed so that the wiring and connections are matched relative to the IN_x pins (QFN pins 34, 35, 36, 37) and the PGND1 &...
Page 8 Figure 6. P9038 2-Layer Layout Critical VIN to SW1/SW2 Current Paths from Input Capacitors It should be noted that the 0.1µF capacitor C18 is located the closest to the P9038 device because the lower capacitance and ESL of the smaller package allow it to filter higher frequencies more effectively than physically larger components. Since these are the highest priority signals to filter, it is imperative that the impedance from this component to IN and PGND is minimized.
Page 9: Bst And Zvs Capacitors
P9038-R-EVK. It is recommended to keep the SW1 and SW2 signals on the same physical side of the PCB as the P9038 and make VIN switch layers since the SW1/2 signals are AC and more sensitive to vias and layer transfers than the relatively stable (DC + ripple) VIN current.
Page 10 Next, the current sense resistor and the associated filters are crucial for Foreign Object Detection (FOD) accuracy, as they impact the input power calculations. The P9038 calculates the input power using the voltage on the IN pins and the current detected as a voltage drop across the sense resistor (R2).
Page 11: Epad
EPAD The use of a grid of 25 thermal vias placed inside the E-PAD of the P9038 device is recommended. Using thermal vias and having one or more GND planes in direct contact is crucial for optimal thermal performance. Typical thermal via diameter is 0.3mm and spacing should be 1mm pitch.
Page 12: Noise-Sensitive Circuits
Noise-sensitive Circuits The sensitive circuits refer to noise sensitive circuits that should be referenced to GND on the side of the P9038 that is furthest from the PGND pins and input capacitors ("Quiet GND" side). They include the Input current sense filters (previously discussed), the ISNS_AVG pin (pin 48 for the QFN) connection to capacitor (C47), the LDO pins and filter capacitors, VSNS_AVG (Pin24) plus capacitor C51, REFGND (pin 17) and the DEMOD WPC communication filters.
Page 13: Non-Sensitive Circuits
AN-894 Figure 11. Sensitive DEMOD, Rsns Filter, LDO GND Located on opposite side of the P9038 from the PGND pins. Provide GND connection directly to EPAD for these GNDs. The current sense connections from R2 to R3 and R4 are done in a Kelvin manner, directly to the pins of R2. This is done to get the most accurate voltage drop across the sense resistor prior to filtering and amplification by the internal differential amplifier used to help calculate input power for FOD.
Page 14: Thermal Performance
Thermal Performance PCB design can have a substantial impact on operating temperature and efficiency. In order to allow the P9038 to operate at the lowest possible temperature, the EPAD must be connected directly to a GND plane and traces on the bottom layer should be kept as short as possible and be routed as far away from the EPAD as possible to promote heat flow paths and heat dissipation.
Page 15 AN-894 Figure 13. P9038-R-EVK Bottom Layer Heat Flow Paths and Thermal Image when delivering 5 W to the P9025AC-R-EVK (board is 2.1" x 1.134" in area near the application circuitry). Metallic Surfaces Appear Cooler than they are due to their Emissivity.
Page 16 IDT or any third parties. IDT’s products are not intended for use in applications involving extreme environmental conditions or in life support systems or similar devices where the failure or malfunction of an IDT product can be reasonably expected to significantly affect the health or safety of users.

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P9038-r-evk