Abstract: This article describes how to interface the DS1863, DS1865, or DS1875 PON controller/monitor circuits to a compact laser driver. The MAX3736 or MAX3741 are the SFP laser drivers used in this application. The controllers provide SFF-8472-compliant digital diagnostics, laser calibration, laser control, and power leveling functionality. The Controllers The DS1863, DS1865, and DS1875 controllers provide two outputs for controlling the laser driver: BIAS and MOD. BIAS is a 13-bit current DAC with a full-scale range of 1.2mA. The MOD output is an 8-bit voltage DAC with a full-scale range of 1.25V. The Compact Laser Driver The MAX3736 or MAX3741 laser driver has two inputs for laser control: BIASSET and MODSET. Both inputs should be connected to a current-sink controller with 1.2mA full-scale range in order to utilize the laser driver's full output range. Interface Between Controller and Laser Driver The controller's BIAS output provides the correct range for the BIASSET input of the laser driver. The MOD output is voltage mode, so must be adapted to interface to the laser driver (Figure 1). Voltage-to-Current Conversion An operational amplifier and NPN transistor are used to create a 1.2mA full-scale output from the MOD voltage-DAC output. The MOD output ranges from 0V to 1.25V. The NPN needs to sink current from the MODSET pin, which is maintained at 1.2V. R1 is chosen to keep the voltage at the NPN's emitter to less than 0.3V, and this ensures that the NPN does not saturate at full-scale current. The maximum full-scale current sunk by the NPN is set by the equation: IMAX = R2 × 1.25V/(R1 × (R3 + R2)). Figure 1. Controller-to-laser-driver interface. Component Selection This application does not require special components. A generic operational amplifier and NPN transistor can be used; the smallest, most affordable components will perform adequately in this application. The Maxim LMX321AXK-T operational amplifier is available in a 2.1mm x 2.0mm SC70-5 package. An NPN such as a 2N3904 or 2N2222 is also sufficient. Conclusion A small, simple, inexpensive circuit can be used to interface the DS1863, DS1865, or DS1875 PON controller/monitor to a compact laser driver. This interface circuit can be implemented in less than 9mm². 의견을 보내주세요! 위 내용이 도움이 되셨나요? 여러분의 의견을 기다립니다 — Maxim은 보내주신 정정이나 제안사항을 반영하고 있습니다. 이 페이지를 평가하고 의견을 보내주십시오. 자동 업데이트 관심있는 분야의 애플리케이션 노트가 나올 때 자동으로 업데이트 받고 싶으세요? 그렇다면 EE-Mail™을 신청하십시오. 추가 정보   APP 4222: Jun 06, 2008 DS1863 모니터링 기능이 내장된 버스트 모드 PON 컨트롤러 전체 데이터 시트 (PDF, 788kB) 무료 샘플 DS1865 PON 트리플렉서 제어 및 모니터링 회로 전체 데이터 시트 (PDF, 532kB) 무료 샘플 DS1875 PON 트리플렉서 및 SFP 컨트롤러 전체 데이터 시트 (PDF, 2.6MB) MAX3736 3.2Gbps, 저전력, 초소형의 SFP 레이저 드라이버 전체 데이터 시트 (PDF, 348kB) 무료 샘플 MAX3741 초소형의 3.2Gbps, SFP VCSEL 드라이버 전체 데이터 시트 (PDF, 292kB)   다운로드, PDF 형식 (31kB)  AN4222, AN 4222, APP4222, Appnote4222, Appnote 4222