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5364 Datasheet(PDF) 4 Page - Allegro MicroSystems |
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5364 Datasheet(HTML) 4 Page - Allegro MicroSystems |
4 / 8 page 5364 SMOKE DETECTOR WITH INTERCONNECT 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 I/O Current 2 No Alarm, VI/O = VDD - 2.0 V 25 — 60 µA Alarm, VI/O = VDD - 2.0 V -7.5 — — mA I/O Alarm Voltage 2 External “Alarm” In 3.0 — — V I/O Delay 2 “Alarm” Out — 3.0 — s Supply Current 6 VDD = 9.0 V, No Alarm, No Loads — 5.0 9.0 µA VDD = 12 V, No Alarm, No Loads — — 12 µA Test Limits Characteristic Pin Test Conditions Min. Typ. Max. Units ELECTRICAL CHARACTERISTICS (continued) CIRCUIT DESCRIPTION The A5364CA is a low-current CMOS circuit providing all of the required features for an ionization-type smoke detector. Oscillator. An internal oscillator operates with a period of 1.67 seconds during no- smoke conditions. Every 1.67 seconds, internal power is applied to the entire circuit and a check is made for smoke. Every 24 clock cycles (40 seconds), the LED is pulsed and a check is made for low battery by comparing V DD to an internal reference. Because very-low currents are used in the device, the oscillator capacitor at pin 12 should be a low-leakage type (PTFE, polysty- rene, or polypropylene). Detector Circuitry. When smoke is detected, the resistor divider network that sets the sensitivity (smoke trip point) is altered to increase the sensitivity set voltage (pin 13) by typically 130 mV with no external connec- tions to pins 3 or 13. This provides hysteresis and reduces false triggering. An active guard is provided on both pins adjacent to the detector input (pin 15). The voltage at pins 14 and 16 will be within 100 mV of the input. This will keep surface leakage currents to a minimum and provide a method of measuring the input voltage without loading the ionization chamber. The active guard amplifier is not power strobed and thus provides constant protection from surface leakage currents. The detector input has internal diode protection against static damage. Alarm Circuitry. If smoke is detected, the oscillator period changes to 40 ms and the horn is enabled. The horn output is typically 0.5 s ON, 0.5 s OFF, 0.5 s ON, 0.5 s OFF, 0.5 s ON, 1.5 s OFF (temporal horn pattern). During the OFF time, smoke is checked and will inhibit further alarm output if smoke is not sensed. During smoke conditions the low battery alarm is inhibited and the LED is driven at a 1 Hz rate. Sensitivity Adjust. The detector sensitivity to smoke is set inter- nally by a voltage divider connected between V DD and VSS. The sensitivity can be externally adjusted to the individual characteristics of the ionization chamber by connecting a resistor between pin 13 and V DD, or between pin 13 and VSS. Low Battery. The low battery threshold is set internally by a voltage divider connected between V DD and VSS. The threshold can be in- creased by connecting a resistor between pin 3 and V DD. The threshold can be decreased by connecting a resistor between pin 3 and V SS. The battery voltage level is checked every 40 seconds during the 10 mA, 10 ms LED pulse. If an LED is not used, it should be replaced with an equivalent resistor (typically 500 Ω to 1000 Ω) such that the battery loading remains at 10 mA. NOTE 1: Negative current is defined as coming out of (sourcing) the specified device pin. NOTE 2: Alarm (Smoke) Condition is defined as V 15 < V13; No Alarm (No Smoke) Condition as V15 > V13. |
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