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Texas Instruments LM81BIMTX-3
- Part No.:
- LM81BIMTX-3
- Manufacturer:
- Texas Instruments
- Category:
- Thermal Management
- Package:
- 24-TSSOP (0.173", 4.40mm Width)
- Datasheet:
-
LM81BIMTX-3.pdf
- Description:
- IC MPU SYSTEM HDWR MON 24-TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:4,389
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Product details
Overview
LM81BIMTX-3 from Texas Instruments is an SMBus 1.1–compliant hardware monitor IC for x86-based systems, integrating a 9-/12-bit temperature sensor, six analog voltage inputs (+12V, +5V, +3.3V, +2.5V, Vccp1, Vccp2), two fan tachometer inputs, an 8-bit DAC (0–1.25 V), and chassis intrusion detection. It delivers ±3°C temperature accuracy over −40°C to +125°C and ±1.2% max voltage monitoring error in server and desktop thermal/power management.
For engineers reviewing the LM81BIMTX-3 datasheet, LM81BIMTX-3 pinout, LM81BIMTX-3 application, or LM81BIMTX-3 equivalent, this page provides verified technical context, real-world design meaning of key specs, validated pin functions, confirmed alternative parts with documented differences, and supply support for industrial embedded and OEM deployment.
Technical Context
The LM81BIMTX-3 implements a delta-sigma ADC architecture for simultaneous 8-bit conversion of six analog inputs and on-die temperature sensing, with programmable watchdog limits per monitored channel. Its SMBus 1.1 interface supports slave-only operation at up to 100 kHz, using open-drain SMBCLK/SMBData lines and address pins A0/A1 for configurable device addressing.
It features dual interrupt outputs (INT and T_CRIT_A), where T_CRIT_A is dedicated to critical overtemperature events with independent enable control via Extended Mode Register 1, while INT is fully maskable per source. Fan speed measurement uses Schmitt-trigger inputs with programmable divisors (1–4) and full-scale count of 255, supporting nominal speeds from 1100 to 8800 RPM.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Voltage Monitoring Error | ±1.2% (max) - ensures reliable detection of out-of-spec supply deviations in +12V/+5V/+3.3V/+2.5V/Vccp rails without false alarms. |
| Temperature Accuracy | ±3°C (−40°C to +125°C) - enables robust thermal throttling and shutdown decisions in server chassis and CPU VRM environments. |
| DAC Output Range | 0 V to +1.25 V - directly interfaces with standard PWM fan controllers requiring analog voltage input for closed-loop speed regulation. |
| Fan Input Type | Schmitt-trigger digital inputs - tolerates slow-rising tachometer signals from brushless DC fans and rejects noise in high-noise PC chassis. |
| SMBus Compatibility | SMBus 1.1 - guarantees interoperability with ACPI-compliant host controllers and BIOS firmware stacks in legacy and modern x86 platforms. |
| Supply Voltage Range | +2.8 V to +3.8 V - matches standard +3.3 V system rail with ±10% tolerance, eliminating need for external LDO in most motherboard designs. |
| Operating Temperature | −40°C to +125°C - supports placement near CPU VRMs, GPU power stages, and other high-heat zones in industrial PCs and servers. |
Pinout & Package
TSSOP-24 package (TI PW24A), 7.8 mm × 4.4 mm, 0.65 mm pitch, thermally enhanced with exposed pad (GND-connected).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| A0/NTEST_OUT | Address LSB / NAND test output | Configures SMBus address bit 0; doubles as board-level connectivity test output during manufacturing. |
| A1 | Address MSB | Configures SMBus address bit 1; enables up to four LM81BIMTX-3 devices on same bus without conflict. |
| SMBData | SMBus bidirectional data | Open-drain I/O requiring external pull-up; carries all register reads/writes and status updates per SMBus 1.1 protocol. |
| SMBCLK | SMBus clock input | Asynchronous master-driven clock; internal ADC/fan timing runs independently, ensuring monitoring continuity during bus stalls. |
| FAN1, FAN2 | Fan tachometer inputs | Schmitt-trigger digital inputs accepting 0–V+ logic; support divisor programming for accurate RPM scaling across fan types. |
| CI | Chassis intrusion latch input/output | Accepts active-high intrusion signal; also provides open-drain reset pulse (20 ms min) to clear external intrusion latches. |
| T_CRIT_A | Critical temperature alarm | Active-low open-drain output dedicated to thermal runaway response-bypasses INT masking for fastest possible shutdown. |
| V+ | Power supply input | +2.8 V to +3.8 V analog/digital core supply; requires parallel 10 µF + 0.1 µF bypassing for stable ADC/DAC performance. |
| INT | Programmable interrupt output | Active-low open-drain output; individually maskable per monitored parameter (voltage, temp, fan, intrusion) in Configuration Register. |
| DACOut/NTEST_IN | DAC analog output / test mode entry | Delivers 0–1.25 V fan control voltage; forced high enables NAND tree test mode for production board validation. |
