Freescale Semiconductor
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Document Number: MC14568
Rev. 1.0, 11/2006
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
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
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
GUARD 2
DETECT INPUT
GUARD 1
SENSITIVITY SET
OSCILLATOR CAP
HORN 2
HORN 1
VSS
ORDERING INFORMATION
Device
PC14568P/R2
648-08
PC14568ED/R2
Plastic Dip
Case No.
Package
FEEDBACK
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.
FEEDBACK
8
6
VDD
I/O
2
V
DD
11
HORN 2
10
HORN 1
LOW-V SET.
3
–
+
LOGIC
5
LED
V
DD
Power On
Reset
TIMING RES.
7
SENSITIVITY SET.
13
+
–
+
–
–Supply
9
V
DD
VSS
13
15
16
Oscillator
& Timing
OSC CAP.
12
4
(
)
1
TIMER
OUT
TIMER
START
Figure 2. Functional Block Diagram
Table 1. Maximum Ratings
Rating
Supply Voltage Range
Input Voltage Range
Maximum Current (Source/Sink) by Pins 6 (VDD) and Pin 9 (VSS)
Maximum Current Input Pins
Maximum Current Output Pins (Pins 2, 4, 5, 10, 11)
Maximum Current (Pin 15)
Operating Temperature Range
Storage Temperature Range
Human Body Model ESD Rating
Symbol
V
DD
V
IN
I
DS
I
IN
—
—
T
A
T
STG
V
ESD
Value
-0.5
to +15
-0.3
to V
DD
+0.3
30
±10
±25
±1.0
0 to +50
-55
to +125
1000
Unit
V
V
mA
mA
mA
mA
°C
°C
V
CAUTION: CMOS devices have input static protection but are susceptible to damage when exposed to extremely high static electrical charges.
MC14568
2
Sensors
Freescale Semiconductor
Table 2. Electrical Characteristics
Characteristics noted under conditions T
A
= +25°C, V
DD
= 9.0 V, V
SS
= 0 V, C
12
= 0.1
µF
(Oscillator Pin) R7 = 8.2 mΩf/fn (timing
resistor pin) unless otherwise noted.
Symbol
V
DD
I
IN
V
OS
Characteristic
Supply Voltage Range
Detector Input Current
Input Offset Voltage
Test Condition
Operating
0 to 40% RH,
V
IN
= 0 to 9.0 V
Active Guard
Active Guard
Detect Comparator
No Alarm to Alarm
Guard Amplifier
Smoke Comparator
To V
CC
To V
CC
No Alarm
Alarm
Test
Pin
6
15
14 – 15
16 – 15
15 – 13
13
14 – 15
13 – 15
14
16
12
4
After Pin 1 High to Low,
No Smoke
T
A
= 0 to 50°C
V
13
/V
DD
, Pin 3 Open Circuit
Pin 3 Open Circuit
I
OUT
= 16 mA, V
DD
= 9.0 V
I
OUT
= 16 mA, V
DD
= 7.2 V
I
OUT
= -16 mA, V
DD
= 9.0 V
I
OUT
= -16 mA, V
DD
= 7.2 V
Alarm
Low Battery
Alarm
Alarm
Low Battery
V
IH
V
IL
V
IH
V
IL
V
IN
= 9.0 V
V
OUT
= 0.5 V
V
DD
= 7.2 V, V
OUT
= 1.0 V
No Local Alarm, Not Latched
No Alarm, Standby
No Alarm, Timer Mode
4
6
13
3
10 – 11
Min
6.0
—
—
—
—
80
0.5
0.5
—
—
1.34
32
8.0
—
7.2
48.5
60.6
—
—
8.5
6.3
450
8.0
450
1350
32
6.3
—
4.5
—
20
500
10
8.0
32
8.0
Typ
9.0
—
—
—
—
130
—
—
10
500
1.67
40
10
6.43
—
50
63
0.1
—
8.8
—
500
10
500
1500
40
—
—
—
—
—
—
—
10
40
10
Max
12
1.0
100
100
50
160
V
DD
– 2.0
V
DD
– 2.0
—
—
2.0
48
12
10
7.8
51.5
65.6
0.5
0.9
—
—
550
12
550
1650
48
—
2.7
—
2.5
80
—
—
12
48
12
Unit
V
pA
mV
V
HYS
V
CM
LO-Z
HI-Z
t
CL
Hysteresis
Common Mode Range
Active Guard Impedance
Oscillator Period
Timer Out Pulse Width
Timer Period
mV
V
kΩ
s
ms
ms
min
V
%
%
V
V
TH
Low Voltage Threshold
Sensitivity Adj. Voltage
Low Battery Threshold
Horn Output Voltage
PW
ON
PW
OFF
Horn Output ON Time
Horn Output OFF Time
10 – 11
10 – 11
ms
ms
Feedback
Timer Start Logic Levels
Timer Start Input Current
Timer Out Output Current
I
LON
t
LON
t
LOFF
LED Output ON Current
LED Output ON Time
LED Output OFF Time
8
1
1
4
5
5
5
V
V
µA
µA
mA
ms
s
MC14568
Sensors
Freescale Semiconductor
3
Table 2. Electrical Characteristics (continued)
Characteristics noted under conditions T
A
= +25°C, V
DD
= 9.0 V, V
SS
= 0 V, C
12
= 0.1
µF
(Oscillator Pin) R7 = 8.2 mΩf/fn (timing
resistor pin) unless otherwise noted.
