11.1 Layout Guidelines
Each system design and printed circuit board (PCB) layout is unique. The layout must be carefully reviewed in the context of a specific PCB design. However, the following guidelines can optimize the device performance:
- Connect the thermal pad to ground. Use a via pattern to connect the device thermal pad, the area directly under the device, to the ground planes. This connection helps dissipate heat from the device.
- The decoupling capacitors for the power supplies must be placed close to the device pins.
- The supply decoupling capacitors used must be of a ceramic type with low ESR.
- The boost converter inductor and decoupling capacitors for the power supplies must be placed close to the device pins.
- Route analog differential audio signals differentially on the PCB for better noise immunity. Avoid crossing digital and analog signals to avoid undesirable crosstalk.
- The device internal voltage references must be filtered using external capacitors. Place the filter capacitors near the VREF pin for optimal performance.
- Directly tap the MICBIAS pin to avoid common impedance when routing the biasing or supply for multiple microphones to avoid coupling across microphones.
- Place the MICBIAS capacitor (with low equivalent series resistance) close to the device with minimal trace impedance.
- Use MICBIAS and BSTOUT capacitors with a high voltage rating (> 25V) to support higher voltage MICBIAS operation.
- An external circuit must be used to suppress or filter the amount of high-frequency electromagnetic interference (EMI) noise found in the microphone input path resulting from long cables (if used) in the system.
- Use ground planes to provide the lowest impedance for power and signal current between the device and the decoupling capacitors. Treat the area directly under the device as a central ground area for the device, and all device grounds must be connected directly to that area.