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PDF A5338 Data sheet ( Hoja de datos )
| Número de pieza | A5338 | |
| Descripción | Smoke Detector | |
| Fabricantes | Allegro MicroSystems | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de A5338 (archivo pdf) en la parte inferior de esta página. Total 8 Páginas | ||
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Package A, 16-lead DIP
A5338
Smoke Detector
with Interconnect and Timer
The A5338CA is a low-current, CMOS circuit
providing all of the required features for an ionization-
type smoke detector. A networking capability allows
as many as 125 units to be interconnected so that if
any unit senses smoke, all units will sound an alarm.
Approximate Scale 1:1
In addition, special features are incorporated to facili-
tate alignment and test of the finished smoke detector.
This device is designed to comply with Underwriters
Features
Laboratories Specification UL217.
The internal oscillator and timing circuitry keeps
Interconnect up to 125 detectors
Piezoelectric horn driver
Guard outputs for detector input
standby power to a minimum by powering down the
device for 1.66 seconds and sensing smoke for only
10 ms. Every 24 on/off cycles, a check is made for
low battery condition. By substituting other types of
Pulse testing for low battery
sensors, or a switch for the ionization detector, this
Power-on reset
very-lowwww.DataSheet4U.com power device can be used in numerous other
Internal reverse battery protection
Internal timer and control for reduced sensitivity
battery-operated safety/security applications.
The A5338CA is supplied in a low-cost, 16-pin
dual in-line plastic package. It is rated for continuous
Built-in hysteresis reduces false triggering
operation over the temperature range of 0°C to +50°C.
Typical Application
9V
50 kΩ
200 kΩ
Push to set
200 kΩ
To other units
+SUPPLY or
–SUPPLY
200 Ω
RLV
1 TIMER START
GUARD2 16
2
I/O
3
LOW-V SET
DETECT IN 15
A5338
GUARD1 14
4 TIMER OUT SENSIVITIVTY SET 13
5
LED
330 Ω
6
RT +SUPPLY
8.2 MΩ 7 TIMING RES
OSC CAP 12
HORN2 11
HORN1 10
1 μF
8
FEEDBACK
–SUPPLY 9
Smoke
Chamber
Push to test
COSC
0.1 μF
RS
+SUPPLY or
–SUPPLY
Horn
1 MΩ
200 kΩ
0.001 μF
26110.1
RST
Dwg. EC-005A
1 page  
A5338 Smoke Detector with Interconnect and Timer
Functional Description
The A5338 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 s
during no-smoke conditions. Every 1.67 s, internal power is
applied to the entire circuit and a check is made for smoke. Every
24 oscillator cycles (40 s total), the LED is pulsed and a check is
made for low battery by comparing VDD to an internal reference.
Because very low currents are used in the device, the oscillator
capacitor, COSC, at the OSC CAP pin should be a low-leakage
type (PTFE, polystyrene, or polypropylene).
Detector Circuitry. When smoke is detected, the resistor
divider network that sets the sensitivity (smoke trip point) is
altered to increase the voltage on the SENSITIVITY SET pin by
130 mV typical, when there are no external connections to the
SENSITIVITY SET pin or LOW-V SET pin. This provides hys-
teresis and reduces false triggering. An active guard is provided
on both GUARDx pins, adjacent to the DETECT IN detec-
tor input pin. The voltage at the GUARDx pins will be within
100 mV of DETECT IN. 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 protec-
tion 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 160
ms ON, and 80 ms OFF, typical. During the OFF time, smoke is
again checked and the circuit will inhibit further horn output if
smoke is not sensed. During smoke conditions, the low-battery-
warning is inhibited. The LED is driven at a 1 Hz rate, and will
only turn ON while the horn outputs are in the OFF state.
Sensitivity Adjust. The detector sensitivity to smoke is set
internally by a voltage divider connected between VDD and VSS.
The sensitivity can be externally adjusted to the individual char-
acteristics of the ionization chamber by connecting a resistor, RS,
between the SENSITIVITY SET pin and +SUPPLY, or between
SENSITIVITY SET pin and –SUPPLY.
Low Battery. The low-battery threshold is set internally by a
voltage divider connected between VDD and VSS. The threshold
can be increased by connecting a resistor, RLV, between the
LOW-V SETpin and +SUPPLY. The threshold can be decreased
by connecting RLV between LOW-V SETpin and –SUPPLY. The
battery voltage level is checked every 40 s during the 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 bat-
tery loading remains at 10 mA.
Timer. An internal timer is provided that can be used in various
configurations to allow for a period of reduced smoke detector
sensitivity, Hush mode. When a high-to-low transition occurs at
the TIMER START pin, the internal timer is reset, Timer mode is
enabled, and the circuit is reset to a no-alarm condition. Dur-
ing Hush mode, the LED will flash at a 10 s rate. If the level
of smoke is increased such that the reduced sensitivity level is
reached, the device will go into the alarm condition. The timer,
however, will continue to completion of the nominal 6.5 minute
period (232 oscillator cycles). If Timer mode is not used, the
TIMER START pin should be tied low. While in Hush mode, the
battery is checked. If a low-battery condition is detected, the low-
battery warning chirp will be activated.
I/O. The I/O pin provides a terminal to allow multiple smoke
detectors to be commoned. If any single unit detects smoke (I/O
is driven high), all connected units will sound their associated
horns after a nominal 3 s delay. The LED is suppressed when an
alarm is signaled from another interconnected unit. An inter-
nal NMOS device acts as a charge dump to aid in applications
involving a large (distributed) capacitance on the I/O pin. The
charge dump is activated only on the removal of a local alarm.
Testing. On power-up, all internal counters are reset. Internal
test circuitry allows for low-battery check by holding the
FEEDBACK and OSC CAP pins low during power-up, then
reducing VDD and monitoring HORN1. All functional tests can be
accelerated by driving OSC CAP with a 2 kHz square wave. The
10 ms strobe period must be maintained for proper operation of
the comparator circuitry.
26110.1
Allegro MicroSystems, Inc.
5
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
5 Page | ||
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| PDF Descargar | [ Datasheet A5338.PDF ] | |
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