LM75 datasheet(7/18 Pages) NSC

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Typical Performance Characteristics

Static Quiescent Current vs Temperature

Dynamic Quiescent Current vs Temperature

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Accuracy vs Temperature

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1.0 Functional Description

The LM75 temperature sensor incorporates a band-gap type

temperature sensor and 9-bit ADC (Delta-Sigma Analog-to-

Digital Converter). The temperature data output of the LM75

is available at all times via the I

2C bus. If a conversion is in

progress, it will be stopped and restarted after the read. A

digital comparator is also incorporated that compares a se-

ries of readings, the number of which is user-selectable, to

user-programmable setpoint and hysteresis values. The

comparator trips the O.S. output line, which is programmable

for mode and polarity.

The LM75B contains all the functionality of the LM75C, plus

two additional features:

The LM75B has an integrated low-pass filter on both the

SDA and the SCL line. These filters increase communi-

cations reliability in noisy environments.

The LM75B also has a bus fault timeout feature. If the

SDA line is held low for longer than t

TIMEOUT (75 ms

minimum to 325 ms maximum) the LM75B will reset to

the IDLE state (SDA set to high impedance) and wait for

a new start condition.

1.1 O.S. OUTPUT, T

OS AND THYST LIMITS

In Comparator mode the O.S. Output behaves like a ther-

mostat. The output becomes active when temperature ex-

ceeds the T

OS limit, and leaves the active state when the

temperature drops below the T

HYST limit. In this mode the

O.S. output can be used to turn a cooling fan on, initiate an

emergency system shutdown, or reduce system clock

speed. Shutdown mode does not reset O.S. state in a com-

parator mode.

In Interrupt mode exceeding T

OS also makes O.S. active but

O.S. will remain active indefinitely until reset by reading any

2C interface. Once O.S. has been activated

by crossing T

OS, then reset, it can be activated again only by

Temperature going below T

HYST. Again, it will remain active

indefinitely until being reset by a read. Placing the LM75 in

shutdown mode also resets the O.S. Output.

1.2 POWER UP AND POWER DOWN

The LM75 always powers up in a known state. The power up

default conditions are:

Comparator mode

OS = 80˚C

HYST = 75˚C

O.S. active low

Pointer = “00”

If the LM75 is not connected to the I

2C bus on power up, it

will act as a stand-alone thermostat with the above tempera-

ture settings.

When the supply voltage is less than about 1.7V, the LM75 is

considered powered down. As the supply voltage rises

LM75 Datasheet(PDF) 7 Page - National Semiconductor (TI)

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