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PDF MC14568 Data sheet ( Hoja de datos )
| Número de pieza | MC14568 | |
| Descripción | Low-Power CMOS Ionization Smoke Detector | |
| Fabricantes | Freescale Semiconductor | |
| Logotipo |  |
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Low-Power CMOS Ionization Smoke
Detector with Interconnect and Timer
The MC14568, when used with an ionization chamber and a small number of
external components, will detect smoke. When smoke is sensed, an alarm is
sounded via an external piezoelectric transducer and internal drivers. This circuit
is designed to operate in smoke detector systems that comply with UL217 and
UL268 specifications.
An internal oscillator with associated logic controls the overall functionality by
powering down the device for 1.67 seconds and sensing smoke in a 10 ms
window. In this way, standby current consumption is reduced to between 5.0 and
9.0 µA, thus providing longer battery life. In addition, a networking capability
allows as many as 125 to be interconnected so that if any unit senses smoke, all
units will sound an alarm.
The MC14568 is supplied in a 16-pin dual in-line plastic package and is
designed to run on a power supply between 6 to 12 Volts.
Features
• Speed-Up Sampling Rate of 40 ms of Internal Clock Period (Pin 12) After First
Detection of Smoke
• Timer Function for Reduced Sensitivity for a Nominal Period of 6.43 Minutes
(10 Minutes Max)
• High-Smoke Detection in the “Reduced Sensitivity” Mode
• Internal and External Low Battery Threshold
• Internal and External Smoke Reference Settings
• Guaranteed Power Up Without Random LED and Horn Chirps
• Reversed Battery Protection
• Low Leakage Detect Pin
• Metal Option to Add Double Chirp at End of Reduced Sensitivity Period;
Default is No Chirp
• Pb-Free Packaging Designated by Suffix Code ED
Device
PC14568P/R2
PC14568ED/R2
ORDERING INFORMATION
Case No.
648-08
Package
Plastic Dip
Document Number: MC14568
Rev. 1.0, 11/2006
MC14568
LOW-POWER CMOS IONIZATION
SMOKE DETECTOR WITH
INTERCONNECT AND TIMER
P SUFFIX
ED SUFFIX (PB-FREE)
PLASTIC DIP
CASE 648-08
TIMER START
I/O
LOW-V SET
TIMER OUT
LED
VDD
TIMING R
FEEDBACK
1
2
3
4
5
6
7
8
16 GUARD 2
15 DETECT INPUT
14 GUARD 1
13 SENSITIVITY SET
12 OSCILLATOR CAP
11 HORN 2
10 HORN 1
9 VSS
Figure 1. Pin Connections
This document contains certain information on a new product.
Specifications and information herein are subject to change without notice.
© Freescale Semiconductor, Inc., 2006. All rights reserved.
1 page  
DEVICE OPERATION
In a NO SMOKE condition (i.e., standby mode with detect
pin 15 higher than internal reference pin 13), the oscillator
operates with a period of 1.67 s and the LED will flash once
every 24-clock periods (or every 40 s).
The smoke detect pin (pin 15) is connected to the
ionization chamber and leads to the inverting input of a
CMOS detect comparator. The voltage on this pin is
compared to an internal reference voltage on the non-
inverting input of the detect comparator set up by a resistor
divider network and a FET switch (this reference voltage can
be increased or decreased by an external resistor from pin 13
to VDD or VSS).
Periodically (every 1.67 s and for a 10 ms window) power
is supplied to the entire IC and a check is made for a SMOKE
condition. During this window the FET switch is turned on and
the detect pin voltage (pin 15) is compared to the internal
reference voltage (pin 13). If the detect pin is lower than the
reference this indicates a SMOKE condition.
A SMOKE condition speeds up the internal oscillator,
which now oscillates with an internal period of 40 ms (the
rising edge of the saw tooth periodic signal on pin 12 remains
the same while the falling edge falls faster in a SMOKE
condition).
Furthermore, a SMOKE condition causes the resistor
divider network that sets the smoke detect reference voltage
to change in such a way as to make the reference voltage
increase by approximately 130 mV (with no external
connections to pin 13 or to pin 3).
This provides hysteresis and reduces false triggering. This
hysteresis is turned off when the IC exits a SMOKE condition
and returns to standby mode.
Once in a SMOKE condition, the LED will flash every 24-
clock cycles (once every second). The horn (piezo electric
element) driver is activated during a smoke condition with a
typical ON/OFF time of 160 ms ON, 80 ms OFF.
During the off time, the IC re-checks to see if a SMOKE
condition still exists. If no smoke is detected the horn driver is
suppressed. During a SMOKE condition the low voltage
battery check is inhibited.
NO SMOKE AND LOW BATTERY CHECK
During a NO SMOKE condition (i.e., standby mode) the
LED is pulsed to load the battery every 24-clock cycles (every
40 seconds) and a fraction of the battery voltage (set
internally by a resistor divider network and pulsed “ON” by a
internal FET) is compared to an internal reference voltage set
by a reversed biased Zener diode by an internal CMOS
comparator. The fraction of the supply voltage (pin 3) to be
compared to the internal reference voltage for low battery
check can be raised or lowered by connecting an external
resistor between pin 3 and VDD or pin 3 and VSS. If low
battery is detected a warning “chirp” will be sounded by the
horn driver once every 24-clock cycles (a low battery
condition does NOT cause the oscillator to speed up as does
a SMOKE condition). Low battery check will still be performed
in reduced sensitivity mode and a low battery chirp will be
heard if VDD falls below specified value.
TIMER
An internal timer is provided that can be used in various
configurations to allow for a period of reduced smoke
detector sensitivity.
Sensors
Freescale Semiconductor
MC14568
5
5 Page 
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© Freescale Semiconductor, Inc. 2006. All rights reserved.
MC14568
Rev. 1.0
11/2006
11 Page | ||
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| PDF Descargar | [ Datasheet MC14568.PDF ] | |
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