1FEATURES
2• Accurately Senses the Temperature of Remote
Diodes
• Offset Register Allows Use of a Variety of
Thermal Diodes
• On-board Local Temperature Sensing
• 10 Bit Plus Sign Remote Diode Temperature
Data Format, 0.125 °C Resolution
• T_CRIT_A Output Useful for System Shutdown
• ALERT Output Supports SMBus 2.0 Protocol
• SMBus 2.0 Compatible Interface, Supports
TIMEOUT
• 8-Pin VSSOP Package

APPLICATIONS
• Graphics Processor Thermal Management
• Computer Processor Thermal Management
• Electronic Test Equipment
• Office Electronics

KEY SPECIFICATIONS
• Supply Voltage 3.0 V to 3.6 V
• Supply Current 0.8 mA (typ)
• Local Temp Accuracy
(Includes Quantization error)
– TA = 25°C to 125°C ±3.0°C (Max)
• Remote Diode Temp Accuracy
(Includes Quantization Error)
– TA = 30°C to 50°C, TD = 120°C to 140°C
±1.0°C (Max)
– TA = 0°C to 85°C, TD = 25°C to 140°C ±3.0°C
(Max)

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:
TACTUAL DIODE JUNCTION = TLM99 + 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.
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
temperature 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.