RE46C165 Microchip Technology Inc., RE46C165 Datasheet - Page 13

• Manufacturer Part Number: RE46C165
• Description: Cmos Photoelectric Smoke Detector Asic With Interconnect, Timer Mode And Alarm Memory
• Manufacturer: Microchip Technology Inc.

3.0
3.1
With the external components specified in the Typical
Application for ROSC and COSC, the internal
oscillator has a nominal period of 10 ms. Normally the
analog circuitry is powered down to minimize standby
current (typically 4 µA at 9V). Once every 10 seconds
the detection circuitry (normal gain) is powered up
for 10 ms. Prior to completion of the 10 ms period, the
IRED pulse is active for 100 µs. At the conclusion of the
10 ms period, the photo amplifier is compared to an
internal reference to determine the chamber status and
latched. If a smoke condition is present, the period to
the next detection decreases and additional checks are
made. Three consecutive smoke detections will cause
the device to go into alarm, and the horn circuit and
interconnect will be active.
Once every 43 seconds, the status of the battery
voltage is checked. This status is checked and latched
at the conclusion of the LED pulse. In addition, once
every 43 seconds, the chamber is activated and, using
the high gain mode (capacitor C1), a check of the
chamber is made by amplifying background reflections.
If either the low battery or the photo chamber test fails,
the horn will chirp for 10 ms every 43 seconds.
The oscillator period is determined by the values of R9,
R12 and C5 (see the Typical Application figure). The
oscillator period is as follows:
EQUATION 3-1:
3.2
A comparator compares the photo amplifier output to
an internal reference voltage. If the required number of
consecutive smoke conditions is met, the device will go
into local alarm and the horn will be active. In local
alarm, the C2 gain is internally increased by
approximately 10% to provide alarm hysteresis.
3.3
If the TEST input pin is activated (V
detection is sampled at a high rate. The RE46C166/8
device samples at a period of 330 ms. The
RE46C165/7 device has a first sample delay of up to
330 ms. After one sample, the smoke detection rate
increases to once every 250 ms. In this mode the high
gain capacitor C1 is selected, and background
reflections are used to simulate a smoke condition.
 2010 Microchip Technology Inc.
Where:
DEVICE DESCRIPTION
Internal Timing
Smoke Detection Circuit
Push-to-Test Operation
T = TR + TF
TR = .693 * R12 * C5
TF = .693 * R9 * C5
IH4
), the smoke
After the required three consecutive detections, the
device will go into a local alarm condition. When the
TEST input is deactivated (V
cycle, the normal gain capacitor C2 is selected. The
detection rate continues once every 330 ms for the
RE46C166/8, and every 250 ms while the horn is not
sounding
consecutive no smoke conditions are detected, the
device returns to standby timing.
Push-to-test will not work while the alarm memory is
set. The alarm memory notification will be activated
instead.
3.4
In standby, the LED is pulsed on for 10 ms, every
43 seconds. In a local alarm condition or the push-to-
test alarm, the LED pulse frequency is increased once
every.5 seconds. In the case of a remote alarm, the
LED is not active. In the Timer mode of operation, the
LED is pulsed on for 10 ms every 10 seconds.
3.5
The bidirectional I/O pin allows the interconnection of
multiple detectors. In a local alarm condition, this pin is
driven high immediately through a constant current
source. Shorting this output to ground will not cause
excessive current. The I/O is ignored as an input during
a local alarm.
The I/O pin has a 280k nominal pull-down resistor, so
the pin may be left unconnected.
The I/O pin also has an NMOS discharge device that is
active for 1 second after the conclusion of any type of
local alarm. This device helps to quickly discharge any
capacitance associated with the interconnect line.
If a remote active high signal is detected, the device
goes into remote alarm and the horn will be active.
Internal protection circuitry allows for the signaling unit
to have a higher supply voltage than the signaled unit,
without excessive current draw.
The interconnect input has a digital filter that ensures
filtering out pulses of up to 300 ms. Filter pulses will be
ignored and not affect internal timing of the part. This
allows for interconnection to other types of alarms
(carbon monoxide for example) that may have a pulsed
interconnect signal.
The remote alarm delay (370 ms to 1.27s) specifies the
time from the interconnect going active to sounding the
piezo horn alarm.
LED Pulse
Interconnect
for
RE46C165/6/7/8
the
RE46C165/7.
IL4
) and after one clock
DS22251A-page 13
When
three