10.1 Layout Guidelines
A minimum of two layers is required to a accomplish a small-form factor ultrasonic module design. The layers should be separated by analog and digital signals. The pin map of the device is routed such that the power and digital signals are on the opposing side of the analog driver and receiver pins. Consider the following best practices for PGA460-Q1 device layout in order of descending priority:
- Separating the grounding types is important to reduce noise at the AFE input of the PGA460-Q1. In particular, the transducer sensor ground, supporting driver, and return-path circuitry should have a separate ground before being connected to the main ground. Separating the sensor and main grounds through a ferrite bead is best practice, but not required; a copper-trace or 0-Ω short is also acceptable when bridging grounds.
- The analog return path pins, INP and INN, are most susceptible to noise and therefore should be routed as short and directly to the transducer as possible. Ensure the INN capacitor is close to the pin to reduce the length of the ground wire.
- In applications where protection from an ESD strike on the case of the transducer is important, ground routing of the capacitor on the INN pin should be separate from the device ground and connected directly with the shortest possible trace to the connector ground.
- The analog drive pins can be high-current, high-voltage, or both and therefore the design limitation of the OUTA and OUTB pins is based on the copper trace profile. The driver pins are recommended to be as short and direct as possible when using a transformer, and driving the primary windings with a high-current limit
- The decoupling capacitors for the AVDD, IOREG, and VPWR pins should be placed as close to the pins as possible
- Any digital communication should be routed away from the analog receiver pins. The IO, TXD, RXD, and SCLK pins should be routed on the opposite side of the PCB, away from of the analog signals. When the IO pin is referenced to a high-voltage VPWR, and operating at a high-speed baud rate, the trace to the connector or master should be as direct as possible