Texas Instruments LM90CIMM

Overview

LM90CIMM from Texas Instruments is an 11-bit remote/local digital temperature sensor with SMBus 2.0 interface, ±3°C remote diode accuracy (at 30–50°C ambient, 60–100°C diode), 0.125°C remote resolution, and dual thermal monitoring capability for CPU/ASIC die and local PCB temperature. It is used in laptop and server thermal management systems to trigger fan control or shutdown via T_CRIT_A and ALERT outputs.

For engineers reviewing the LM90CIMM datasheet, LM90CIMM pinout, LM90CIMM application, or LM90CIMM equivalent, key selection considerations include remote diode non-ideality compensation, SMBus 2.0 TIMEOUT support, open-drain alarm outputs with hysteresis, and factory-trimmed ±3°C accuracy for mobile Pentium III thermal diodes.

Technical Context

The LM90CIMM implements a delta-V_BE sensing architecture for both local silicon and remote bipolar junction diodes, with separate 8-bit local (1°C LSB) and 11-bit remote (0.125°C LSB) temperature data formats. Its digital comparators monitor local and remote readings against independently programmable HIGH, LOW, and T_CRIT limit registers.

It features dual open-drain alarm outputs: ALERT supports SMBus ALERT protocol, interrupt flag, or comparator modes via configuration bit D0 in the FILTER register; T_CRIT_A provides dedicated critical-temperature shutdown with hysteresis set by the TH register and remains active until temperature falls below T_CRIT − TH.

Key Specifications

Pinout & Package

LM90CIMM is housed in an 8-pin VSSOP (DGK) package - 2.3 mm × 2.0 mm, 0.5 mm pitch - optimized for space-constrained thermal sensing near processors or ASICs.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar remote/local digital temperature sensing applications.

Compared with LM90CIMM, LM86CIMM offers identical mechanical and functional drop-in capability but omits D− voltage limits, while MAX6657ASA+ trades resolution, alarm architecture, and diagnostics for lower unit cost and alternate addressing-making LM90CIMM optimal for robust, high-accuracy thermal safety systems.

Availability

LM90CIMM is available at Aetrix Electronics and suitable for laptop thermal management, server blade cooling, and industrial embedded controller applications requiring stable component supply and long-term lifecycle support.

Supply support for LM90CIMM includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor leader specializing in analog, embedded processing, and connectivity technologies, with decades of expertise in precision sensing and power-efficient IC design.

The LM90CIMM belongs to TI's precision analog temperature sensor product line, engineered specifically for high-accuracy, dual-point thermal monitoring in computing and industrial platforms where reliability and SMBus interoperability are critical.

FAQ

What is the remote diode accuracy specification for LM90CIMM across its full operating range?

The LM90CIMM achieves ±3.0°C maximum remote diode temperature accuracy when ambient temperature is 30–50°C and remote diode junction temperature is 60–100°C-this is factory-trimmed for mobile Pentium III thermal diodes with 1.008 non-ideality factor. Over the broader range of 0–85°C ambient and 25–125°C diode temperature, accuracy degrades to ±4.0°C maximum. These values include quantization error and are verified per SNIS126A datasheet specifications.

Does LM90CIMM support SMBus TIMEOUT detection, and what is the required low-pulse duration?

Yes, LM90CIMM fully supports SMBus 2.0 TIMEOUT detection. The device resets its SMBus state machine when SMBData or SMBCLK is held low for longer than tTIMEOUT, specified as 25–35 ms. This feature prevents bus lockup during communication faults and is implemented per SMBus 2.0 compliance requirements outlined in the LM90CIMM datasheet.

How does the T_CRIT_A output behave when the remote diode is open-circuited?

When the remote diode is open-circuited, the LM90CIMM sets the OPEN bit (D2) in the Status Register and loads +127°C into RTHB and 0 into RTLB-but T_CRIT_A remains inactive because the OPEN condition itself does not trigger T_CRIT comparison. Only actual temperature readings exceeding the T_CRIT register value will assert T_CRIT_A; thus, an open diode alone will not cause hardware shutdown unless the +127°C reading exceeds the programmed T_CRIT limit.

Can LM90CIMM measure temperature using a discrete transistor instead of an IC-integrated diode?

Yes, LM90CIMM can accurately sense temperature using discrete NPN transistors such as the 2N3904 as remote thermal diodes. Its D+ current source (110–315 µA) and D− sink are designed to bias standard diode-connected transistors. The offset registers (RTOLB/RTOHB) allow calibration for non-idealities outside the default 1.008 factor, making it suitable for third-party discrete thermal sensing solutions.

What is the power-on reset behavior of LM90CIMM regarding temperature limit registers?

At power-on, LM90CIMM initializes all temperature limit registers to known defaults: Local and Remote T_CRIT = +85°C, Local and Remote HIGH = +70°C, and Local and Remote LOW = 0°C. These values are loaded automatically before the first conversion completes and remain active until overwritten via SMBus write commands to the respective setpoint registers (03h–08h).