LM75BIM-3 View Datasheet(PDF) - Maxim Integrated
Part Name
Description
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LM75BIM-3 Datasheet PDF : 12 Pages
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Digital Temperature Sensor and Thermal
Watchdog with 2-Wire Interface
Detailed Description
The LM75 temperature sensor measures temperature
and converts the data into digital form using a band-
gap type temperature sensor and a 9-bit sigma-delta
ADC. An I2C-compatible 2-wire serial interface allows
access to conversion results. The LM75 accepts stan-
dard I2C commands to read the data, set the overtem-
perature alarm (OS) trip thresholds, and configure other
characteristics. While reading the Temperature register,
any changes in temperature are ignored until the read
is completed. The Temperature register is updated for
the new temperature measurement upon completion of
the read operation.
OS Output, TOS, and THYST Limits
In comparator mode (see Figure 1), the open-drain OS
output asserts when the temperature rises above the
limit programmed into the TOS register, and becomes
high impedance when the temperature falls below the
limit set in the THYST register. In this mode the LM75
operates as a thermostat, and the OS output can be
used to take action to reduce the temperature (e.g.,
turn on a cooling fan, reduce clock speed, or shut
down the system).
In interrupt mode, exceeding TOS also asserts OS. OS
remains asserted until a read operation is performed on
any of the registers. Once OS has asserted due to
crossing above TOS and is then reset, it is asserted
again only when the temperature drops below THYST.
The output then remains asserted until it is reset by a
read. It is then asserted again if the temperature rises
above TOS, and so on. Putting the LM75 into shutdown
mode also resets OS.
Power-Up and Power-Down
The LM75 powers up to a known state, as indicated in
Table 2. Some of these settings are summarized as fol-
lowing:
• Comparator mode
• TOS = +80°C
• THYST = +75°C
• OS active low
• Command byte pointer = 0x00
I2C-Compatible Bus Interface
From a software perspective, the LM75 appears as a set
of byte-wide registers that contain temperature data,
alarm threshold values, and control bits. A standard I2C-
compatible, 2-wire serial interface reads temperature
data and writes control bits and alarm threshold data.
Each device responds to its own I2C slave address,
which is selected using A0, A1, and A2. See Table 1.
TOS
TEMPERATURE
THYST
OS OUTPUT
(COMPARATOR MODE)
OS SET ACTIVE LOW
OS OUTPUT
(INTERRUPT MODE)
OS SET ACTIVE LOW
READ
READ
OPERATION OPERATION
READ
OPERATION
Table 1. Slave Address
Figure 1. OS Output Temperature Response Diagram
BIT 7
1
BIT 6
0
BIT 5
0
BIT 4
1
BIT 3
A2
BIT 2
A1
BIT 1
A0
BIT 0
RD/W
Table 2. Register Functions
REGISTER NAME
Temperature
Configuration
THYST
TOS
X = Don’t care.
ADDRESS
(hex)
00
01
02
03
POR STATE
(hex)
000X
00
4B0X
500X
POR STATE (binary)
0000 0000 0XXX XXXX
0000 0000
0100 1011 0XXX XXXX
0101 0000 0XXX XXXX
POR STATE (°C)
—
—
75
80
READ/
WRITE
Read only
R/W
R/W
R/W
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