SMOKE DETECTOR. M75310 Datasheet
MOSDESIGN SEMICONDUCTOR CORP.
PHOTOELECTRIC SMOKE DETECTOR
The M75310 is a very low-power IC providing all of the required features for a photoelectric type smoke detector.
This device can be used in conjunction with an infrared photoelectric chamber to sense scattered light from smoke particles.
A variable-gain photo amplifier can be directly interfaced to an infrared emitter / detector pair. The amplifier gain levels are
Determined by two external capacitors that are then internally selected depending on the operating mode. Low gain is selected
during standby and timer modes. During a local alarm this low gain is increased (internally) by ~ 10% to reduce false triggering.
High gain is used during the push-button test and during standby to periodically monitor the chamber sensitivity.
‧ Interconnect up to 50 detectors.
‧ Piezoelectric horn driver.
‧ Power-on reset.
‧ Built-in circuits to reduce false triggering.
‧ 6V to 12V operating voltage range.
‧ Average Supply Current：8μA
‧ ESD-Protection circuitry on all pins.
‧ Temporal horn pattern.
‧ Smoke detector.
MOSDESIGN SEMICONDUCTOR CORP.
PHOTOELECTRIC SMOKE DETECTOR
PIN AND CIRCUIT DESCRIPTION
Pin No Pin Name
A capacitor connected to this pin determines the gain of the photo amplifier during the push-to-test mode and
during the chamber monitor test. A typical value for this high-gain mode is 0.047μF but should be selected
1 C1 based on the photo chamber background reflections reaching the detector and the desired level of sensitivity.
Ae ≒ 1 + ( C1 / 10 ) where C1 is in pF. Ae should not exceed 10,000.
A capacitor connected to this pin determines the gain of the photo amplifier during standby. A typical value for
2 C2 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. Ae ≒ 1 + ( C2 / 10 ) where C2 is in pF. Ae should not exceed 10,000.
This is the input to the photo amplifier and is connected to the cathode of the photo diode. The photo diode is
operated at zero bias and should have low dark leakage current and low capacitance.
This output provides a strobed, regulated voltage of VDD-5V. The minus side of all internal and external
photo amplifier circuitry is referenced to this pin.
5 VDD This pin is connected to the most-positive supply potential.
This output provides a pulsed base current for the external NPN transistor, which drives the IR emitter. Its beta
6 IRED should be greater than 100. The IRED output is not active, to minimize noise impact, when the horn and
visible LED outputs are active.
A connection at this 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 this pin to be ignored as an input.
7 I/O 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 alarm. This pin also has an on-chip pull-
down resistor and must be left unconnected if not used. In application, there is a series current-limiting resistor
to other smoke alarms.
These three pins are used in conjunction with external passive components and a self-resonating piezoelectric
transducer. HORN1 is connected to the piezo metal support electrode; the complementary output, HORN2, is
connected to the ceramic electrode and the FEEDBACK input to the feedback electrode.
A continuous modulated tone indicates either a local or remote alarm condition. A short (10ms) chirp indicates
low-battery chirp occurs almost simultaneous
must be connected to VDD or VSS.
This open-drain NMOS output is used to directly drive a visible LED. The low-battery test does not occur
coincident with any other test or alarm signal. The LED also indicates detector status as follows (with
11 LED component values as in the typical application , all times nominal)：
Standby ─ Pulses every 43 seconds. Local Smoke ─ Pulses every 0.67 seconds.
Remote Alarm ─ No pulses.
Test Mode ─ Pulses every 0.67 seconds.
A capacitor between this pin and VDD, along with a parallel resistor, forms part of a two-terminal oscillator
12 OSCC and sets the internal clock low time. With component values as shown, this nominal time is 11 ms and
essentially the oscillator period.
A resistor between this pin and OSCC (pin 12) is part of the two-terminal oscillator and sets the internal clock
13 OSCR high time, which is also the IRED pulse width. With component values as shown , this nominal time is 105μs .
14 VSS This pin is connected to the most negative supply potential (usually ground).
This pin is connected to an external voltage, which determines the low-supply alarm threshold. The trip
15 TRIP voltage is obtained through a resistor divider connected between the VDD and LED pins. The low-supply
alarm threshold voltage ( in volts ) ≒ ( 5R15/R14 ) + 5 where R15 and R14 are in the same units.
This pin has an internal pull-down device and is used to manually invoke a test mode. The Push-to-Test Mode
is initiated by a high logic level on this pin (usually the depression of a normally open push-button switch to
VDD). After one oscillator cycle, IRED pulse every 336 ms (nominal) and amplifier gain is increased by
internal selection of C1. Background reflections in the smoke chamber can be used to simulate a smoke
condition. After the third IRED pulse, a successful test (three consecutive simulated smoke conditions) activates
the horn drivers and the I/O pin. When the push-button is released, the input returns to VSS due to the internal
pull down. After one oscillator cycle, the amplifier gain returns to normal and after three additional IRED pulse
(less than one second), the device exits this mode and returns to standby.