Rainbow Electronics LM75 - Manual (Page 7)

Typical Performance Characteristics
Static Quiescent Current vs
Temperature
Dynamic Quiescent Current vs
Temperature 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
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 series of readings, the number of which is
user-selectable, to user-programmable setpoint and hyster-
esis 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
01265806
FIGURE 3. Printed Circuit Board Used for Thermal Resistance Specifications
LM75
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