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The LM89 is an 11-bit digital temperature sensor with a 2-wire System Management Bus (SMBus) serial interface. The LM89 accurately measures its own temperature as well as the temperature of an external device, such as processor thermal diode or diode-connected transistor such as the 2N3904. The temperature of any ASIC, GPU, FPGA or MCU can be accurately determined using the LM89 as long as a dedicated diode (semiconductor junction) is available on the target die. The LM89 has an Offset register to allow calibration for different nonideality factors without requiring software management.

Activation of the ALERT occurs when any temperature goes outside a preprogrammed window set by the HIGH and LOW limit registers or exceeds the T_CRIT limit. Activation of the T_CRIT_A occurs when any temperature exceeds the T_CRIT programmed limit.

The LM89 is pin and register compatible with the LM86, LM90, LM99, On Semiconductor ADM1032 and Maxim MAX6657/8.

The LM89C and the LM89-1C have the same functions but different SMBus slave addresses, allowing multiple LM89's on a bus. LM89-1D’s default local T_CRIT temperature limit is 105°C; all other versions are 85°C.