MPXM2102AS datasheet(614/670 Pages) MOTOROLA

614 / 670 page

MC14600

4–22

Motorola Sensor Device Data

www.motorola.com/semiconductors

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 VDD to an internal zener voltage. Since very

small currents are used in the oscillator, the oscillator capaci-

tor 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 cir-

cuit 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 sig-

nal at pin 15 through a buffer. The active guard op amp is not

power strobed and thus gives constant protection from sur-

face 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 thresh-

old 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 dur-

ing 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 2. Typical Application Components

MC14600

116

330

Ω

Rbias

0.1

µF

1.5 M

Ω*

0.001

µF

220 k

Ω*

COSC

*NOTE: Component values may change depending on type of piezoelectric horn used.

DETECT

INPUT

VDD

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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