a5364 Allegro MicroSystems, Inc., a5364 Datasheet - Page 6

• Manufacturer Part Number: a5364
• Description: Ionization Smoke Detector With Interconnect
• Manufacturer: Allegro MicroSystems, Inc.

A5364
of the ionization chamber by connecting a resistor between the
SENSITIVITY SET pin and either the VDD or VSS pins.
With no external connections on the SENSITIVITY SET pin,
while the A5364 is checking for smoke:
To increase sensitivity, a resistor can be connected between
SENSITIVITY SET and VDD, with the value:
where
To decrease sensitivity, a resistor can be connected between
SENSITIVITY SET and VSS, with the value:
where
Low Battery
The low battery condition threshold is set internally by a voltage
divider connected between VDD and VSS. The threshold can
be externally adjusted by connecting a resistor between the
LOW-V SET pin and either the VDD or VSS pins.
To increase the threshold, a resistor can be connected between
LOW-V SET and VSS. Given an initial threshold, V
nally 7.5 V), and a target threshold, V
have the value:
where
To decrease the threshold, a resistor can be connected between
LOW-V SET and VDD. Given an initial threshold, V
R
R
R
LOWVSET
K = 1 / (V
K = 1 / (V
SENSITIVITYSET
SENSITIVITYSET
K = V
V
SENSITIVITYSET
= 600E3 × K / (1 – 0.375 × K) ,
DD
(th)set
DD
/ V
/ V
/ [0.727 × V
SENSITIVITYSET
= 1.1E6 × K / (1 – K) ,
= 1.1E6 × K / (1 – K) ,
SENSITIVITYSET
= V
(th)set
DD
(th)init
, the resistor should
/ 2 .
– 1 .
] – 1) .
– 1) .
(th)init
(th)init
(nomi-
(nomi-
nally 7.5 V), and a target threshold, V
have the value:
where
The battery voltage level is checked approximately every 40 sec-
onds during the (approximately) 10 mA, 10 ms LED pulse. If an
LED is not used, it should be replaced with an equivalent resistor
(typically 500 to 1000 Ω) such that the battery loading remains
about 10 mA.
I/O
A connection to the I/O pin allows multiple smoke detectors to
be interconnected. If any single unit detects smoke, its I/O pin is
driven high (after a nominal 3 s delay), and all connected units
will sound their associated horns. The LED is suppressed when
an alarm is signaled from an interconnected unit, and any local
alarm condition causes the I/O pin to be ignored as an input. This
pin has an on-chip pulldown device and must be left unconnected
if not used.
Testing
On power-up, all internal counters are reset. Internal test cir-
cuitry allows low battery check by holding the FEEDBACK and
OSC CAP pins low during power-up, then reducing V
monitoring the HORN1 pin. HORN1 will be driven high when
V
can be accelerated by driving the OSC CAP pin with a 2 kHz
square wave. The 10 ms strobe period must be maintained for
proper operation of the comparator circuitry.
DD
falls below the low-battery threshold. All functional tests
Ionization Smoke Detector
R
LOWVSET
K = V
(th)set
= 960E3 × K / (0.6 – 1.6 × K) ,
/ (0.727 × V
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
with Interconnect
(th)set
(th)init
, the resistor should
) – 1 .
DD
and
6