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Freescale Semiconductor Technical Data
Document Number: MC14468 Rev 5.0, 11/2006
Low-Power CMOS Ionization Smoke Detector IC with Interconnect
The MC14468, 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. Features * * * * * * * * * * * * * Ionization Type with On-Chip FET Input Comparator Piezoelectric Horn Driver Guard Outputs on Both Sides of Detect Input Input-Production Diodes on the Detect Input Low-Battery Trip Point, Internally Set, can be Altered Via External Resistor Detect Threshold, Internally Set, can be Altered Via External Resistor Pulse Testing for Low Battery Uses LED for Battery Loading Comparator Output for Detect Internal Reverse Battery Protection Strobe Output for External Trim Resistors I/O Pin Allows Up to 40 Units to be Connected for Common Signaling Power-On Reset Prevents False Alarms on Battery Change Pb-Free Packaging Designated by Suffix Code ED
MC14468
LOW-POWER CMOS IONIZATION SMOKE DETECTOR IC WITH INTERCONNECT
P SUFFIX ED SUFFIX (PB-FREE) 16-LEAD PLASTIC DIP CASE 648-08
DETECT COMP. OUT I/O LOW V SET
1 2 3 4 5 6 7 8
16 15 14 13 12 11 10 9
GUARD HI-Z DETECT INPUT GUARD LO-Z SENSITIVITY SET OSC CAPACITOR SILVER BRASS VSS
ORDERING INFORMATION
Device MC14468P -10 to 60C MC14468ED 648-08 Plastic Dip Temperature Range Case No. Package
STROBE OUT LED VDD TIMING RESISTOR FEEDBACK
Figure 1. Pin Connections
(c) Freescale Semiconductor, Inc., 2006. All rights reserved.
To Other Units
VDD
VDD
I/O 2
FEEDBACK 8
45 K Low-Battery Comparator LOW V SET 1 DETECT COMPARATOR OUT 280 K 13 3 11 SILVER
- +
Alarm Logic Detect Comparator 10 BRASS
+ -
15 DETECT INPUT LO-Z 14 VDD
Power-On Reset
325 K
STROBE OUT
4
Guard Amp
HI-Z 16
OSC and Timing
5
LED
+ -
VDD = Pin 6 VSS = Pin 9 12 7 VDD
Figure 2. Block Diagram Table 1. Maximum Ratings(1) (Voltages referenced to VSS)
Rating DC Supply Voltage Input Voltage, All Inputs Except Pin 8 DC Current Drain per Input Pin, Except Pin 15 = 1 mA DC Current Drain per Output Pin Operating Temperature Range Storage Temperature Range Reverse Battery Time Symbol VDD VIN I I TA TSTG tRB Value -0.5 to +15 -0.25 to VDD + 0.25 10 30 -10 to +60 -55 to +125 5.0 Unit V V mA mA C C s
1. Maximum Ratings are those values beyond which damage to the device may occur. This device contains circuitry to protect the inputs against damage due to high static voltages or electric fields; however, it is advised normal precautions be taken to avoid application of any voltage higher than maximum rated voltages to this high impedance circuit. For proper operation it is recommended VIN and VOUT be constrained to the range VSS (VIN or VOUT) VDD.
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Table 2. Recommended Operating Conditions (Voltages Referenced to VSS)
Parameter Supply Voltage Timing Capacitor Timing Resistor Battery Load (Resistor or LED) Symbol VDD -- -- -- Value 9.0 0.1 8.2 10 Unit V F M mA
Table 3. Electrical Characteristics (TA = 25C)
Characteristic Operating Voltage Output Voltage Piezoelectric Horn Drivers (IOH = -16 mA) Comparators (IOH = -30 A) Piezoelectric Horn Drivers (IOL = +16 mA) Comparators (IOL = +30 A) Output Voltage -- LED Driver, IOL = 10 mA Output Impedance, Active Guard Pin 14 Pin 16 Operating Current (RBIAS = 8.2 M) Input Current -- Detect (40% R.H.) Input Current, Pin 8 Input Current @ 50C, Pin 15 Internal Set Voltage Low Battery Sensitivity Hysteresis Offset Voltage (Measured at VIN = VDD/2) Active Guard Detect Comparator Input Voltage Range, Pin 8 Input Capacitance Common Mode Voltage Range, Pin 15 I/O Current, Pin 2 Input, VIH = VDD -2 Output, VOH = VDD -2 Symbol VDD VOH 7.2 9.0 7.2 9.0 7.2 9.0 9.0 9.0 12.0 9.0 9.0 -- 9.0 -- 9.0 9.0 9.0 VIN CIN VCM IIH IOH -- -- -- -- -- 6.3 8.5 -- -- -- -- -- -- -- -- -- -- 7.2 47 75 -- -- VSS - 10 -- 0.6 25 -4.0 -- 8.8 -- 0.1 -- -- -- 5.0 -- -- -- -- -- 50 100 -- -- -- 5.0 -- -- -- -- -- 0.9 0.5 3.0 10 1000 9.0 12.0 1.0 0.1 6.0 7.8 53 150 100 50 VDD + 10 -- VDD - 2 100 -16 V pF V A mA A pA A pA V %VDD mV mV VDD VDC -- Min 6.0 Type(1) -- Max 12 Unit V V
VOL VOL LO-Z HI-Z IDD IIN IIN IIN VLOW VSET VHYS VOS
V V k
1. Data labelled "Typ'' is not to be used for design purposes, but is intended as an indication of the IC's potential performance.