| RESET | Open-drain reset output | 20 ms minimum active-low pulse triggered by Configuration Register Bit 4; used for system-wide power-on reset coordination. |
| GND | Analog/digital ground reference | Single-point connection for all analog inputs and DAC output; must tie to low-noise analog ground plane to maintain ±1.2% voltage accuracy. |
| +12Vin to +2.5Vin, Vccp1, Vccp2 | Analog voltage monitoring inputs | High-impedance (≥90 kΩ) inputs scaled via external resistors; support direct monitoring of +12V, +5V, +3.3V, +2.5V, and processor Vccp rails. |
| VID4–VID0 | Pentium/PRO VID code inputs | Digital inputs capturing CPU core voltage selection bits (1.5 V–2.9 V range); read into VID/Fan Divisor Register for dynamic voltage tracking. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated delta-sigma ADC | Simultaneously digitizes six power rails and die temperature with 8-bit resolution-eliminates need for external ADC and reduces BOM count. |
| Programmable watchdog engine | Per-channel upper/lower limits stored in Value RAM (addresses 2Bh–3Ch); triggers masked/unmasked interrupts on violation without host CPU intervention. |
| Dual interrupt architecture | T_CRIT_A provides hardware-fast thermal emergency response (<10 µs latency), while INT supports flexible software-configurable alert prioritization and logging. |
| VID voltage code capture | Direct sampling of Pentium/PRO VID0–VID4 lines enables real-time correlation between CPU voltage state and Vccp rail measurements for adaptive power management. |
| NAND tree test mode | Enabled via DACOut/NTEST_IN high or A0/NTEST_OUT output-validates PCB interconnect integrity during board test without firmware involvement. |
Applications
| Server Thermal Management | Desktop Power Integrity Monitoring |
|---|---|
|
Use Scenario: Real-time monitoring of CPU VRM output (Vccp1), +12V PSU rail, and heatsink temperature in 1U rack servers. IC Role / Device Role / Timing Role: Hardware monitor providing autonomous watchdog-triggered thermal throttling and voltage fault reporting via SMBus to BMC. Use Value: Enables fail-safe operation under sustained load; ±3°C temp accuracy and ±1.2% voltage error prevent premature shutdown or undetected brownouts. |
Use Scenario: Simultaneous tracking of +3.3V, +5V, and +12V motherboard rails alongside CPU core voltage (Vccp1) and fan speeds in consumer desktops. IC Role / Device Role / Timing Role: Centralized acquisition node feeding voltage/temp/fan data to BIOS for ACPI-compliant power states and fan curve control. Use Value: Reduces firmware complexity by offloading analog sensing and interrupt generation; SMBus 1.1 compatibility ensures plug-and-play integration with legacy chipset drivers. |
| Industrial PC Environmental Control | Embedded System Chassis Security |
|
Use Scenario: Monitoring ambient temperature, +24V field power supply, and cooling fan RPM in fanless industrial PCs deployed in factory automation cabinets. IC Role / Device Role / Timing Role: Standalone environmental supervisor operating across −40°C to +125°C junction range, with DAC-controlled fan speed adaptation. Use Value: Maintains system uptime in wide-temperature environments; 0–1.25 V DAC output drives common 0–5 V fan controllers without level-shifting circuitry. |
Use Scenario: Detecting unauthorized physical access to sealed medical or military computing enclosures via chassis intrusion switch. IC Role / Device Role / Timing Role: Intrusion event latching and reporting through CI pin, with hardware-clear capability via CI Clear Register (46h). Use Value: Provides tamper-evident logging independent of host OS; active-high CI input works regardless of LM81 power state, ensuring detection even during deep sleep. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar hardware monitoring applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LM81CIMTX-3 | SMBus 1.0 compatible; voltage monitoring accuracy ±2% (vs. ±1.2% for LM81BIMTX-3); no VID4 input support. | Limited to legacy ACPI 1.0 platforms; lacks Pentium/PRO VID voltage tracking required for dynamic CPU voltage scaling. | Select LM81CIMTX-3 only for cost-sensitive, non-VID applications where SMBus 1.0 suffices and tighter voltage tolerance is not required. |
| ADM1027ASTZ-REEL | Higher temp accuracy (±1°C), integrated remote diode sensing, but no VID inputs; operates from 3.0–3.6 V only. | Supports dual-diode thermal monitoring for CPU/GPU; lacks native chassis intrusion input and SMBus 1.1 compliance. | Choose ADM1027ASTZ-REEL when remote diode sensing and sub-±2°C accuracy are mandatory, and chassis intrusion is handled externally. |
Compared with LM81CIMTX-3, the LM81BIMTX-3 offers tighter voltage monitoring and SMBus 1.1 readiness for modern BIOS; versus ADM1027ASTZ-REEL, it provides VID support and intrusion detection at the cost of reduced thermal accuracy and no remote diode interface.
