Texas Instruments LM99-1CIMMX/NOPB

Overview

LM99-1CIMMX/NOPB from Texas Instruments is an 11-bit remote diode temperature sensor IC with SMBus 2.0 interface, measuring both local die temperature (±3.0°C max error from 0°C to 85°C) and remote diode junction temperature (±1.0°C max error at 120–140°C), used for GPU/CPU thermal monitoring in graphics cards and server motherboards.

For engineers reviewing the LM99-1CIMMX/NOPB datasheet, LM99-1CIMMX/NOPB pinout, LM99-1CIMMX/NOPB application, or LM99-1CIMMX/NOPB equivalent, key selection criteria include ±1°C remote accuracy over 120–140°C, 0.125°C remote resolution, T_CRIT_A critical alarm output, ALERT interrupt support, and VSSOP-8 package compatibility with thermal diode-connected transistors like 2N3904.

Technical Context

The LM99-1CIMMX/NOPB implements a delta-V_BE-based sensing architecture with a 10-bit plus sign ΔΣ ADC for remote diode measurements and an 8-bit ADC for local temperature. It performs sequential local/remote conversions every 31.25 ms and supports programmable conversion rates via register 04h.

Its SMBus 2.0 slave interface uses fixed 7-bit address 0x4D (1001101), distinct from LM99 (0x4C), enabling coexistence on the same bus. Critical alarm logic drives T_CRIT_A with hysteresis set by TH register, while ALERT operates in comparator, interrupt, or SMBus ARA modes based on FILTER/ALERT CONFIGURE register bit D0.

Key Specifications

Pinout & Package

LM99-1CIMMX/NOPB is housed in an 8-pin VSSOP package (2.3 mm × 2.0 mm, 0.5 mm pitch) with exposed thermal pad for improved heat dissipation in high-density layouts.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM99CIMMX/NOPB, LM99-1CIMMX/NOPB enables dual-sensor deployment on one SMBus; versus MAX6642AESA+, it trades resolution for integrated hardware safety response via T_CRIT_A, reducing firmware dependency in mission-critical thermal shutdown paths.

Availability

LM99-1CIMMX/NOPB is available at Aetrix Electronics and suitable for graphics processor thermal management, computer processor thermal management, and electronic test equipment requiring stable component supply across extended product lifecycles.

Supply support for LM99-1CIMMX/NOPB 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 LM99 family was designed specifically for high-accuracy remote diode thermal monitoring in computing and graphics systems, addressing the need for reliable junction temperature feedback without external calibration components.

FAQ

What is the SMBus slave address of the LM99-1CIMMX/NOPB?

The LM99-1CIMMX/NOPB uses a fixed 7-bit SMBus slave address of 0x4D (1001101). This differs from the LM99 (0x4C), allowing both devices to operate simultaneously on the same SMBus segment without address collision. The address is hardwired and cannot be modified via hardware or software configuration. This feature is explicitly documented in the "SMBus INTERFACE" section of the SNIS129D datasheet.

How does the LM99-1CIMMX/NOPB report remote diode temperature?

The LM99-1CIMMX/NOPB reports remote diode temperature as an 11-bit, two's complement value with 0.125°C LSB, stored left-justified across two 8-bit registers. Critically, the reported value equals the actual diode junction temperature minus 16°C (i.e., T_{LM99-1CIMMX/NOPB} = T_JUNCTION − 16°C), so a reading of +110°C corresponds to 126°C at the diode. This shift is applied internally and is not user-configurable.

Does the LM99-1CIMMX/NOPB support automatic fault detection for the remote diode connection?

Yes, the LM99-1CIMMX/NOPB includes dedicated diode fault detection circuitry that identifies open-circuit, short-to-VDD, or floating conditions on the D+ and D− pins. When a fault is detected, the OPEN bit (D2) in the Status Register (02h) is set, and the remote temperature reading becomes invalid. This behavior is confirmed in the "DIODE FAULT DETECTION" section of the SNIS129D datasheet and requires no external components.

Can the LM99-1CIMMX/NOPB operate with a 3.3 V supply and still meet its accuracy specifications?

Yes, the LM99-1CIMMX/NOPB is fully specified for operation from 3.0 V to 3.6 V, and all accuracy parameters-including ±1.0°C remote diode error at 120–140°C and ±3.0°C local error from 0°C to 85°C-are guaranteed within this range. The 3.3 V nominal supply falls centrally within the operating window and satisfies all electrical characteristics, including quiescent current (0.8 mA typ) and SMBus timing compliance.

What is the function of the Offset Register in the LM99-1CIMMX/NOPB?

The Offset Register (RTOLB and RTOHB) in the LM99-1CIMMX/NOPB compensates for non-ideality errors in different remote diodes-such as variations in series resistance or ideality factor-by applying a programmable correction (±127°C range in 0.125°C steps) to the raw remote temperature reading. This allows accurate matching to discrete diodes (e.g., 2N3904) or ASIC-integrated thermal diodes without hardware trimming.