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MCZ146010EG Scheda tecnica(PDF) 10 Page - Freescale Semiconductor, Inc |
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MCZ146010EG Scheda tecnica(HTML) 10 Page - Freescale Semiconductor, Inc |
10 / 18 page Sensors 10 Freescale Semiconductor MC146010 The load for the low-supply test is non-coincident with the smoke tests, chamber sensitivity test, pushbutton test, or any alarm signals. The LED also provides a visual indication of the detector status as follows, assuming the component values shown in Figure 4: Standby (includes low-supply and chamber sensitivity tests) — Pulses every 32.4 seconds. Local Smoke — Pulses every 2.0 seconds (typical) Mute — Pulses every 2.0 seconds (typical) Remote Smoke — No Pulses Pushbutton test — Pulses every 2.0 seconds OSC (PIN 12) This pin is used in conjunction with external resistor R2 (7.5 M Ω) to V DD and external capacitor C3 (1500 pF) to VDD to form an oscillator with a nominal period of 7.9 msec (typical). R1 (PIN 13) This pin is use din conjunction with resistor R1(100 k Ω) to pin 12 and C3 (1500 pF, see pin 12 description) to determine the IRED pulse width. With this RC combination, the nominal pulse width is 105 µs. VSS (PIN 14) This pin is the negative supply potential and the return for the I/O pin. Pin 14 is usually tied to Ground. LOW-SUPPLY TRIP (PIN 15) This pin is connected to an external voltage which determines the low-supply alarm threshold. The trip voltage is obtained through a resistor divider connected between the VDD and LED pins. The low-supply alarm threshold voltage (in volts) = (5R7/R6)+5 where R6 and R7 are in the same units. TEST/MUTE (PIN 16) This input has an on-chip pull-down device and is used to manually invoke a test mode, a mute mode, or a calibration mode. The Pushbutton Test mode is initiated by a high level at Pin 16 (usually a depression of a S.P.S.T. normally-open pushbutton switch to VDD). After one oscillator cycle, the IRED pulses approximately every 1.0 second, regardless of the presence of smoke. Additionally, the amplifier gain is increased by automatic selection of C1. Therefore the background reflections in the smoke chamber may be interpreted as smoke, generating a simulated smoke condition. After the second IRED pulse, a successful test activates the horn-driver and I/O circuits. The active I/O allows remote signaling for a system testing. When the Pushbutton Test switch is released, the Test input returns to VSS due to the on-chip pull-down device. After one oscillator cycle, the amplifier gain returns to normal, thereby removing the simulated smoke condition. After two additional IRED pulses, less than three seconds, the IC exits the alarm mode and returns to standby timing. The Pushbutton Test will also activate the Alarm Memory feature. If there was a previous alarm detected by the unit, the horn will chirp every ¼ second as long as the Test Button is pressed. Upon releasing of the Test Button, Alarm memory will be reset. Subsequent pressing of the Test Button will result in a Pushbutton Test for simulated smoke. Pressing the Test Button while in the MUTE mode will result in resetting of MUTE (and additionally a normal Pushbutton Test). The MUTE mode (IMF) is initiated by a mid level voltage (around ½ VDD) at pin 16. A parallel Mute Button to an existing Test Button needs to be installed at the test pin. A smoke condition must be present for the MUTE mode to be activated. If a no smoke condition gets detected while in the MUTE mode, the IMF 8 minute window gets reset. The unit will return to Standby mode. Once in the MUTE mode, the audible smoke alarm (horn) is temporarily disabled for approximately 8 minutes while smoke condition is being detected. A visual smoke alarm will remain (LED flashing) during MUTE mode. A high smoke voltage reference will also be activated at this time. Simultaneous smoke and high smoke sampling will allow the unit to enable the horn driver in case a high smoke condition occurs during MUTE where the high smoke threshold is crossed. The MUTE mode can be overridden by the following conditions: 1) a no smoke condition is detected, 2) high smoke level detected, 3) remote smoke detected through I/O, 4) reset through test Button, 5) timeout of 8 minute window. To help prevent a jammed Mute Button condition, the divider string on the Mute Button should include a resistor to VDD, R15 (around 10 M Ω) and a resistor R16 (4.7 MΩ) and capacitor, C7 (0.047 mF) in series to VSS. CALIBRATION To facilitate checking the sensitivity and calibrating smoke detectors, the MC146010 can be placed in Calibration mode. In this mode, certain device pins are controlled/reconfigured as shown in Table 4. To place the part in Calibration mode, Pin 16 (Test/ Mute) must be pulled below VSS pin with 100 µA continuously drawn out of the pin for at least one cycle of the OSC pin. To exit this mode, the Test/ Mute pin is floated for at least one OSC cycle. In the Calibration mode, the IRED pulse rate is increased. An IRED pulse occurs every clock cycle. Also, Strobe is always Active Low. It is recommended to short R12 (Figure 5) in this mode. This will allow for a similar recovery of the emitter circuitry as in normal operation. Pin 1, pin 2, and pin 12 should be buffered with a unity gain amplifier to measure their outputs. |
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