LM75
01265806
FIGURE 3. Printed Circuit Board Used for Thermal Resistance Specifications
Typical Performance Characteristics
Static Quiescent Current vs
Temperature
Dynamic Quiescent Current vs
Temperature
Accuracy vs Temperature
01265816
01265817
01265818
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
2
C 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:
1. 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.
2.
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 T
HYST
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
register via the I
2
C interface. Once O.S. has been activated
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