Analog Integrated Circuit Device Data
4 Freescale Semiconductor
14600
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Archive Information
Archive Information
DEVICE OPERATION
Timing
The internal oscillator of the MC14600 operates with a
period of 1.65 seconds during no-alarm conditions. Each
1.65 seconds, internal power is applied to the entire IC and a
check is made for an alarm input level except during LED
pulse, Low Battery Alarm Chirp, or Horn Modulation (in
alarm). Every 24 clock cycles a check is made for low battery
by comparing V
DD
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 an alarm condition is detected, the oscillator period
becomes 41.67 ms and the piezoelectric horn oscillator
circuit is enabled. The horn output is modulated 167 ms on,
83
ms off. During the off time, alarm detect input (Pin 15) is
again checked and will inhibit further horn output if no alarm
condition is sensed. During alarm conditions the low battery
chirp is inhibited, and the LED pulses at a 1.0 Hz rate.
An active guard is provided on a pin adjacent to the detect
input (Pin 16). The voltage at this pin will be within 100 mV of
the input signal. Pin 16 will allow monitoring of the input signal
at pin 15 through a buffer. 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.
Low Battery Threshold
The low battery voltage level is set internally by a voltage
divider connected between VDD and VSS. This voltage can
be altered by external resistors connected from pin 3 to either
VDD or VSS. A resistor to VDD will decrease the threshold
while a resistor to GND will increase it.
Alarm Threshold (Sensitivity)
The alarm condition voltage level is set externally through
Pin 13. A voltage divider can be used to set the alarm trip
point. Pin 13 is connected internally to the negative input of
the detect comparator.
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 so that the battery loading remains
at 10
mA.
.
Figure 3. Typical Application Components
MC14600
116
2
3
4
5
6
7
8
15
14
13
12
11
10
9
330 Ω
R
BIAS
0.1 μF
1.5 MΩ*
0.001 μF
220 kΩ*
COSC
DETECT
INPUT
R1
VDD
VDD
VDD
R2
R
P
*Note: Component values may change depending on the type of piezoelectric horn used.
