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Texas Instruments LM81BIMT-3/NOPB
- Part No.:
- LM81BIMT-3/NOPB
- Manufacturer:
- Texas Instruments
- Category:
- Thermal Management
- Package:
- 24-TSSOP (0.173", 4.40mm Width)
- Datasheet:
-
LM81BIMT-3/NOPB.pdf
- Description:
- IC MONITOR SYS HARDWARE 24TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:3,065
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Product details
Overview
LM81BIMT-3/NOPB from Texas Instruments is an ACPI-compatible hardware monitor IC for microprocessor systems, integrating 6-channel voltage monitoring (±1.2% max error), on-die 9-/12-bit temperature sensing (±3°C max), dual fan tachometer inputs, 8-bit DAC for fan speed control (0–1.25 V), and SMBus 1.1 interface - deployed in server thermal management and PC power supply supervision.
For engineers reviewing the LM81BIMT-3/NOPB datasheet, LM81BIMT-3/NOPB pinout, LM81BIMT-3/NOPB application, or LM81BIMT-3/NOPB equivalent, this page delivers verified electrical specs, validated pin functions, confirmed SMBus 1.1 timing compliance, real-world thermal monitoring accuracy, and direct alternatives with documented functional divergence.
Technical Context
The LM81BIMT-3/NOPB implements a dedicated delta-sigma ADC for simultaneous 8-bit conversion of six analog inputs (+12V, +5V, +3.3V, +2.5V, Vccp1, Vccp2) with internal scaling resistors, plus a separate 9-/12-bit two's-complement temperature-to-digital converter with 0.5°C or 0.0625°C LSB resolution. Its fan input circuitry uses Schmitt-trigger digital inputs with programmable divisors (1–4) to support RPM ranges from 1100 to 8800 at full-scale count 255.
It features dual open-drain interrupt outputs (INT and T_CRIT_A), chassis intrusion detection with latch-and-pulse capability (CI pin), VID0–VID4 digital inputs for Pentium/PRO processor voltage identification, and a fully maskable WATCHDOG system comparing all monitored values against user-programmable limits stored in Value RAM (addresses 2Bh–3Ch).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Voltage Monitoring Error | +2% or ±1.2% (max) - ensures reliable detection of out-of-spec supply deviations in server power rails. |
| Temperature Accuracy | ±3°C (−40°C to +125°C) - enables safe thermal throttling and shutdown decisions in high-density computing environments. |
| Supply Voltage Range | 2.8 V to 3.8 V - compatible with standard 3.3 V system rails and tolerant of typical board-level ripple. |
| ADC & DAC Resolution | 8 bits - provides sufficient granularity for voltage/fan feedback loops without excessive bus traffic or processing overhead. |
| Temperature Resolution | 0.5°C (9-bit mode) - balances update rate (0.82 s cycle time) and thermal responsiveness for real-time fan control. |
| SMBus Compatibility | SMBus 1.1 - guarantees interoperability with standard ACPI-compliant host controllers and BIOS implementations. |
| Fan Input Support | 2 Schmitt-trigger inputs with 20 ms–200 ms measurement window - accommodates wide RPM range and slow-rise tach signals from legacy and modern fans. |
Pinout & Package
TSSOP-24 package (TI PW24A), 0.65 mm pitch, 7.8 mm × 4.4 mm footprint, with exposed thermal pad (not electrically connected). Requires low-noise analog ground plane connection at GND (Pin 13) for DAC and ADC performance.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| A0/NTEST_OUT (1) | Address LSB / NAND test output | Configures SMBus slave address (bit 0); asserts during board-level connectivity testing when enabled. |
| A1 (2) | Address MSB | Configures SMBus slave address (bit 1); sets base address to 0x2C–0x2F depending on A0/A1 state. |
| SMBData (3) | SMBus bidirectional data | Open-drain I/O; requires external pull-up; supports standard SMBus read/write protocols per Figure 8–10. |
| SMBCLK (4) | SMBus clock input | Asynchronous master-controlled clock; internal logic operates independently of SMBus timing. |
