Rainbow Electronics LM99 - Manual

LM99
± 1˚C Accurate, High Temperature, Remote Diode
Temperature Sensor with Two-Wire Interface
General Description
The LM99 is an 11-bit remote diode temperature sensor with
a 2-wire System Management Bus (SMBus) serial interface.
The LM99 accurately measures: (1) its own temperature and
(2) the temperature of a remote diode-connected transistor
such as the 2N3904 or a thermal diode commonly found on
Graphics Processor Units (GPU), Computer Processor Units
(CPU or other ASICs. The LM99 remote diode temperature
sensor shifts the temperature from the remote sensor down
16˚C and operates on that shifted temperature:
T
ACTUAL DIODE JUNCTION
= T
LM99
+ 16˚C
The local temperature reading requires no offset.
The LM99 has an Offset Register which provides a means
for precise matching to various thermal diodes. Contact
hardware.monitor
@ nsc.com for the latest details.
The LM99 and LM99-1 have the same functions but different
SMBus slave addresses. This allows for one of each to be on
the same bus at the same time.
Activation of the ALERT output occurs when any tempera-
ture goes outside a preprogrammed window set by the HIGH
and LOW temperature limit registers or exceeds the T_CRIT
temperature limit. Activation of the T_CRIT_A occurs when
any temperature exceeds the T_CRIT programmed limit.
Features
n Accurately senses the temperature of remote diodes
n Offset register allows use of a variety of thermal diodes
n On-board local temperature sensing
n 10 bit plus sign remote diode temperature data format,
0.125 ˚C resolution
n T_CRIT_A output useful for system shutdown
n ALERT output supports SMBus 2.0 protocol
n SMBus 2.0 compatible interface, supports TIMEOUT
n 8-pin MSOP package
Key Specifications
j Supply Voltage 3.0 V to 3.6 V
j Supply Current 0.8 mA (typ)
j Local Temp Accuracy (includes quantization error)
T
A
= 25˚C to 125˚C ± 3.0˚C (max)
j Remote Diode Temp Accuracy (includes quantization
error)
T
A
= 30˚C to 50˚C, T
D
= 120˚C to 140˚C ± 1.0˚C (max)
T
A
= 0˚C to 85˚C, T
D
= 25˚C to 140˚C ± 3.0˚C (max)
Applications
n Graphics Processor Thermal Management
n Computer Processor Thermal Management
n Electronic Test Equipment
n Office Electronics
Simplified Block Diagram
20053801
NVIDIA ® is a registered trademark of NVIDIA Corporation.
GeForce ™ is a trademark of NVIDIA Corporation.
Intel ® and Pentium ® are registered trademarks of Intel Corporation.
July 2003
LM99
±
1˚C
Accurate,
High
T
emperature,
Remote
Diode
T
emperature
Sensor
with
T
wo-W
ire
Interface
© 2003 National Semiconductor Corporation DS200538 www.national.com