a5366 Allegro MicroSystems, Inc., a5366 Datasheet - Page 8

• Manufacturer Part Number: a5366
• Description: Photoelectric Smoke Detector With Interconnect And Timer
• Manufacturer: Allegro MicroSystems, Inc.

A5366
OSC CAP (Oscillator Capacitor) Pin
A capacitor between this pin and VDD, along with a parallel
resistor, forms part of a two-terminal oscillator and sets the inter-
nal clock low time. With component values shown, this nominal
time is 10.4 ms and essentially the oscillator period. The internal
clock low time can be calculated by:
TIMING RES (Timing Resistor) Pin
A resistor between this pin and OSC CAP is part of the two-ter-
minal oscillator and sets the internal clock high time, which is
also the IRED pulse width. With component values shown, this
time is nominally 105 μs. The internal clock high time can be
calculated by:
VSS Pin
This pin is connected to the negative supply potential (usually
ground).
HUSH Pin
This input pin has an internal pull-down device and serves two
purposes in standby mode. It serves to enable/disable entering
the internal 10-minute (nominal) “hush” timer mode, and also
as the reference for the smoke comparator during timer mode.
When the voltage on this pin is greater than 1.5 V, entering timer
mode is enabled, and a high-to-low transition on TEST resets
and starts timer mode. If use of timer mode is not desired, this
pin can be connected to VSS or left open, and a voltage of less
than 0.5 V on the pin will disable timer mode. During timer
mode, the smoke comparator reference is established by a resis-
tive divider (Rx1 and Rx2) between the VDD and STROBE
pins and allows the detector to operate with reduced sensitivity
during timer mode. This allows the user to hush alarms caused
by nuisance smoke or steam (such as from cooking). When not
in timer mode, the smoke comparator reference is set internally
to approximately V
TEST Pin
This pin has an internal pull-down device and is used to manu-
ally invoke two test modes and timer mode.
Push-to-Test mode is initiated by a voltage greater than approxi-
mately V
normally-open pushbutton switch to VDD). After one oscilla-
tor cycle, the amplifier gain is increased by internal selection
of C1 so that background reflections in the smoke chamber can
be used to simulate a smoke condition, and IRED pulses every
252 ms (nominal). After the third IRED pulse (three consecu-
tive simulated smoke conditions), the successful test activates
DD
– 0.5 V on this pin (usually the depression of a
T
T
high
low
= 0.693 × R
= 0.693 × R
DD
– 3.5 V.
TIMINGRES
OSCCAP
× C
× C
OSCCAP
OSCCAP
.
.
Photoelectric Smoke Detector
the horn drivers and the I/O pin, and the LED blinks once every
0.5 s. If the test fails, the LED will not blink, the horn will not
sound, and the I/O pin will remain low. When the pushbutton is
released, the input returns to V
After one oscillator cycle, the amplifier gain returns to normal,
and after three additional IRED pulses (less than one second), the
device exits this mode and returns to standby. This high-to-low
transition on TEST also resets and starts the 10-minute (nominal)
“hush” timer mode, if the mode is enabled via the HUSH pin.
Diagnostic Test/Calibration Mode is available to facilitate
calibration and test of the IC and the assembled detector. It is
initiated by pulling TEST below V
400 μA from the pin for at least one clock cycle on OSC CAP.
The current should not exceed 800 μA and under these condi-
tions, TEST pin voltage will clamp at approximately one diode
drop below V
through a 12 kΩ resistor. In this mode, certain device pins are
reconfigured as described in table 1. The IRED pulse rate is
Table 1. Alternate Pin Configuration During Diagnostic
Test/Calibration Mode
Pin Name
with Interconnect and Timer
OSC CAP
HORN1
FEED-
HUSH
BACK
LED
I/O
SS
Disabled as an output. A logic high on this pin places the
photoamplifier output on pin C1 or C2 as determined by
the HUSH pin. The amplifier output appears as pulses.
If the I/O pin is high, this pin controls the amplifier gain
capacitor. If this pin is low, normal gain is selected and
the amplifier output is on pin C1. If this pin is high,
supervisory gain is selected and the amplifier output is
on pin C2.
If the I/O pin is high and the HUSH pin is low (normal
gain), taking this pin to a high logic level increases the
amplifier gain by ≈10% (hysteresis).
This pin may be driven by an external clock source.
Driving this pin low and high drives the internal clock low
and high. The external RC network may remain intact.
This pin is reconfigured as the smoke integrator output.
Three consecutive smoke detections will cause this pin
to go high and three consecutive no-smoke detections
cause this pin to go low.
This pin becomes a low-battery indicator. The open-drain
NMOS output is normally off. If V
battery threshold, the output turns on.
. One option is to connect TEST to a –5 V supply
Alternate Configuration
115 Northeast Cutoff
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Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
SS
due to the internal pull down.
SS
by continuously drawing
DD
falls below the low-
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