Texas Instruments LM84BIMQAX/NOPB

Overview

LM84BIMQAX/NOPB from Texas Instruments (formerly National Semiconductor) is a diode-input digital temperature sensor with SMBus/I²C interface, designed for dual-point thermal monitoring - measuring both its own local die temperature and the remote junction temperature of a semiconductor diode (e.g., Pentium II processor or 2N3904-based discrete diode). It features ±1.0°C local accuracy, ±3°C remote accuracy over +60°C to +100°C, programmable T_CRIT alarm output, and operates from 3.0V–3.6V supply. It is used in PC motherboard thermal management and embedded system overtemperature protection.

For engineers reviewing the LM84BIMQAX/NOPB datasheet, LM84BIMQAX/NOPB pinout, LM84BIMQAX/NOPB application, or LM84BIMQAX/NOPB equivalent, key selection considerations include remote diode sensing capability, SMBus timeout support, open-drain T_CRIT_A interrupt behavior, 8-bit two's complement temperature data format, and QSOP-16 package compatibility with high-density PCB layouts.

Technical Context

The LM84BIMQAX/NOPB integrates a Delta-Sigma ADC, bandgap-based local temperature sensor, and precision current source/sink for remote diode biasing. It alternates sampling between local and remote channels every ~60 ms, updating the T_CRIT_A output and Status Register upon conversion completion.

Its SMBus slave interface uses hardwired A3=1 and user-configurable ADD0/ADD1 pins to select among nine unique 7-bit addresses. The device supports SMBus timeout reset (≥40 ms low on SMBCLK or SMBData), open-drain SMBData/T_CRIT_A outputs requiring external pull-ups, and fault detection for open/shorted remote diodes via Status Register bit D2 (OPEN).

Key Specifications

Pinout & Package

LM84BIMQAX/NOPB is housed in a 16-pin QSOP (SSOP-DBQ) package with 0.635 mm pitch and exposed pad not electrically connected. Thermal resistance (junction-to-ambient) is unspecified but optimized for PCB-mounted operation with 2 oz copper.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar diode-input digital temperature sensor applications.

Compared with LM84BIMQAX/NOPB, LM94022QDCNT/NOPB offers superior remote accuracy and lower supply voltage flexibility but omits SMBus timeout recovery; MAX6642AESA+ provides simpler I²C integration but reduces multi-drop bus capacity and removes programmable T_CRIT masking.

Availability

LM84BIMQAX/NOPB is available at Aetrix Electronics and suitable for PC motherboard thermal management, industrial embedded controllers, and office equipment safety systems requiring stable component supply and long-term lifecycle continuity.

Supply support for LM84BIMQAX/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 acquired National Semiconductor in 2011 and maintains full technical and manufacturing continuity for legacy analog products including the LM84 series.

The LM84BIMQAX/NOPB belongs to TI's precision analog temperature sensor product line, engineered specifically for dual-point thermal monitoring in computing and industrial platforms where SMBus integration and hardware-level thermal interrupts are essential.

FAQ

What is the remote diode sensing accuracy of the LM84BIMQAX/NOPB across its full operating range?

The LM84BIMQAX/NOPB achieves ±3°C (max) remote temperature accuracy from +60°C to +100°C when used with a Pentium II processor diode or 2N3904-connected discrete diode. Outside that range - from 0°C to +125°C - accuracy degrades to ±5°C (max). This specification assumes proper PCB layout per Application Note DS100961, including matched D+/D− traces and guard ring grounding. Accuracy does not include additional error from diode non-ideality factor variation.

How does the T_CRIT_A output behave when both local and remote temperatures exceed their respective critical thresholds?

The T_CRIT_A output of the LM84BIMQAX/NOPB asserts (goes low) if either the local temperature exceeds LT_CRIT or the remote temperature exceeds RT_CRIT. After assertion, the Status Register (address 02h) must be read to determine which condition caused the alarm: bit D6 (LTCRIT) indicates local overtemperature; bit D4 (RTCRIT) indicates remote overtemperature. Reading the Status Register clears both flags and releases T_CRIT_A only if temperatures have fallen below their thresholds.

Can the LM84BIMQAX/NOPB operate with a 5V SMBus controller?

No - the LM84BIMQAX/NOPB is not 5V-tolerant. Its SMBData and SMBCLK pins accept only 3.0V–3.6V logic levels (VIL ≤0.6 V, VIH ≥2.1 V at VCC = 3.3 V). Interfacing with a 5V SMBus controller requires level-shifting circuitry, such as a dual-supply bidirectional translator (e.g., TXS0102), to avoid exceeding absolute maximum ratings and damaging the device.

What happens during power-up, and what are the default register values of the LM84BIMQAX/NOPB?

At power-up, the LM84BIMQAX/NOPB initializes with Local Temperature = 0°C, Remote Temperature = 0°C (until diode presence is confirmed), Status Register = 00h, Command Register = 00h (pointing to Read Local Temp), and both LT_CRIT and RT_CRIT registers = +127°C. The T_CRIT_A output is enabled by default (Configuration Register D7 = 0), and ADD0/ADD1 pin states are latched on the first SMBus transaction to set the slave address.

Is the LM84BIMQAX/NOPB RoHS compliant and lead-free?

Yes - the LM84BIMQAX/NOPB is RoHS compliant and features a lead-free NIPDAU (nickel-palladium-gold) or pure tin (SN) lead finish, depending on date code. It carries MSL Level-1 rating (unlimited floor life at ≤30°C/60% RH) and is qualified for peak reflow temperatures up to 260°C, meeting JEDEC J-STD-020 standards for lead-free assembly.