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Texas Instruments LM87CIMT
- Part No.:
- LM87CIMT
- Manufacturer:
- Texas Instruments
- Category:
- Thermal Management
- Package:
- 24-TSSOP (0.173", 4.40mm Width)
- Datasheet:
-
LM87CIMT.pdf
- Description:
- IC MONITOR SYS HARDWARE 24TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:317
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Product details
Overview
LM87CIMT from Texas Instruments is a highly integrated hardware monitor IC for server, workstation, and PC motherboard thermal and power management. It provides remote diode temperature sensing (2 channels), 8 positive voltage inputs with internal scaling resistors (+5 V, +12 V, +3.3 V, +2.5 V, Vccp1, Vccp2), dual fan speed monitoring/counting, an 8-bit DAC for fan control, chassis intrusion detection, and SMBus/I²C interface compatibility - all in a single 24-pin TSSOP package.
For engineers reviewing the LM87CIMT datasheet, LM87CIMT pinout, LM87CIMT application, or LM87CIMT equivalent, this device serves as a system-level sensor hub for real-time voltage, temperature, and fan RPM telemetry in x86-based computing platforms requiring watchdog-triggered interrupt signaling (INT# and THERM#) and VID/IRQ monitoring for processor voltage identification.
Technical Context
The LM87CIMT integrates a slow-speed ΣΔ ADC for stable measurement in noisy environments, supporting simultaneous conversion of internal junction temperature, two external diode temperatures (e.g., Pentium/PRO diodes), and eight analog voltage inputs. Its dual-function pins (VID0–VID4, FAN1/AIN1, FAN2/AIN2) enable flexible configuration between voltage monitoring and digital tachometer input modes via the Channel Mode Register.
It implements programmable hardware watchdog limits across all monitored parameters, with independent masking and status mirroring for INT# and THERM# outputs. The 8-bit DAC (0–2.5 V output) drives fan PWM circuits directly, while the SMBus-compatible serial interface operates at up to 400 kHz with timeout recovery and address selection via the ADD pin (01011XY binary).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Voltage Monitoring Error | ±2 % (max) - ensures accurate power rail validation for +12 V, +5 V, +3.3 V, +2.5 V, Vccp1, Vccp2 without external scaling components. |
| Internal Temp Accuracy | ±3 °C (typ, −40 °C to +125 °C) - enables reliable CPU/motherboard junction temperature tracking for thermal throttling decisions. |
| Remote Diode Error | ±4 °C (max, −40 °C to +125 °C) - supports precise external die temperature sensing using standard 2N3904 or Pentium diodes. |
| Supply Voltage Range | 2.8 V to 3.8 V - compatible with 3.3 V system rails and tolerant of typical desktop/server supply variation. |
| ADC & DAC Resolution | 8 bits - delivers 1.0 °C temperature LSB and 256-step fan control granularity for deterministic closed-loop regulation. |
| Fan Count Full Scale | 255 counts - maps to stopped/slow fan condition; nominal 153 count corresponds to programmable 1100–8800 RPM range per channel. |
| SMBus Timing | t1 = 2.5 μs min clock period - ensures interoperability with standard SMBus 100 kHz and fast-mode 400 kHz controllers. |
Pinout & Package
LM87CIMT is housed in a 24-pin TSSOP (PW0024A) package with 0.65 mm pitch, optimized for high-density motherboard layouts and thermal performance (θJA = 95 °C/W).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| ADD/NTEST_OUT | Address select / NAND test output | Configures SMBus slave address LSBs (00, 01, or 10); enables board-level connectivity testing when driven externally. |
| THERM# | Open-drain thermal interrupt output | Asserts low on temperature limit violation only; dedicated signal path avoids masking by general INT# events. |
| SMBData | Bidirectional SMBus data line | Open-drain I/O with 100 kΩ internal pullup; supports multi-master arbitration and Alert Response Protocol. |
| FAN1/AIN1−, FAN2/AIN2 | Dual-function Schmitt-trigger inputs | Programmable as tachometer pulse counters (fan RPM) or 0–2.5 V analog voltage monitors with 12 μA input bias. |
| D1−, D1+, D2−, D2+ | Remote diode sensing terminals | Support two independent external temperature diodes (e.g., CPU core and GPU die) with dedicated bias and filtering paths. |
| DACOut/NTEST_IN | 8-bit DAC output / test input | 0–2.5 V analog output for fan speed control; forced high at power-up enters NAND Tree Test mode. |
| VID0–VID4 | Processor voltage ID inputs | Read Pentium/PRO/PII VID codes to determine core voltage; configurable as IRQ inputs if VID unused. |
| RESET# | Open-drain master reset output | Active-low 20 ms minimum pulse; can be enabled via Configuration Register Bit 4 for system-level cold reset initiation. |
Key Features
| Feature | Design Value |
|---|---|
| ΣΔ ADC architecture | Enables stable voltage and temperature measurements in electrically noisy PC environments without external filtering. |
| Programmable fan divisor | Four selectable divisors (1–4) allow precise RPM-to-count mapping across wide fan speed ranges (1100–8800 RPM). |
| Dual interrupt outputs (INT#, THERM#) | Separate masking and status registers let thermal events trigger immediate action without interfering with general fault reporting. |
| Chassis intrusion latch | CI pin latches high on case opening regardless of LM87 power state; internal open-drain output generates 20 ms pulse for logging. |
| Hardware watchdog registers | Non-volatile high-limit storage (13h/14h/17h/18h) with lock bits prevents accidental overwrite during runtime firmware updates. |
Applications
| Server Thermal Management | Workstation Power Monitoring |
|---|---|
|
Use Scenario: Real-time monitoring of CPU, GPU, and VRM temperatures alongside +12 V, +5 V, and Vccp1 rails in 1U/2U rack servers. IC Role / Device Role / Timing Role: Central hardware monitor acquiring temperature, voltage, and fan data every ~0.28 s; triggers THERM# on thermal violation to initiate throttling or shutdown. Use Value: Prevents thermal runaway by correlating remote diode readings with local junction temperature and fan response latency. |
