A5354CA ALLEGRO [Allegro MicroSystems], A5354CA Datasheet - Page 4

• Manufacturer Part Number: A5354CA
• Description: SMOKE DETECTOR WITH INTERCONNECT
• Manufacturer: ALLEGRO [Allegro MicroSystems]

NOTE 1: Negative current is defined as coming out of (sourcing) the specified device pin.
NOTE 2: Alarm (Smoke) Condition is defined as V
The A5354CA is a low-current CMOS circuit
providing all of the required features for an
ionization-type smoke detector.
Oscillator. An internal oscillator operates
with a period of 1.67 seconds during no-
smoke conditions. Every 1.67 seconds,
internal power is applied to the entire circuit
and a check is made for smoke. Every 24
clock cycles (40 seconds), the LED is pulsed
and a check is made for low battery by
comparing V
Because very-low currents are used in the
device, the oscillator capacitor at pin 12
should be a low-leakage type (PTFE, polysty-
rene, or polypropylene).
Detector Circuitry. When smoke is de-
tected, the resistor divider network that sets
the sensitivity (smoke trip point) is altered to
increase the sensitivity set voltage (pin 13)
by typically 130 mV with no external connec-
tions to pins 3 or 13. This provides hyster-
esis and reduces false triggering. An active
guard is provided on both pins adjacent to
the detector input (pin 15). The voltage at
pins 14 and 16 will be within 100 mV of the
ELECTRICAL CHARACTERISTICS continued
5354
SMOKE DETECTOR
with INTERCONNECT
Characteristic
I/O Current
I/O Alarm Voltage
I/O Delay
Supply Current
DD
to an internal reference.
Test
Pin
15
2
2
2
6
< V
CIRCUIT DESCRIPTION
13
; No Alarm (No Smoke) Condition as V
input. 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 amplifier is not power strobed
and thus provides constant protection from surface leakage currents.
The detector input has internal diode protection against static damage.
Alarm Circuitry. If smoke is detected, the oscillator period changes to
40 ms and the horn is enabled. The horn output is typically 160 ms
ON, 80 ms OFF. During the OFF time, smoke is again checked and
will inhibit further alarm output if smoke is not sensed. During smoke
conditions the low battery alarm is inhibited and the LED is driven at a
1 Hz rate.
Sensitivity Adjust. The detector sensitivity to smoke is set internally
by a voltage divider connected between V
can be externally adjusted to the individual characteristics of the
ionization chamber by connecting a resistor between pin 13 and V
between pin 13 and V
Low Battery. The low battery threshold is set internally by a voltage
divider connected between V
creased by connecting a resistor between pin 3 and V
old can be decreased by connecting a resistor between pin 3 and V
The battery voltage level is checked every 40 seconds during the 10
mA, 10 ms LED pulse. If an LED is not used, it should be replaced
with an equivalent resistor (typically 500
battery loading remains at 10 mA.
No Alarm, V
Alarm, V
External “Alarm” In
“Alarm” Out
V
V
DD
DD
= 12 V, No Alarm, No Loads
= 9.0 V, No Alarm, No Loads
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]
I/O
Test Conditions
= V
I/O
= V
DD
- 2.0 V
DD
SS
- 2.0 V
.
DD
15
> V
and V
13
.
SS
Min.
-7.5
3.0
25
—
—
. The threshold can be in-
—
DD
to 1000
and V
Typ.
3.0
5.0
—
—
—
—
SS
Limits
. The sensitivity
) such that the
DD
. The thresh-
Max.
9.0
60
12
—
—
—
Units
DD
mA
V
s
SS
A
A
A
, or
.