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A5303 Datasheet(PDF) 6 Page - Allegro MicroSystems |
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A5303 Datasheet(HTML) 6 Page - Allegro MicroSystems |
6 / 14 page Photoelectric Smoke Detector with Interconnect, Timer, and Latching Alarm Indicator A5303 6 Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com Pin and Circuit Description (In Typical Application) C1 Pin A capacitor connected to this pin determines the gain of the photoamplifier, Ae , during the push-to-test mode and during the chamber monitor test. A typical capacitor value for this high- gain (supervisory) mode is 0.047 μF, but it should be selected based on the photochamber background reflections reaching the detector and the required level of sensitivity. Ae = 1 + (C1/ 12), where C1 is in pF. Ae should not exceed 10,000 and thus C1 should not exceed 0.1 μF. Coupling of other signals to the C1, C2, and DETECT inputs must be minimized. C2 Pin A capacitor connected to this pin determines the gain of the photoamplifier, Ae, during standby. A typical capacitor value for this low-gain mode is 4700 pF, but it should be selected based on a specific photochamber and the desired level of sensitiv- ity to smoke. Ae = 1 + (C2/ 12), where C2 is in pF. Ae should not exceed 10,000 and thus C2 should not exceed 0.1 μF. This gain increases by a nominal 45% after a local alarm is detected (three consecutive detections). A resistor must be installed in series with the C2 capacitor. DETECT Pin This is the input to the photoamplifier and is connected to the cathode of the photodiode. The photodiode is operated at zero bias and should have low dark leakage current and low capaci- tance. A shunt resistor must be installed in parallel with the photodiode. STROBE Pin This output provides a strobed, regulated voltage of VDD – 2 V. The minus side of all internal and external photoamplifier cir- cuitry is referenced to this pin. VDD Pin This pin is connected to the positive supply potential, typically 3 V. LVSET Pin This pin allows the user to externally adjust the low-battery alarm threshold. To increase the threshold, a resistor can be con- nected between LVSET and VDD. To decrease the threshold, a resistor can be connected between LVSET and VSS. IRED Pin This output provides a pulsed drive current for the external IR emitter. To minimize noise impact, the IRED is not active when the visible LED output is active. ISET Pin This pin allows the user to externally set the IRED current by connecting a resistor between it and VSS. The IRED current controls the amount of light generated by the IR LED in the chamber. The IRED current, in mA, can be approximated using the following equation: IIRED (mA) = 300 / RISET (1) The chosen resistor should set a maximum of 300 mA (typically a minimum of 1Ω). I/O Pin A connection at this pin allows multiple smoke detectors to be interconnected. If any single unit detects smoke, its I/O pin is driven high, and all connected units will sound their associated alarm indicators. As an input, this pin is sampled every 4 clock cycles (nominally 43 ms) during standby, and two consecutive samples and one additional clock with I/O high are required before signaling an alarm. If the I/O line goes low at all during the 96.8 ms, the remote alarm is not enabled, providing sig- nificant immunity to I/O noise and other pulses on the I/O line which are shorter than 9 clock cycles. The LED is suppressed when an alarm is signaled from an interconnected unit, and any local-alarm condition causes this pin to be ignored as an input. An internal NMOS device acts as a charge dump to aid in applications involving a large (distributed) capacitance, and is activated at the end of a local or test alarm. This pin has an on-chip pull-down device and must be left unconnected if not used. In the application, there should be a series current-limiting resistor to other smoke alarms. SOUT0, SOUT1, SOUT2 Pins These pins provide push-pull CMOS logic outputs to control an external sound IC. The outputs indicate the state of the device as follows: Condition SOUT2 SOUT1 SOUT0 Standby L L L Local Alarm L L H Remote Alarm L H L Push-Test Passed L H H Push-Test Failed H L L Low-Battery H L H Degraded Chamber H H L |
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