A5303: Photoelectric Smoke Detector with Interconnect, Timer, and Latching Alarm Indicator

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 (LE) package (0.65 mm nominal lead pitch) and a 20-contact QFN (ES) package with exposed thermal pad. Both packages are lead (Pb) free with 100% matte tin leadframe plating.


Astrorep Inc. (Allegro and Sanken Semiconductors, Sanken Power Supplies)
141 John Street, Suite 300
Babylon, NY 11702
Phone: (631)422-2500
Fax: (631)422-2504
Web: www.astrorepinc.com
Email: donna.tweedy@astrorepinc.com

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  • 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

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Product Image Typical Application

Part Number Specifications and Availability

Part Number Package Type Temperature RoHS
Part Composition /
RoHS Data
Comments Samples Check
Distributor Stock
A5303SESTR-T 20-lead QFN -20°C to 85°C Yes View Data Contact your
local sales rep
Check Stock
A5303SLE-T 20-lead TSSOP -20°C to 85°C Yes View Data Contact your
local sales rep
Check Stock
A5303SLETR-T 20-lead TSSOP -20°C to 85°C Yes View Data Contact your
local sales rep
Check Stock

Allegro’s products are not to be used in any devices or systems, including but not limited to life support devices or systems, in which a failure of Allegro’s product can reasonably be expected to cause bodily harm.

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