BL59A65
Circuit Characteristic
The gain is determined by external capacitor C1 and C2. A capacitor
connected to C2 determines the gain of the photo amplifier during standby. A
typical value for this low-gain mode is 4700 pF but should be selected based on
a specific photo chamber and the desired level of sensitivity to smoke.
AV= 1+(C2/10) where C2 is in pF. This gain increases by a nominal 10% after a
local alarm is detected (three consecutive detections).
I/O pin allows multiple smoke detectors to be interconnected. If a local smoke
condition occurs, this pin is driven high. As an input, this pin is sampled
nominally every 1.35 seconds during standby. Any local alarm condition
causes I/O to be ignored as an input. An internal nmos device acts as a charge
dump to aid in applications involving a large (distributed) capacitance. The
charge dump is activated at the end of local or test mode.
LED pin is an output pin, which is used to directly drive a visible LED. The load
for the low-battery test is applied to this output. The low-battery test does not
occur coincident with any other test or alarm signal. The LED also indicates
detector status as follows (with component values as in the typical application,
all times nominal):
Standby - Pulses every 43 seconds.
Local Smoke - Pulses every 0.67 second.
Remote Alarm - No pulses.
Test Mode - Pulses every 0.67 second.
Timer Mode - Pulses every 10 seconds
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