MC145012P 查看數據表（PDF） - Freescale Semiconductor
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MC145012P
Freescale Semiconductor
MC145012P Datasheet PDF : 14 Pages
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Table 4. Pin Description (Continued)
Pin No. Pin Name
Description
4
STROBE This output provides a strobed, regulated voltage referenced to VDD. The temperature coefficient of this voltage is
± 0.2%/°C maximum from - 10° to 60°C. The supply-voltage coefficient (line regulation) is ± 0.2%/V maximum from 6.0 V
to 12 V. Strobe is tied to external resistor string R8, R9, and R10.
5
VDD
This pin is connected to the positive supply potential and may range from + 6.0 V to + 12 V with respect to VSS
CAUTION: In battery-powered applications, reverse-polarity protection must be provided externally.
6
IRED 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 maximum from 6.0 V to 12 V. The IRED pulse width (active-high)
is determined by external components R1 and C3. With a 100 kΩ/1500 pF combination, the nominal width is 105 µs.
To minimize noise impact, IRED is not active when the visible LED and horn outputs are active. IRED is active near the
end of strobe pulses for smoke tests, chamber sensitivity test, and push-button test.
7
I/O
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 1 second during
standby (using the recommended component values). A local-smoke condition or the push-button-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 eliminate nuisance signaling during battery changes or system power-up.
If unused, I/O must be left unconnected.
8
BRASS This half of the push-pull driver output is connected to the metal support electrode of a piezoelectric audio transducer
and to the horn-starting resistor. A continuous modulated 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.
9
SILVER This half of the push-pull driver output is connected to the metal support electrode of a piezoelectric audio transducer
and to the horn-starting resistor. A continuous modulated 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.
10 FEEDBACK This input is connected to both the feedback electrode of a self-resonating piezoelectric transducer and the horn-starting
resistor and capacitor through current-limiting resistor R4. If unused, this pin must be tied to VSS or VDD.
11
LED
This active-low open-drain output directly drives an external visible LED at the pulse rates indicated below. The pulse
width is equal to the OSC period.
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, push-button 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 8:
Standby (includes low-supply and chamber sensitivity tests) — Pulses every 32.4 seconds (typical)
Standby (includes low-supply and chamber sensitivity tests) — Pulses every 32.4 seconds (typical)
Local Smoke — Pulses every 0.51 seconds (typical)
Remote Smoke — No pulses
Push-button Test — Pulses every 0.51 seconds (typical)
12
OSC
This pin is used in conjunction with external resistor R2 (7.5 MΩ) to VDD and external capacitor C3 (1500 pF) to VDD to
form an oscillator with a nominal period of 7.9 ms (typical).
13
R1
This pin is used in conjunction with resistor R1 (100 kΩ) 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.
14
VSS
This pin is the negative supply potential and the return for the I/O pin. Pin 14 is usually tied to ground.
15
LOW- This pin is connected to an external voltage which determines the low-supply alarm threshold. The trip voltage is
SUPPLY obtained through a resistor divider connected between the VDD and LED pins. The low-supply alarm threshold voltage
TRIP
(in volts) ≈ (5R7/R6) + 5 where R6 and R7 are in the same units.
16
TEST This input has an on-chip pull-down device and is used to manually invoke a test mode.
The Push-button Test mode is initiated by a high level at Pin 16 (usually depression of a S.P.S.T. normally-open push-
button switch to VDD). After one oscillator cycle, IRED pulses approximately every 1.0 second, regardless of the presence
of smoke. Additionally, the amplifier gain is increased by automatic selection of C1. Therefore, the background reflections
in the smoke chamber may be interpreted as smoke, generating a simulated-smoke condition. After the second IRED
pulse, a successful test activates the horn-driver and I/O circuits. The active I/O allows remote signaling for system
testing. When the Push-button Test switch is released, the Test input returns to VSS due to the on-chip pull-down device.
After one oscillator cycle, the amplifier gain returns to normal, thereby removing the simulated-smoke condition. After two
additional IRED pulses, less than three seconds, the IC exits the alarm mode and returns to standby timing.
MC145012
10
Sensors
Freescale Semiconductor
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