| FAN1, FAN2 (5–6) | Fan tachometer inputs | Schmitt-trigger digital inputs; accept 0–V+ logic; transition threshold ≈ V+/2; support divisor-based RPM scaling. |
| CI (7) | Chassis intrusion latch input/output | Active-high latch input; internal open-drain output clears intrusion flag via CI Clear Register (46h) with 20 ms pulse. |
| T_CRIT_A (8) | Critical temperature alarm | Active-low open-drain output; dedicated fast-response thermal fault signal independent of INT masking. |
| V+ (9) | Power supply input | +2.8 V to +3.8 V analog/digital supply; bypassed with 10 µF + 0.1 µF capacitors for ADC/DAC stability. |
| INT (10) | Programmable interrupt output | Active-low open-drain; enabled via Bit 1 of Configuration Register (40h); masks individual WATCHDOG sources. |
| DACOut/NTEST_IN (11) | Fan control output / test input | 0–1.25 V analog DAC output; forced high enables NAND Tree test mode for board-level diagnostics. |
| RESET (12) | Master reset output | Active-low open-drain; 20 ms minimum pulse width; enabled by Bit 4 of Configuration Register (40h). |
| GND (13) | Analog/digital ground reference | Common return for all analog inputs, DAC, and internal circuitry; must connect to low-noise analog ground plane. |
| Vccp2 (14) | Negative voltage monitoring input | Analog input scaled externally for −12 V or Vccp2; input resistance 90 kΩ (min); supports offset resistor networks. |
| +12Vin (15) | +12 V supply monitoring input | Direct analog input; accepts −0.05 V to +15 V; internal scaling enables 3/4-scale ADC response at nominal +12 V. |
| +5Vin (16) | +5 V supply monitoring input | Direct analog input; accepts −0.05 V to +6.8 V; used with internal resistor divider for accurate +5 V rail tracking. |
| +3.3Vin (17) | +3.3 V supply monitoring input | Direct analog input; accepts −0.05 V to +4.6 V; optimized for ATX mainboard +3.3 V rail monitoring. |
| +2.5Vin (18) | +2.5 V supply monitoring input | Direct analog input; accepts −0.05 V to +3.6 V; supports core logic and memory voltage supervision. |
| Vccp1 (19) | Processor core voltage input | Analog input for Vccp (nominally +2.5 V); used with VID0–VID4 to track dynamic CPU voltage scaling. |
| VID4–VID0 (20–24) | Processor VID code inputs | Digital inputs capturing Pentium/PRO VID codes (1.5 V–2.9 V); values read into VID/Fan Divisor Register (47h) and VID4 Register (49h). |
Key Features
| Feature | Design Value |
|---|---|
| Integrated 6-channel voltage monitoring | Eliminates need for external scaling resistors on +12V, +5V, +3.3V, +2.5V, Vccp1, Vccp2 - reduces BOM count and layout area. |
| On-chip temperature sensor with selectable resolution | 9-bit (0.5°C) or 12-bit (0.0625°C) mode - allows trade-off between thermal update latency (0.82 s vs. 1.2 s) and precision. |
| Programmable fan speed control DAC | 0–1.25 V output drives standard PWM fan controllers or linear fan drivers - enables closed-loop thermal management without MCU intervention. |
| Dual independent fan tachometer inputs | Supports simultaneous monitoring of CPU and chassis fans with configurable divisors - simplifies multi-fan thermal profiles in servers. |
| Chassis intrusion detection with latched event | CI pin captures physical tampering events even during power loss - meets enterprise security requirements for unattended systems. |
| WATCHDOG comparison across all monitored parameters | Hardware compares temperature, voltages, and fan speeds against user-defined thresholds - triggers interrupts before system failure occurs. |
Applications
| Server Thermal Management | PC Power Supply Supervision |
|---|---|
|
Use Scenario: Real-time monitoring of CPU die temperature, VRM output voltages (+12V, +5V, +3.3V), and dual cooling fans in 1U/2U rack servers. IC Role / Device Role / Timing Role: Hardware monitor IC performing autonomous round-robin acquisition every ~400 ms, triggering T_CRIT_A within <100 µs on critical overtemperature. Use Value: Enables BIOS-independent thermal shutdown and fan speed ramping - prevents CPU damage during sustained load or airflow blockage. |
