RE46C190 Datasheet, PDF (14/42 Pages) Microchip Technology – CMOS Low Voltage Photoelectric Smoke Detector ASIC with Interconnect

RE46C190
3.5 Interconnect Operation
The bidirectional IO pin allows the interconnection of
multiple detectors. In a Local Alarm condition, this pin
is driven high (High Boost) immediately through a
constant current source. Shorting this output to ground
will not cause excessive current. The IO is ignored as
input during a Local Alarm.
The IO pin also has an NMOS discharge device that is
active for 1.3 seconds 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.
RLED will be off, indicating a Remote Alarm condition.
Internal protection circuitry allows the signaling unit to
have a higher supply voltage than the signaled unit,
without excessive current draw.
The interconnect input has a 336 ms nominal digital
filter. This allows the interconnection to other types of
alarms (carbon monoxide, for example) that may have
a pulsed interconnect signal.
3.6 Reduced Sensitivity Mode
A Reduced Sensitivity or Hush mode is initiated by
activating the TEST input (V_IH). If the TEST input is
activated during a Local Alarm, the unit is immediately
reset out of the alarm condition, and the horn is
silenced. When the TEST input is deactivated (V_IL), the
device enters into a 9-minute nominal Hush mode.
During this period, the HUSH integration limit is
selected. The hush gain is user programmable. In
Reduced Sensitivity mode, the RLED flashes for 10 ms
every 10 seconds to indicate that the mode is active.
As an option, the Hush mode will be cancelled if any of
the following conditions exist:
• Reduced sensitivity threshold is exceeded
(high smoke level)
• An interconnect alarm occurs
• TEST input is activated again
3.7 Local Alarm Memory
An Alarm Memory feature allows easy identification of
any unit that had previously been in a Local Alarm
condition. If a detector has entered a Local Alarm,
when it exits that Local Alarm, the Alarm Memory latch
is set. Initially the GLED can be used to visually identify
any unit that had previously been in a Local Alarm
condition. The GLED flashes three times spaced
1.3 seconds apart. This pattern will repeat every
43 seconds. The duration of the flash is 10 ms. In order
to preserve battery power, this visual indication will stop
after a period of 24 hours. The user will still be able to
identify a unit with an active alarm memory by pressing
the Push-to-Test button. When this button is active, the
horn will chirp for 10 ms every 250 ms.
If the Alarm Memory condition is set, then any time the
Push-to-Test button is pressed and released, the Alarm
Memory latch is reset.
The initial 24 hour visual indication is not displayed if a
low battery condition exists.
3.8 End of Life Indicator
As an option, after every 14 days of continuous
operation, the device will read a stored age count from
the EEPROM and increment this count. After 10 years
of powered operation, an audible warning will occur
indicating that the unit should be replaced. This
indicator will be similar to the chamber test failure
warning in that the horn will pulse on three times for
10 ms separated by 330 ms every 43 seconds. This
indicator will be separated from the low battery
indicator by approximately 20 seconds.
3.9 Photo Chamber Long Term Drift
Adjustment
As an option, the design includes a Long Term Drift
Adjustment for the photo chamber. If this option is
selected, during calibration a normal no-smoke
baseline integration measurement is made and stored
in EEPROM. During normal operation, a new baseline
is calculated by making 64 integration measurements
over a period of 8 hours. These measurements are
averaged and compared to the original baseline stored
during calibration to calculate the long term drift. All
four limits stored during calibration are adjusted by this
drift factor. Drift sampling is suspended during Hush,
Local Smoke and Remote Smoke conditions.
DS22271A-page 14
 2010 Microchip Technology Inc.