LM91 Diode Input Digital Temperature Sensor with Two-Wire Interface
November 2001
LM91
Diode Input Digital Temperature Sensor with Two-Wire
Interface
General Description
The LM91 is a remote diode temperature sensor,
Delta-Sigma analog-to-digital converter, and digital
over-temperature detector with an SMBus
™
interface. The
LM91 senses its own temperature as well as the tempera-
ture of a target IC with a diode junction, such as a Pentium
®
II processor or a diode connected 2N3904. A diode junction
(semiconductor junction) is required on the target IC’s die. A
host can query the LM91 at any time to read the temperature
of this diode as well as the temperature state of the LM91
itself. A T_CRIT_A interrupt output becomes active when the
temperature is greater than a programmable comparator
limit, T_CRIT.
The host can program as well as read back the state of the
T_CRIT register. Power up default values for T_CRIT are as
shown in the ordering information table. Three state logic
inputs allow two pins (ADD0, ADD1) to select up to 9 SMBus
address locations for the LM91.
n
Register readback capability
n
7 bit plus sign temperature data format
n
2 address select lines enable 9 LM91s to be connected
to a single bus
Key Specifications
j
Supply Voltage
j
Supply Current
j
Local Temperature Accuracy
j
Remote Diode Temperature Accuracy
3.0V - 3.6V
1 mA (max)
±
1.0˚C (typ)
±
4˚C (max)
±
6˚C (max)
+60˚C to +100˚C
0˚C to +125˚C
Applications
n
n
n
n
n
System Thermal Management
Personal Computers
Electronic Test Equipment
Office Electronics
HVAC
Features
n
Directly senses die temperature of remote ICs
n
Senses temperature of remote diodes
n
SMBus compatible interface, supports SMBus Timeout
Simplified Block Diagram
20034301
#
Indicates Active Low (”NOT“)
SMBus
™
is a trademark of the Intel Corporation.
Pentium
®
II processor is a registered trademark of the Intel Corporation.
I2C
®
is a registered trademark of the Philips Corporation.
© 2001 National Semiconductor Corporation
DS200343
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