原标题：Allegro A5303新标准3V光电烟雾检测方案

　　Allegro 公司的A5303是低功耗BiCMOS光电烟雾检测电路，具有超低待机电流，采用便宜电池也能工作10年。工作电压2.3 到5.5 V，其可变增益光放大器直接和红外发射-检测对接口，而内置电路可降低误触发，内部的振荡器和时序电路每10秒仅用100us检测烟雾，因而是待机功耗最低化。本文介绍了A5303主要特性和优势以及方框图与典型应用电路。

　　The A5303 is a low-current BiCMOS photoelectric smoke detector circuit with ultra-low standby current and can operate for 10 years powered by inexpensive batteries. This device can be used with an infrared optical chamber to sense light scattered from smoke particles. A networking capability allows units to be interconnected so that if any unit senses smoke all units will sound an alarm. Special features are incorporated in the design to facilitate calibration and testing of the finished detector.

　　A variable-gain photoamplifier can be directly interfaced to an infrared emitter-detector pair. The amplifier gain levels are determined by two external capacitors and are internally selected depending on the operating mode. Low gain is selected during standby and timer modes. During a local alarm, this low gain is increased (internally) by approximately 45% to provide hysteresis. High gain is used during pushbutton test and to periodically monitor the chamber sensitivity during standby.

　　The internal oscillator and timing circuitry minimize standby power by sensing for smoke for only 100 μs once every 10 s. A special three-stage-speedup sensing scheme is incorporated to minimize the time to an audible alarm and also to reduce false triggering. Chamber sensitivity is periodically monitored and two consecutive cycles of degraded sensitivity are required for a warning signal to occur.

　　The A5303 is supplied in a thin profile (<1.2 mm overall height) 20-pin TSSOP package (0.65 mm nominal lead pitch). The package is lead (Pb) free with 100% matte tin leadframe plating.

　　A5303主要特性和优势：

　　▪ Low average standby current allows 10-year battery life

　　▪ 2.3 to 5.5 V operating range

　　▪ Interconnect option

　　▪ Logic outputs to control an external sound IC

　　▪ Low battery detection and warning

　　▪ Chamber sensitivity test and warning

　　▪ Triple horn-chirp to distinguish chamber warning

　　▪ Power-on reset (POR)

　　▪ Digital filter on I/O provides significant noise immunity

　　▪ Timer (hush) mode for enabling reduced sensitivity period

　　▪ Built-in circuits to reduce false triggering

　　▪ ESD protection circuitry on all pins

　　▪ Temporal Horn Pattern, per UL217, NFPA72, ISO8201

　　▪ Latching alarm indicator identifies alarm-initiating devices

　　图1。A5303典型应用电路