LM75AIMX/NOPB National Semiconductor, LM75AIMX/NOPB Datasheet - Page 14

• Manufacturer Part Number: LM75AIMX/NOPB
• Description: IC TEMP SENSOR WATCHDOG 8-SOIC
• Manufacturer: National Semiconductor

Specifications of LM75AIMX/NOPB

• Function: Temp Sensor, Watchdog
• Topology: ADC (Sigma Delta), Comparator, Register Bank
• Sensor Type: Internal
• Sensing Temperature: -55°C ~ 125°C
• Output Type: I²C™
• Output Alarm: Yes
• Output Fan: Yes
• Voltage - Supply: 2.7 V ~ 5.5 V
• Operating Temperature: -55°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Temperature Sensor Function: Temp Sensor
• Interface Type: Serial (2-Wire)
• Resolution: 9b
• Package Type: SOIC N
• Operating Temperature (max): 125C
• Operating Temperature Classification: Military
• Operating Supply Voltage (min): 2.7V
• Operating Supply Voltage (typ): 3.3/5V
• Operating Supply Voltage (max): 5.5V
• For Use With: OM6285 - EVAL BOARD I2C-2002-1A568-4002 - DEMO BOARD I2C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM75AIMX

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2.0 Application Hints
To get the expected results when measuring temperature with
an integrated circuit temperature sensor like the LM75A, it is
important to understand that the sensor measures its own die
temperature. For the LM75A, the best thermal path between
the die and the outside world is through the LM75A's pins. In
the MSOP-8 package, the GND pin is directly connected to
the die, so the GND pin provides the best thermal path. If the
other pins are at different temperatures (unlikely, but possi-
ble), they will affect the die temperature, but not as strongly
as the GND pin. In the SO-8 package, none of the pins is
directly connected to the die, so they will all contribute simi-
larly to the die temperature. Because the pins represent a
good thermal path to the LM75A die, the LM75A will provide
an accurate measurement of the temperature of the printed
circuit board on which it is mounted. There is a less efficient
thermal path between the plastic package and the LM75A die.
If the ambient air temperature is significantly different from the
printed circuit board temperature, it will have a small effect on
the measured temperature.
In probe-type applications, the LM75A can be mounted inside
a sealed-end metal tube, and can then be dipped into a bath
or screwed into a threaded hole in a tank. As with any IC, the
LM75A and accompanying wiring and circuits must be kept
insulated and dry, to avoid leakage and corrosion. This is es-
3.0 Typical Applications
When using the two-wire interface: program O.S. for active high and connect O.S. directly to Q2's gate.
FIGURE 7. Simple Fan Controller, Interface Optional
14
pecially true if the circuit may operate at cold temperatures
where condensation can occur. Printed-circuit coatings and
varnishes such as Humiseal and epoxy paints or dips are of-
ten used to insure that moisture cannot corrode the LM75A
or its connections.
2.1 DIGITAL NOISE ISSUES
The LM75A features an integrated low-pass filter on both the
SCL and the SDA digital lines to mitigate the effects of bus
noise. Although this filtering makes the LM75A communica-
tion robust in noisy environments, good layout practices are
always recommended. Minimize noise coupling by keeping
digital traces away from switching power supplies. Also, en-
sure that digital lines containing high-speed data communi-
cations cross at right angles to the SDA and SCL lines.
Excessive noise coupling into the SDA and SCL lines on the
LM75A—specifically noise with amplitude greater than
400 mV
than 300mV above +V
below GND—may prevent successful serial communication
with the LM75A. Serial bus no-acknowledge is the most com-
mon symptom, causing unnecessary traffic on the bus. Al-
though the serial bus maximum frequency of communication
is only 400 kHz, care must be taken to ensure proper termi-
nation within a system with long printed circuit board traces
or multiple parts on the bus.
pp
(the LM75A’s typical hysteresis), overshoot greater
s
, and undershoot more than 300 mV
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