Use Scenario: Supervising ATX power supply rails (+3.3V, +5V, +12V), motherboard Vccp, and chassis fan in desktop PCs with ACPI-compliant firmware. IC Role / Device Role / Timing Role: SMBus 1.1 slave providing voltage/temperature/fan status to host controller; supports SMI-based thermal throttling. Use Value: Delivers deterministic watchdog response and VID decoding for dynamic CPU voltage scaling - improves system stability under variable workloads. |
| Office Electronics Monitoring | Electronic Test Equipment |
|
Use Scenario: Monitoring power integrity and thermal margins in network-attached storage (NAS) enclosures with dual hot-swap fans and multiple DC-DC converters. IC Role / Device Role / Timing Role: Centralized analog/digital acquisition node feeding health data to embedded ARM controller via SMBus. Use Value: Reduces firmware complexity by offloading voltage/temp/fan polling - frees MCU cycles for RAID management and network stack. |
Use Scenario: Embedded thermal and supply monitoring in benchtop oscilloscopes and spectrum analyzers requiring long-term calibration stability. IC Role / Device Role / Timing Role: Precision analog front-end with ±3°C temp accuracy and ±1.2% voltage error - maintains measurement integrity across ambient range. Use Value: Eliminates need for external temperature sensors and voltage references - lowers cost and improves MTBF in sealed instrument enclosures. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar hardware monitoring applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LM87CIMT-3/NOPB | Includes remote diode temperature sensing (vs. on-die only), higher voltage monitoring accuracy (±0.8%), and integrated 10-bit ADC. | Required for systems needing CPU die + motherboard ambient temperature correlation; supports more complex thermal profiles. | Select when dual-point thermal mapping or tighter voltage tolerance is mandatory; not drop-in due to different register map and pinout. |
| ADM1027ASTZ-REEL | Features 3-zone thermal monitoring (on-die + 2 remote diodes), SMBus 2.0, and enhanced fan control with automatic PWM generation. | Targeted at high-end servers with multi-socket CPUs and liquid-cooled modules requiring granular zone-based fan control. | Choose for advanced thermal zoning and protocol compatibility with newer platform controllers; requires PCB redesign and firmware updates. |
Compared with LM81BIMT-3/NOPB, LM87CIMT-3/NOPB adds remote diode support but increases complexity and cost, while ADM1027ASTZ-REEL offers superior thermal zoning and SMBus 2.0 but lacks pin compatibility and demands full system revalidation.
Availability
LM81BIMT-3/NOPB is available at Aetrix Electronics and suitable for server thermal management, PC power supply supervision, office electronics monitoring, and electronic test equipment requiring stable component supply across extended product lifecycles.
Supply support for LM81BIMT-3/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 leader specializing in analog, embedded processing, and connectivity technologies, with decades of heritage in precision data acquisition and system monitoring ICs.
The LM81 family was designed specifically for ACPI-compliant hardware monitoring in x86-based computing platforms - delivering integrated voltage, temperature, fan, and intrusion sensing in a single TSSOP package for space-constrained server and desktop motherboards.
FAQ
What is the SMBus interface version supported by LM81BIMT-3/NOPB?
The LM81BIMT-3/NOPB implements SMBus 1.1 interface compliance, as explicitly stated in its datasheet revision (February 2002). This ensures full interoperability with ACPI-compliant host controllers and BIOS implementations common in Pentium II/III-era servers and desktops. It does not support SMBus 2.0 features such as packet error checking or alert response protocol.
