Analog Devices' AD1845 Parallel-Port, 16-Bit, Sound-Port Stereo Codec is pin-for-pin compatible with Crystal Semiconductor's CS4231 Multimedia Audio Codec. However, customers have faced difficulties using them interchangeably due to slightly different external interface requirements and power supply circuitry recommendations. This document addresses these challenges by showing designers how to create a compatible PCB layout or 'socket' for both parts within PC motherboard or plug-in card designs.
The note details specific design considerations including input circuit design, power supply strategies (both recommended and alternative), and layout principles such as component placement and grounding. It also covers cost/performance tradeoffs that allow for a socket requiring no assembly differences between the two codecs.
The main differences involve external interface requirements, specifically crystal oscillator inputs (CS4231 requires two crystals while AD1845 uses one) and differing power supply circuitry recommendations.
The CS4231 requires two crystal inputs (XTAL1 at 24.575 MHz and XTAL2 at 16.9344 MHz), whereas the AD1845 defaults to a single crystal input (24.576 MHz) but can use other frequency sources.
For best performance in a compatible socket, the AD1845 requires 1 µF capacitors on the external filter pins, while the CS4231 uses 1000 pF capacitors.