Availability
LM81BIMTX-3 is available at Aetrix Electronics and suitable for server thermal management, desktop power integrity monitoring, industrial PC environmental control, and embedded system chassis security requiring stable component supply across extended temperature and long-lifecycle deployments.
Supply support for LM81BIMTX-3 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 product line was designed specifically for ACPI-compliant hardware monitoring in x86-based computing platforms, delivering integrated voltage, temperature, fan, and security sensing in a single TSSOP package for motherboard and server OEMs.
FAQ
What is the SMBus compatibility of the LM81BIMTX-3?
The LM81BIMTX-3 implements full SMBus 1.1 compliance, including timeout detection (35 ms max), packet error checking, and alert response protocol. It operates as a slave-only device with configurable 7-bit address via A0/A1 pins, and supports standard read/write operations to its internal register map-including Value RAM, Configuration Register (40h), and Extended Mode Registers (4Ch/4Dh). This ensures seamless integration with ACPI-compliant host controllers in both legacy and modern BIOS implementations.
How does the LM81BIMTX-3 handle chassis intrusion detection?
The LM81BIMTX-3 provides dedicated chassis intrusion support via the CI pin, which accepts an active-high signal from an external mechanical switch. Once asserted, the event is latched and reported in the Interrupt Status Registers. The CI pin also functions as an open-drain output: writing to the CI Clear Register (46h) generates a precise 20 ms minimum low pulse to reset external intrusion latches-enabling full hardware-level tamper detection and recovery without host CPU involvement.
What is the function of the DACOut/NTEST_IN pin on the LM81BIMTX-3?
The DACOut/NTEST_IN pin serves dual roles: as an 8-bit DAC output delivering 0 V to +1.25 V for analog fan speed control, and as a test-mode entry point. When driven high externally (≥2.0 V), it activates NAND Tree Test mode, enabling board-level connectivity verification during manufacturing. In normal operation, DAC output resolution is 8 bits (4.88 mV/LSB), with ±5% max error at V+ = 3.3 V, making it suitable for closed-loop thermal management in PCs and servers.
Does the LM81BIMTX-3 support monitoring of negative supply voltages like −12V?
Yes-the LM81BIMTX-3 supports −12V monitoring via the Vccp2 analog input. An external resistor divider scales the negative voltage to a positive range within the LM81BIMTX-3's input specification (−0.05 V to +3.6 V for Vccp2). TI recommends using matched resistors to minimize offset error, and the input exhibits ≥90 kΩ impedance, ensuring minimal loading on the source. This capability enables full rail coverage-including +12V, +5V, +3.3V, +2.5V, Vccp1, and −12V-in a single IC.
What is the temperature resolution and conversion time of the LM81BIMTX-3?
The LM81BIMTX-3 offers selectable temperature resolution: 9-bit mode (0.5°C LSB, 50 ms typical conversion) and 12-bit mode (0.0625°C LSB, 400 ms typical conversion). Resolution is configured via the Temperature Configuration Register (4Bh) and Extended Mode Registers (4Ch/4Dh). Total monitoring cycle time-including all six voltage inputs, temperature, and two fan readings-is 400 ms in default 9-bit mode, enabling responsive thermal management while maintaining low average current (0.4 mA typ).
LM81BIMTX-3 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- -
- Package/Case:
- 24-TSSOP (0.173", 4.40mm Width)
- Packaging:
- Tape & Reel (TR)
- 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
LM81BIMTX-3 FAQ
1.How can I place an order for LM81BIMTX-3 through Aetrix?
Please submit a Request for Quotation (RFQ) for LM81BIMTX-3 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 LM81BIMTX-3 reliable?
The price and inventory of LM81BIMTX-3 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LM81BIMTX-3 is usually 5 days.
3.What payment methods are accepted for LM81BIMTX-3?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LM81BIMTX-3 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LM81BIMTX-3?
LM81BIMTX-3 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LM81BIMTX-3 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 LM81BIMTX-3?
For technical support, including LM81BIMTX-3 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LM81BIMTX-3 requirements.
6.How does Aetrix verify that LM81BIMTX-3 is sourced from the original manufacturer or authorized distributors?
All LM81BIMTX-3 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 LM81BIMTX-3 meets industry standards.
7.What is the process for return or replacement of LM81BIMTX-3?
All LM81BIMTX-3 units undergo pre-shipment inspection (PSI). If there is an issue with LM81BIMTX-3, 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 LM81BIMTX-3 part is unused and in its original packaging.
Return procedure for LM81BIMTX-3:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
LM81BIMTX-3 Tags
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EMC2101-ACZL-TR
Microchip Technology
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MCP9844T-BE/MNY
Microchip Technology
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EMC2101-R-ACZL-TR
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AMC6821SDBQR
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MAX6604AATA+T
Analog Devices Inc./Maxim Integrated
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ADT7475ARQZ-REEL
onsemi
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MAX6643LBBAEE+
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MAX6684ESA+T
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MAX6639AEE+
Analog Devices Inc./Maxim Integrated
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