A5303: Photoelectric Smoke Detector with Interconnect, Timer, and Latching Alarm Indicator - ALLEGRO MICROSYSTEMS - #1

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Description 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 ìs 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. 5303-DS Features and Benefits 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 Photoelectric Smoke Detector with Interconnect, Timer, and Latching Alarm Indicator Package: 20-pin TSSOP (suffix LE) Not to scale A5303 Typical Application Diagram Control Logic SOUT0 VDD TEST C1 56 nF C2 5.6 nF DETECT Gain Select STROBE VDD IRED OSC Timing Low Batt 1.2 V 3 V 100 ìF LED VSS 560 Ù 200 kÙ 10 ìF VDD - 1.6 V OSCCAP 1500 pf Push-to-test HUSH Connect HUSH to VSS to disable timer mode Connect to allow timer (hush) mode operation ISET LVSET Low Batt Sample A A A resistor connected between this pin and VDD or VSS adjusts SOUT1 Voice IC outputs the low-battery threshold 100 kÙ 10 ÌÙ SOUT2 TRES I/O 220 Ù To / from other units VDD VDD VDD BLINK In standby, BLINK = VDD causes LED to blink, BLINK = VSS causes LED not to blink HORN Output to optional boost converter to drive a piezo horn Smoke Chamber Red LED B B R1 R2 5 k Ù 3 kÙ 3 Ù 1 k Ù