Texas Instruments LM89CIMX

Overview

LM89CIMX from Texas Instruments is an 11-bit remote diode and local digital temperature sensor with SMBus 2.0 interface, ±0.75°C remote accuracy at 30°C/80°C, 3.0–3.6 V supply, and dual open-drain ALERT/T_CRIT_A outputs for thermal monitoring of MCUs, GPUs, FPGAs, and ASICs in computing systems.

For engineers reviewing the LM89CIMX datasheet, LM89CIMX pinout, LM89CIMX application, or LM89CIMX equivalent, this page delivers verified technical context, real-world design meaning for key specs, validated pin functions, confirmed alternative parts with functional distinctions, and supply support for industrial thermal management designs.

Technical Context

The LM89CIMX implements a delta-V_BE-based sensing architecture with separate local silicon and remote diode (e.g., 2N3904 or processor junction) measurement paths. It uses a 10-bit plus sign ADC for remote readings (0.125°C resolution) and 8-bit ADC for local readings (1°C resolution), both updated every 31.25 ms in round-robin sequence.

Its SMBus 2.0 interface supports TIMEOUT reset (25–35 ms low), ALERT masking, and ARA protocol compliance. The device features programmable HIGH/LOW/T_CRIT limit registers, offset compensation for diode nonideality, and independent hysteresis control via TH register affecting both local and remote T_CRIT response.

Key Specifications

Pinout & Package

LM89CIMX is housed in an 8-pin SOIC (D) package measuring 4.9 mm × 3.9 mm, optimized for PCB space-constrained thermal sensing nodes near high-power ICs.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM86CIMM and MAX6657ESA+, the LM89CIMX uniquely delivers ±0.75°C remote accuracy with dual open-drain alarms (ALERT + T_CRIT_A), SMBus 2.0 ARA compliance, and integrated hysteresis control-making it optimal for high-reliability computing thermal shutdown systems requiring minimal host intervention.

Availability

LM89CIMX is available at Aetrix Electronics and suitable for laptop thermal management, server GPU monitoring, FPGA accelerator cards, and industrial PLC controllers requiring stable component supply across extended product lifecycles.

Supply support for LM89CIMX 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 company specializing in analog and embedded processing technologies, with leadership in precision sensing, power management, and interface solutions.

The LM89CIMX belongs to TI's precision temperature sensor product line, designed specifically for high-accuracy thermal monitoring in computing, communications, and industrial systems where die-level temperature awareness prevents performance throttling and hardware failure.

FAQ

What is the remote temperature accuracy specification for LM89CIMX under typical operating conditions?

The LM89CIMX achieves ±0.75°C maximum remote diode temperature accuracy at TA = 30°C and TDiode = 80°C, as specified in the datasheet's Temperature-To-Digital Converter Characteristics table. This accuracy holds for common thermal diodes such as the 2N3904 and Pentium 4–class devices with nonideality factor ~1.0021 and series resistance ≤3.64 Ω. The LM89CIMX achieves this without host software calibration due to its onboard offset register (RTOLB/RTOHB) compensation.

Does LM89CIMX support SMBus Alert Response Address (ARA) protocol, and how is it implemented?

Yes, LM89CIMX fully supports SMBus 2.0 ARA protocol. When the ALERT line is pulled low and the master issues an ARA command, the LM89CIMX responds with its slave address (1001100b for LM89CIMX), then automatically disables the ALERT output by setting the ALERT mask bit (D7) in its Configuration register. This "disengagement" prevents bus lockup and complies with SMBus 2.0 specification requirements - a behavior confirmed in the LM89CIMX functional description and timing diagrams.

What is the purpose of the 2.2 nF capacitor required between D+ and D− pins of LM89CIMX?

The 2.2 nF capacitor between D+ and D− pins of LM89CIMX filters high-frequency noise on the remote diode bias path, ensuring stable delta-V_BE measurements. Per the datasheet layout guidelines, it must be placed as close as possible to both pins with matched trace lengths to minimize parasitic inductance. Omitting or misplacing this capacitor degrades remote accuracy, especially in electrically noisy environments near switching regulators or high-speed digital ICs - a requirement explicitly called out in the LM89CIMX pin function descriptions and layout section.

How does the T_CRIT_A output differ from the ALERT output on LM89CIMX?

The T_CRIT_A output on LM89CIMX is a dedicated, hysteresis-controlled critical alarm that asserts only when local or remote temperature exceeds its respective T_CRIT limit register value. In contrast, ALERT is a general-purpose interrupt that triggers on HIGH, LOW, or T_CRIT limit breaches and supports three configurable modes (comparator, interrupt, or SMBus ARA). Critically, T_CRIT_A remains asserted until temperature falls below (T_CRIT − TH), where TH is the hysteresis register value - a true hardware comparator behavior not replicated by ALERT alone.

Can LM89CIMX measure both local and remote temperatures simultaneously, and what are their respective resolutions?

LM89CIMX measures local and remote temperatures sequentially-not simultaneously-in a round-robin conversion sequence taking 31.25 ms per full cycle. Local temperature resolution is 1°C (8-bit format), while remote temperature resolution is 0.125°C (10-bit plus sign, 11-bit effective). Both values are latched into separate registers (00h–01h for local, 03h–04h for remote) and can be read independently via SMBus at any time, returning the most recent completed conversion result for each channel.