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Table 4. Timing Parameters (C = 0.1 F, Rbias = 8.2 M, VDD = 9.0 V, TA = 25C, See Figure 7)
Characteristics Oscillator Period Oscillator Rise Time Horn Output (During Smoke) LED Output Horn Output (During Low Battery) On Time Off Time Between Pulses On time On Time Between Pulses No Smoke Smoke Symbol tCI tR PWON PWOFF tLED PWON tON tOFF Min 1.34 32 8.0 120 60 32 8.0 8.0 32 Typ(1) 1.67 40 10 160 80 40 10 10 40 Max 20 48 12 208 104 48 12 12 48 Units s ms ms ms ms s ms ms s
1. Data labelled "Typ'' is not to be used for design purposes, but is intended as an indication of the IC's potential performance.
100.0 VDD = 9.0 Vdc ID, Drain Current (mA) TA = 25C
10.0 TA = 25C VDD = 9.0 Vdc or 7.2 Vdc
10.0 VDD = 7.2 Vdc
ID, Drain current (mA)
1.0
1.0
0.1 P-CH Source and N-CH Sink Current 0.01 0 1 2 3 4 5 6 7 VDS, Drain To Source Voltage (Vdc) 8 9 10
0.1 0
1
2
3
4
5
6
7
8
9
10
VDS, Drain To Source Voltage (Vdc)
Figure 3. Typical LED Output I-V Characteristic
Figure 4. Typical Comparator Output I-V Characteristic
1000.0 TA = 25C ID, Drain current (mA) 100.0
1000.0 TA = 25C VDD = 9.0 Vdc ID, Drain current (mA) 100.0
VDD = 9.0 Vdc
10.0
VDD = 7.2 Vdc
VDD = 7.2 Vdc 10.0 N-CH Sink Current
P-CH Source Current 1.0 0 1 2 3 4 5 6 7 8 9 10 1.0 0 1 2 3 4 5 6
7
8
9
10
VDS, Drain To Source Voltage (Vdc)
VDS, Drain To Source Voltage (Vdc)
Figure 5. Typical P Horn Driver Output I-V Characteristic
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DEVICE OPERATION
Timing The internal oscillator of the MC14468 operates with a period of 1.67 seconds during no-smoke conditions. Each 1.67 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 40 ms and the piezoelectric horn oscillator circuit is enabled. The horn output is modulated 160 ms on, 80 ms off. During the off time, smoke is again checked and will inhibit further horn output if no smoke is sensed. During local smoke conditions the low battery alarm is inhibited, but the LED pulses at a 1.0 Hz rate. In remote smoke, the LED is inhibited as well. 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. Interconnect The I/O (Pin 2), in combination with VSS, is used to interconnect up to 40 remote units for common signaling. A Local Smoke condition activates a current limited output driver, thereby signaling Remote Smoke to interconnected units. A small current sink improves noise immunity during non-smoke conditions. Remote units at lower voltages do not draw excessive current from a sending unit at a higher voltage. The I/O is disabled for three oscillator cycles after power up, to eliminate false alarming of remote units when the battery is changed. 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 output, Pin 1, constantly shows smoke/no smoke. Pin 1 = VDD for smoke. In this mode and during the 10 ms power strobe, chip current rises to approximately 50 A. LED Pulse The 9-volt battery level is checked every 40 seconds during the LED pulse. The battery is loaded via a 10 mA pulse for 10 ms. If the LED is not used, it should be replaced with an equivalent resistor such that the battery loading remains at 10 mA. Hysteresis When smoke is detected, the resistor/divider network that sets sensitivity is altered to increase sensitivity. This yields approximately 100 mV of hysteresis and reduces false triggering.
1M 1 To Other Units 2 3 4 330 5 6 7 8.2 M 0.1 F + 9V 1.5 M* 0.001 F 8 16 15 14 13 12 11 10 9 0.1 F
1M
Test
MC14468
*Note: Component values may change depending on type of piezoelectric horn used. 220 k*
Figure 6. Typical Application as Ionization Smoke Detector MC14468 Sensors Freescale Semiconductor 5
Standby No Smoke/ No Low Battery Smoke/No Low Battery OSCILLATOR (Pin 12) DETECT OUT (Pin 1) LOW BATTERY (Internal) HYSTERESIS (Internal) (Pin 13) (Pin 14) SAMPLE (Internal) Smoke Low = Disable HORN High = Enable (Pin 10 and 11) LED (Pin 5) 24 Clock Cycles STROBE OUT (Pin 14) I/O (Pin 2) Output (Local) I/O (Pin 2) Input (Remote) LED (40S) Battery Test
Smoke/Low Battery
40 ms 10 ms
No Smoke/Low Battery
1.67 s
(Note 1) Suppressed Chirp (Note 3) 24 Clock Cycles (0.96 s) 24 Clock Cycles (Note 3) 6 Clock Cycles (10.0 s)
Note: Horn Modulation Not Self-Completing
(Suppressed LED for Remote Only)
Notes: 1. Horn modulation is self-completing. When going from smoke to no smoke, the alarm condition will terminate only when horn is off. 2. Comparators are strobed on once per clock cycle (1.67 s for no smoke, 40 ms for smoke). 3. Low battery comparator information is latched only during LED pulse. 4. ~ 100 mV p-p swing.
Figure 7. Timing Diagram
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PACKAGE DIMENSIONS
CASE 648-08 ISSUE T 16-LEAD PLASTIC DIP
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REVISION HISTORY
REVISION 5.0
DATE 11/2006
DESCRIPTION OF CHANGES * * * Implemented Revision History page Converted to Freescale format Added part number MC14468ED to Ordering Information.
MC14468 8 Sensors Freescale Semiconductor
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MC14468 Rev. 5.0 11/2006

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