Symbol
I
I/O
I/O Current
(1)
Characteristic
V
I/O
= V
DD
- 2.0 V
V
I/O
= V
DD
- 2.0 V
V
I/O
= 1.0 V
Test Condition
No Alarm
Alarm
Charge Dump
After Local Alarm or Test
Alarm Out
V
IH
, V
DD
= 9.0 V
V
IL
, V
DD
= 9.0 V
V
DD
= 9.0 V
V
DD
= 12 V
No Alarm, No Loads
No Alarm, No Loads
Test
Pin
2
Min
25
-75
5.0
1.33
—
3.2
—
—
—
Typ
—
—
—
1.66
3.0
—
—
5.0
—
Max
60
—
—
1.99
—
—
1.5
9.0
12
Unit
µA
mA
mA
s
s
V
µA
I/O Charge Dump Duration
I/O Delay
V
I/O
I
DD
I/O V
IH
, V
IL
Supply Current
2
2
2
6
1. This specification also shows V
OH
of V
DD
- 2.0 V and V
OL
of 1.0 V at respective currents.
2. Negative current is defined as coming out of (sourcing) the specified device pin.
3. Alarm (Smoke) Condition is defined as V
15
< V
13
; No Alarm (No Smoke) Condition as V
15
> V
13
.
4 No Loads means the IC in standby mode with a 0.1
µF
capacitor on pin 12 to VSS and an 8.2 MΩ resistor on pin 7 to VDD with Pin 2 tied
low (LED and Horn are off).
PIN DESCRIPTIONS
TIMER START (PIN 1)
An internal timer is provided that can be used in various
configurations to allow for a period of reduced smoke
detector sensitivity (“hush”). When a high-to-low transition
occurs at pin 1, the internal timer is reset, the timer mode
enabled, and the circuit reset to a no alarm condition.
I/O (PIN 2)
Pin 2 is an input/output pin designed to be connected to
other smoke units for remote smoke sensing. In a local
smoke condition, this pin is driven high by the unit sensing
smoke. All other units in the network will then go into remote
smoke mode.
LOW-V SET (PIN 3)
Pin 3 is the low voltage set pin. This pin has an internal
fixed bias to monitor the battery. Using an external resistor
from pin 3 to either VDD or VSS allows the user to change
this bias to some fraction of V
DD
.
TIMER OUTPUT (PIN 4)
This pin is an open drain output that can be used in various
timer configurations to alter the IC’s sensitivity. A high to low
transition on pin 1 causes this output to pulse for 231 internal
clock cycles.
LED (PIN 5)
This pin is the LED cathode connection pin and is driven
low when the LED pulses.
VDD (PIN 6)
This is the positive power supply for the entire IC.
TIMING RESISTOR (PIN 7)
This pin, when tied through a resistor to VDD, works along
with pin 12 to set the bias current that controls the oscillation
frequency.
MC14568
4
Sensors
Freescale Semiconductor
FEEDBACK (PIN 8)
This is the feedback pin used for driving the piezo electric
element.
VSS (PIN 9)
This is the negative power supply pin for the entire IC
(usually ground).
HORN 1 (PIN 10)
This is one of two pins that drive the horn element (i.e.,
brass and silver).
HORN 2 (PIN 11)
This is one of two pins that drive the horn element (i.e.,
brass and silver).
OSCILLATOR CAP (PIN 12)
This pin, when tied to a low leakage capacitor to VSS,
works with pin 7 to set the internal oscillation frequency.
SENSITIVITY SET (PIN 13)
This pin is set internally to provide the reference sensitivity
for the detect pin (pin 15).
An external resistor from pin 13 to either VDD or VSS can
adjust the sensitivity.
GUARD 1/LOW Z (PIN 14)
This pin provides a low impedance guard for the detect pin
(pin 15) to reduce leakage currents.
DETECT INPUT PIN (PIN 15)
This pin functions as a low leakage smoke detect pin when
used in conjunction with an Ionization type element.
GUARD 2/HIGH Z (PIN 16)
This pin provides a high impedance guard for the detect
pin (pin 15) to reduce leakage currents.
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 V
DD
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.
MC14568
Sensors
Freescale Semiconductor
5
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