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MC145011 Просмотр технического описания (PDF) - Motorola => Freescale

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MC145011 Datasheet PDF : 12 Pages
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VDD (Pin 5)
This pin is connected to the positive supply potential and
may range from + 6 to + 12 V with respect to VSS.
IRED (Pin 6)
This output provides pulsed base current for external NPN
transistor Q1 used as the infrared emitter driver. Q1 must
have β 100. At 10 mA, the temperature coefficient of the
output voltage is typically + 0.5%/°C from – 10° to 60°C. The
supply–voltage coefficient (line regulation) is ± 0.2%/V maxi-
mum from 6 to 12 V. The IRED pulse width (active–high) is
determined by external components R1 and C3. With a
100 k/1500 pF combination, the nominal width is 105 µs.
To minimize noise impact, IRED is not active when the vis-
ible LED and horn outputs are active. IRED is active near the
end of Strobe pulses for Smoke Tests, Chamber Sensitivity
Test, and Pushbutton Test.
I/O (Pin 7)
This pin can be used to connect up to 40 units together in
a wired–OR configuration for common signaling. VSS is used
as the return. An on–chip current sink minimizes noise pick
up during non–smoke conditions and eliminates the need for
an external pull–down resistor to complete the wired–OR.
Remote units at lower supply voltages do not draw excessive
current from a sending unit at a higher supply voltage.
I/O can also be used to activate escape lights, auxiliary
alarms, remote alarms, and/or auto–dialers.
As an input, this pin feeds a positive–edge–triggered flip–
flop whose output is sampled nominally every 625 ms during
standby (using the recommended component values). A
local–smoke condition or the pushbutton–test mode forces
this current–limited output to source current. All input signals
are ignored when I/O is sourcing current.
I/O is disabled by the on–chip power–on reset to elimi-
nate nuisance signaling during battery changes or system
power–up.
If unused, I/O must be left unconnected.
BRASS (Pin 8)
This half of the push–pull driver output is connected to
the metal support electrode of a piezoelectric audio trans-
ducer and to the horn–starting resistor. A continuous mod-
ulated tone from the transducer is a smoke alarm
indicating either local or remote smoke. A short beep or
chirp is a trouble alarm indicating a low supply or degraded
chamber sensitivity.
SILVER (Pin 9)
This half of the push–pull driver output is connected to the
ceramic electrode of a piezoelectric transducer and to the
horn–starting capacitor.
FEEDBACK (Pin 10)
This input is connected to both the feedback electrode of a
self–resonating piezoelectric transducer and the horn–start-
ing resistor and capacitor through current–limiting resistor
R4. If unused, this pin must be tied to VSS or VDD.
MC145011
LED (Pin 11)
This active–low open–drain output directly drives an exter-
nal visible LED.
The load for the low–supply test is applied by this output.
This low–supply test is non–coincident with the smoke
tests, chamber sensitivity test, pushbutton test, or any
alarm signals.
The LED also provides a visual indication of the detector
status as follows, assuming the component values shown in
Figure 5:
Standby (includes low–supply and chamber sensitivity
tests) — constantly illuminated
Local Smoke — constantly extinguished
Remote Smoke — constantly illuminated
Pushbutton Test — constantly extinguished (system OK);
constantly illuminated (system problem)
OSC (Pin 12)
This pin is used in conjunction with external resistor R2
(10 M) to VDD and external capacitor C3 (1500 pF) to VDD
to form an oscillator with a nominal period of 10.5 ms.
R1 (Pin 13)
This pin is used in conjunction with resistor R1 (100 k) to
pin 12 and C3 (1500 pF, see pin 12 description) to determine
the IRED pulse width. With this RC combination, the nominal
pulse width is 105 µs.
VSS (Pin 14)
This pin is the negative supply potential and the return for
the I/O pin. Pin 14 is usually tied to ground.
LOW–SUPPLY TRIP (Pin 15)
This pin is connected to an external voltage which deter-
mines the low–supply alarm threshold. The trip voltage is
obtained through a resistor divider connected between the
VDD and LED pins. The low–supply alarm threshold voltage
(in volts) (5R7/R6) + 5 where R6 and R7 are in the same
units.
TEST (Pin 16)
This input has an on–chip pull–down device and is used to
manually invoke a test mode.
The Pushbutton Test mode is initiated by a high level at pin
16 (usually depression of a S.P.S.T. normally–open pushbut-
ton switch to VDD). After one oscillator cycle, IRED pulses
approximately every 336 ms, regardless of the presence of
smoke. Additionally, the amplifier gain is increased by auto-
matic selection of C1. Therefore, the background reflections
in the smoke chamber may be interpreted as smoke, gener-
ating a simulated–smoke condition. After the second IRED
pulse, a successful test activates the horn–driver and I/O cir-
cuits. The active I/O allows remote signaling for system test-
ing. When the Pushbutton Test switch is released, the Test
input returns to VSS due to the on–chip pull–down device. Af-
ter one oscillator cycle, the amplifier gain returns to normal,
thereby removing the simulated–smoke condition. After two
additional IRED pulses, less than a second, the IC exits the
alarm mode and returns to standby timing.
Motorola Sensor Device Data
9

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