Texas Instruments LM89-1CIM/NOPB

Overview

LM89-1CIM/NOPB 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 LM89-1CIM/NOPB datasheet, LM89-1CIM/NOPB pinout, LM89-1CIM/NOPB application, or LM89-1CIM/NOPB equivalent, key selection considerations include remote diode measurement resolution (0.125°C), local T_CRIT default threshold (85°C), SMBus timeout reset behavior, D+/D− noise filtering requirements (2.2 nF capacitor), and compatibility with LM86/LM90 register maps.

Technical Context

The LM89-1CIM/NOPB implements a delta-V_BE-based sensing architecture with separate 10-bit-plus-sign remote and 8-bit local ADCs. It supports programmable conversion rates (31.25 ms base time), configurable hysteresis via TH register, and three ALERT operating modes: comparator, interrupt flag, and SMBus ARA protocol responder.

Its SMBus 2.0 interface complies with TIMEOUT reset (25–35 ms low-time), tHD;DAT (300–900 ns), and f_SMB (10–100 kHz) specifications. The device uses dedicated D+ (current source) and D− (current sink) terminals for remote diode biasing, with internal nonideality compensation via RTOLB/RTOHB offset registers.

Key Specifications

Pinout & Package

LM89-1CIM/NOPB is housed in an 8-pin VSSOP (DGK) package, 3.0 mm × 3.0 mm body size, with exposed pad for thermal performance. Pin functions are validated per TI SNIS128D Rev D (June 2014).

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM89-1CIM/NOPB, LM86CIM/NOPB sacrifices critical-alarm hardware autonomy and remote accuracy for lower unit cost, while MAX6657ESA+ trades SMBus 2.0 features and precision for broader legacy ecosystem support - making LM89-1CIM/NOPB optimal for new designs requiring deterministic thermal shutdown.

Availability

LM89-1CIM/NOPB is available at Aetrix Electronics and suitable for laptop thermal management, server blade monitoring, and industrial FPGA thermal guard applications requiring stable component supply, long-term lifecycle assurance, and traceable sourcing.

Supply support for LM89-1CIM/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, and communications markets since 1930.

The LM89 product line was designed specifically for high-accuracy, SMBus-based thermal monitoring in space-constrained computing platforms - targeting CPU, GPU, and ASIC die temperature measurement with minimal external components.

FAQ

What is the default local T_CRIT temperature setting for LM89-1CIM/NOPB?

The LM89-1CIM/NOPB has a default local T_CRIT temperature setting of 85°C at power-up, as specified in the Device Comparison Table of the SNIS128D datasheet. This value is stored in the local T_CRIT limit register (address 20h) and can be reprogrammed via SMBus. The LM89-1DIMM variant defaults to 105°C, but LM89-1CIM/NOPB strictly uses 85°C unless modified by host firmware. This setting directly controls the activation threshold of the T_CRIT_A output pin.

How does the 2.2 nF capacitor requirement affect LM89-1CIM/NOPB layout?

The LM89-1CIM/NOPB requires a 2.2 nF capacitor placed as close as possible between the D+ and D− pins to filter high-frequency noise from the remote diode path. Per Section 7 of SNIS128D, mismatched trace lengths to this capacitor degrade measurement stability, and placement >2 mm from either pin increases susceptibility to EMI-induced errors. This capacitor is mandatory for achieving the ±0.75°C remote accuracy specification - omitting it or using incorrect value/size results in uncalibrated drift exceeding ±3°C in noisy environments.

Is LM89-1CIM/NOPB compatible with SMBus 2.0 TIMEOUT reset functionality?

Yes, LM89-1CIM/NOPB fully supports SMBus 2.0 TIMEOUT reset: holding SMBData and/or SMBCLK low for 25–35 ms resets the internal SMBus state machine and places both lines in high-impedance mode. This behavior is verified in Section 8.8 of SNIS128D and enables robust bus recovery after communication faults. Unlike SMBus 1.1 devices, LM89-1CIM/NOPB guarantees deterministic reset without requiring power cycle - critical for unattended server and telecom equipment where bus lockup must be self-correcting.

What remote diode nonideality factors can be compensated using LM89-1CIM/NOPB's offset registers?

The LM89-1CIM/NOPB uses RTOLB and RTOHB offset registers to compensate for diode nonideality factors such as ideality factor deviation (e.g., 1.0021 for Pentium 4), series resistance (e.g., 3.64 Ω), and process variation across different IC dies. These 8-bit registers allow ±127°C adjustment in 1°C steps, enabling calibration against known reference temperatures without host software recalculating raw ADC values. This compensation is applied automatically in hardware before temperature register updates, ensuring all reads from the remote temperature register reflect corrected values.

Does LM89-1CIM/NOPB support SMBus Alert Response Address (ARA) protocol?

Yes, LM89-1CIM/NOPB fully supports SMBus 2.0 ARA protocol: when the ALERT line is pulled low and the master issues an ARA command, the device transmits its slave address (1001101b for LM89-1C), then disables ALERT output by setting the ALERT mask bit (D7 of Configuration register) to prevent bus contention. This behavior is documented in Section 9.3.2.3 of SNIS128D and ensures interoperability with multi-device SMBus alert networks - unlike many competing sensors that lack true ARA compliance or require external glue logic.