Texas Instruments LM77CIMMX-5/NOPB

Overview

LM77CIMMX-5/NOPB from Texas Instruments is a 9-bit + sign digital temperature sensor and thermal window comparator with I²C interface, ±1.5°C accuracy from −10°C to +65°C, 3.0V–5.5V supply range, and dual open-drain outputs (INT and T_CRIT_A) for programmable over/under-temperature and critical shutdown detection in ACPI-compliant systems.

For engineers reviewing the LM77CIMMX-5/NOPB datasheet, LM77CIMMX-5/NOPB pinout, LM77CIMMX-5/NOPB application, or LM77CIMMX-5/NOPB equivalent, key selection criteria include its default thermal thresholds (TLOW=10°C, THIGH=64°C, T_CRIT=80°C), fault-queue support for noise immunity, shutdown mode (5 μA typ), and compatibility with multi-drop I²C buses up to four devices.

Technical Context

The LM77CIMMX-5/NOPB integrates a band-gap temperature sensor, 10-bit ADC, and digital comparator logic with user-programmable upper (THIGH), lower (TLOW), and critical (T_CRIT) trip points. Hysteresis (THYST) is configurable and applied asymmetrically-added to TLOW and subtracted from THIGH/T_CRIT-to prevent oscillation near thresholds.

It operates in two interrupt modes: Comparator Mode (output resets after each read and reasserts if condition persists) and Event Mode (output latches until next threshold crossing). The INT and T_CRIT_A outputs are independent open-drain signals, each supporting active-low or active-high polarity via configuration register bits.

Key Specifications

Pinout & Package

VSSOP-8 package (DGK0008A), 3.0 mm × 3.0 mm body, 0.65 mm pitch, exposed thermal pad (not electrically connected), RoHS-compliant, lead-free finish.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar digital temperature sensor and thermal window comparator applications.

Compared with MAX31820MUA+ and STTS751DT/R, the LM77CIMMX-5/NOPB uniquely delivers both programmable window comparison and independent critical alarm signaling in hardware-enabling true fail-safe thermal protection without host dependency or bus protocol conversion.

Availability

LM77CIMMX-5/NOPB is available at Aetrix Electronics and suitable for server thermal management, industrial PLC cabinet monitoring, automotive infotainment SoC protection, and HVAC zone sensing requiring stable component supply and long-term manufacturability.

Supply support for LM77CIMMX-5/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 headquartered in Dallas, Texas, delivering analog and embedded processing solutions for industrial, automotive, personal electronics, and communications markets.

The LM77 product line was designed specifically for ACPI-compliant thermal monitoring in PCs and embedded systems, emphasizing autonomous window comparison, dual alarm outputs, and robust noise immunity via configurable fault queue.

FAQ

What is the default power-up behavior of the LM77CIMMX-5/NOPB?

At power-on, the LM77CIMMX-5/NOPB initializes with Comparator Interrupt Mode enabled, TLOW = 10°C, THIGH = 64°C, T_CRIT = 80°C, THYST = 2°C, INT and T_CRIT_A active-low, and pointer register set to the Temperature Register (000b). These defaults comply with ACPI thermal zone initialization requirements and require no initial configuration to begin basic monitoring.

How does the fault queue function in the LM77CIMMX-5/NOPB?

The LM77CIMMX-5/NOPB implements a 4-deep fault queue that requires four consecutive out-of-window temperature readings before asserting INT or T_CRIT_A. This feature is configured via bit D4 of the Configuration Register and significantly improves noise immunity in electrically harsh environments such as motor drives or switch-mode power supplies where transient spikes could otherwise cause false trips.

Can the LM77CIMMX-5/NOPB operate from a 3.3 V supply?

Yes, the LM77CIMMX-5/NOPB operates across 3.0 V to 5.5 V, including standard 3.3 V rails. Its electrical characteristics-including accuracy, conversion time, and I²C timing-are specified at both +5 V and +3.3 V. Accuracy degrades approximately 1°C per volt deviation from nominal supply, so at 3.3 V, expected error remains within ±1.5°C over −10°C to +65°C when calibrated at that voltage.

What is the purpose of the T_CRIT_A output on the LM77CIMMX-5/NOPB?

The T_CRIT_A output on the LM77CIMMX-5/NOPB is a dedicated open-drain hardware alarm signal that activates when temperature exceeds the programmable T_CRIT threshold (default 80°C). Unlike the INT output, it operates independently of host communication and is intended to drive external shutdown circuitry-such as a power supply enable line-ensuring system safety even if the host processor is nonresponsive or locked up.

Does the LM77CIMMX-5/NOPB support multiple devices on a single I²C bus?

Yes, the LM77CIMMX-5/NOPB supports up to four devices on one I²C bus using its two address-select pins (A0 and A1). These pins configure the two least-significant bits of the fixed 7-bit slave address (10010xx), yielding addresses 0x48–0x4B. This multi-drop capability simplifies thermal monitoring across multiple PCB zones without requiring additional I²C ports or bus expanders.