Does LM81BIMT-3/NOPB support remote temperature sensing via external diodes?
No, LM81BIMT-3/NOPB does not support remote diode temperature sensing. It contains only an on-die temperature sensor with ±3°C accuracy over −40°C to +125°C. Remote diode capability is found in later TI parts like LM87CIMT-3/NOPB, but is absent in the LM81BIMT-3/NOPB silicon design and register set.
What is the maximum fan RPM measurable by LM81BIMT-3/NOPB with default settings?
With default fan divisor = 1 and full-scale count = 255, LM81BIMT-3/NOPB measures up to 8800 RPM on FAN1 or FAN2 inputs when the tachometer pulse count equals 153. This value scales inversely with divisor setting: 4400 RPM at divisor = 2, 2200 RPM at divisor = 3, and 1100 RPM at divisor = 4 - enabling flexible matching to diverse fan types.
Can LM81BIMT-3/NOPB monitor negative supply voltages like −12V?
Yes, LM81BIMT-3/NOPB can monitor −12V using the Vccp2 analog input pin (Pin 14) with an external resistor divider network. The datasheet specifies that Vccp2 accepts input voltages scaled to +2.5V, allowing bidirectional translation of negative rails. No internal circuitry supports direct −12V connection - external scaling is mandatory and referenced to GND.
What is the function of the DACOut/NTEST_IN pin (Pin 11) on LM81BIMT-3/NOPB?
Pin 11 (DACOut/NTEST_IN) serves dual roles: as an 8-bit DAC output delivering 0–1.25 V for fan speed control, and as a NAND Tree test input. When externally driven high, it activates board-level connectivity testing mode - a diagnostic feature used during manufacturing to verify solder joints and trace continuity without requiring functional operation of the LM81BIMT-3/NOPB.
LM81BIMT-3/NOPB Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- -
- Package/Case:
- 24-TSSOP (0.173", 4.40mm Width)
- Packaging:
- Tube
- Product Status:
- Obsolete
- Function:
- Hardware Monitor
- Sensor Type:
- Internal and External
- Sensing Temperature:
- -40°C ~ 125°C
- Accuracy:
- ±3°C(Max)
- Topology:
- ADC (Sigma Delta), Comparator, Fan Speed Control, Register Bank
- Output Type:
- 2-Wire SMBus
- Output Alarm:
- Yes
- Output Fan:
- Yes
- Voltage - Supply:
- 2.8V ~ 3.8V
- Operating Temperature:
- -40°C ~ 125°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 24-TSSOP
LM81BIMT-3/NOPB FAQ
1.How can I place an order for LM81BIMT-3/NOPB through Aetrix?
Please submit a Request for Quotation (RFQ) for LM81BIMT-3/NOPB on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for LM81BIMT-3/NOPB reliable?
The price and inventory of LM81BIMT-3/NOPB are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LM81BIMT-3/NOPB is usually 5 days.
3.What payment methods are accepted for LM81BIMT-3/NOPB?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LM81BIMT-3/NOPB transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LM81BIMT-3/NOPB?
LM81BIMT-3/NOPB orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LM81BIMT-3/NOPB order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for LM81BIMT-3/NOPB?
For technical support, including LM81BIMT-3/NOPB datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LM81BIMT-3/NOPB requirements.
6.How does Aetrix verify that LM81BIMT-3/NOPB is sourced from the original manufacturer or authorized distributors?
All LM81BIMT-3/NOPB products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that LM81BIMT-3/NOPB meets industry standards.
7.What is the process for return or replacement of LM81BIMT-3/NOPB?
All LM81BIMT-3/NOPB units undergo pre-shipment inspection (PSI). If there is an issue with LM81BIMT-3/NOPB, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The LM81BIMT-3/NOPB part is unused and in its original packaging.
Return procedure for LM81BIMT-3/NOPB:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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