Datenblatt-Suchmaschine für elektronische Bauteile |
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MC145017 Datenblatt(PDF) 4 Page - Freescale Semiconductor, Inc |
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MC145017 Datenblatt(HTML) 4 Page - Freescale Semiconductor, Inc |
4 / 10 page Sensors 4 Freescale Semiconductor MC145017 Figure 3. Typical LED Output I–V Characteristic Figure 4. Typical Comparator Output I–V Characteristic Figure 5. Typical P Horn Driver Output I–V Characteristic DEVICE OPERATION Timing The internal oscillator of the MC145017 operates with a period of 1.65 seconds during no-smoke conditions. Each 1.65 seconds, internal power is applied to the entire IC and a check is made for smoke, except during LED pulse, Low Battery Alarm Chirp, or Horn Modulation (in smoke). Every 24 clock cycles a check is made for low battery by comparing VDD to an internal zener voltage. Since very small currents are used in the oscillator, the oscillator capacitor should be of a low leakage type. Detect Circuitry If smoke is detected, the oscillator period becomes 41.67 ms and the piezoelectric horn oscillator circuit is enabled. The horn output is modulated 500 ms on, 500 ms off. During the off time, smoke is again checked and will inhibit further horn output if no smoke is sensed. During smoke conditions the low battery alarm is inhibited, but the LED pulses at a 1.0 Hz rate. An active guard is provided on both pins adjacent to the detect input. The voltage at these pins will be within 100 mV of the input signal. 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 op amp is not power strobed and thus gives constant protection from surface leakage currents. Pin 15 (the Detect input) has internal diode protection against static damage. Sensitivity/Low Battery Thresholds Both the sensitivity threshold and the low battery voltage levels are set internally by a common voltage divider (please see Figure 2) connected between VDD and VSS. These voltages can be altered by external resistors connected from pins 3 or 13 to either VDD or VSS. There will be a slight interaction here due to the common voltage divider network. The sensitivity threshold can also be set by adjusting the smoke chamber ionization source. Test Mode Since the internal op amps and comparators are power strobed, adjustments for sensitivity or low battery level could be difficult and/or time-consuming. By forcing Pin 12 to VSS, the power strobing is bypassed and the outputs, Pins 1 and 4, constantly show smoke/no smoke and good battery/low 0 1 2 3 4 5 678 9 10 0.1 1.0 10.0 100.0 VDS, Drain To Source Voltage (Vdc) 01 2 3 4 5 6 7 8 9 10 0.01 0.1 1.0 10.0 VDS, Drain To Source Voltage (Vdc) VDD = 9.0 Vdc VDD = 7.2 Vdc TA = 25°C VDD = 9.0 Vdc or 7.2 Vdc TA = 25°C P-CH Source And N-CH Sink Current 0 1 2 3 4 5 678 9 10 1.0 10.0 100.0 1000.0 VDS, Drain To Source Voltage (Vdc) VDD = 9.0 Vdc TA = 25°C VDD = 7.2 Vdc P-CH Source Current 0 1 2 3 4 5 678 9 10 1.0 10.0 100.0 1000.0 VDS, Drain To Source Voltage (Vdc) VDD = 9.0 Vdc VDD = 7.2 Vdc TA = 25°C N-CH Sink Current |
Ähnliche Teilenummer - MC145017_07 |
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Ähnliche Beschreibung - MC145017_07 |
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