Use Scenario: Continuous validation of multiple power domains (+3.3 V, +2.5 V, Vccp2) and chassis intrusion status in high-end CAD/CAM workstations. IC Role / Device Role / Timing Role: System supervisor IC reading VID0–VID4 to confirm processor voltage compliance and logging CI events to BIOS security log. Use Value: Ensures stable operation under sustained computational load by detecting undervoltage conditions before logic errors occur. |
| PC Motherboard Health Monitoring | Network Equipment Environmental Control |
|
Use Scenario: Fan speed regulation and +12 V/+5 V rail supervision on ATX motherboards with Intel Pentium II/III processors. IC Role / Device Role / Timing Role: Dual-role pin controller managing FAN1/FAN2 as tach inputs while using DACOut to drive 4-wire PWM fans via external transistor. Use Value: Reduces acoustic noise by dynamically adjusting fan speed based on internal/remote temperature deltas with 1 °C resolution. |
Use Scenario: Temperature and supply voltage telemetry in carrier-grade Ethernet switches with redundant 12 V power feeds. IC Role / Device Role / Timing Role: Hardware monitor interfacing with baseboard management controller (BMC) over SMBus to report ambient, ASIC, and PSU temperatures. Use Value: Enables predictive maintenance by trending remote diode drift and voltage droop across extended operating cycles. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar hardware monitoring applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LM92CIMM | Single-channel remote diode sensing; no VID inputs, no DAC, no chassis intrusion; 16-pin WSON package. | Limited to basic temperature-only monitoring in space-constrained embedded systems without fan control or voltage tracking. | Select when only high-accuracy local/remote temperature is needed and SMBus bandwidth or pin count must be minimized. |
| ADM1027ARQZ | 12-bit ADC/DAC; supports 3 remote diodes; includes SMBus Alert Response; 32-pin QSOP package. | Higher-resolution telemetry and expanded thermal channels for multi-socket servers requiring finer-grained thermal zoning. | Choose for enhanced precision and scalability where LM87CIMT's 8-bit resolution or 2-diode limit is insufficient. |
Compared with LM92CIMM, LM87CIMT adds full voltage monitoring, fan control, and VID support at the cost of larger footprint and higher complexity; versus ADM1027ARQZ, it trades resolution and channel count for lower cost and proven integration in legacy x86 platforms.
Availability
LM87CIMT is available at Aetrix Electronics and suitable for server thermal management, workstation power monitoring, and PC motherboard health supervision requiring stable component supply and long-term industrial lifecycle support.
Supply support for LM87CIMT 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 solutions.
The LM87CIMT belongs to TI's hardware monitor IC product line, designed specifically for real-time thermal, voltage, and fan telemetry in x86-based computing platforms - balancing integration, accuracy, and SMBus interoperability for mainstream PC and server applications.
FAQ
What is the primary function of the LM87CIMT in a computer system?
The LM87CIMT serves as a centralized hardware monitor IC that acquires and reports real-time data on system voltages (+12 V, +5 V, +3.3 V, etc.), internal and remote temperatures (via on-chip sensor and two external diodes), and fan speeds. It compares these values against programmable thresholds and asserts INT# or THERM# interrupts to alert the host system of faults - making LM87CIMT essential for thermal safety, power integrity, and system health diagnostics in PCs and servers.
Does the LM87CIMT support both SMBus and I²C protocols?
Yes, the LM87CIMT features a serial interface fully compatible with both SMBus 1.0/2.0 and standard I²C protocols. It operates as a slave device with a fixed 7-bit address format (01011XY) determined by the ADD pin state, supports clock stretching, Alert Response Protocol, and serial bus timeout recovery - ensuring seamless integration into existing motherboard management controllers regardless of underlying bus protocol implementation.
How does the LM87CIMT handle remote temperature sensing?
The LM87CIMT supports two independent remote diode temperature channels using dedicated D1+/D1− and D2+/D2− pins. It measures voltage drop across external transistors (e.g., 2N3904) or processor-integrated diodes, converting results to 8-bit digital words with ±4 °C max error over −40 °C to +125 °C. Each channel includes internal biasing and filtering to reject noise, and the LM87CIMT automatically compensates for series resistance in the diode connection path.
Can the LM87CIMT control fan speed directly?
The LM87CIMT includes an 8-bit DAC with 0–2.5 V output (DACOut pin) that can directly drive external fan control circuitry - such as a transistor-based PWM generator or linear fan driver. While it does not generate PWM signals natively, its DAC output provides precise analog voltage control, enabling closed-loop fan speed regulation based on temperature feedback. Fan tachometer inputs (FAN1/FAN2) provide real-time RPM verification for system-level control algorithms.
What is the significance of the VID0–VID4 inputs on the LM87CIMT?
The VID0–VID4 inputs on the LM87CIMT read voltage identification codes from Pentium/PRO and Pentium II processors to determine the required core supply voltage (Vccp). These 5-bit digital inputs are sampled and stored in the VID/Fan Divisor Register (47h) and VID4 Register (49h), allowing system firmware to validate correct VRM configuration and detect mismatches. When VID monitoring is disabled, these pins function as general-purpose IRQ inputs - adding flexibility in resource-constrained designs.
LM87CIMT Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- -
- Package/Case:
- 24-TSSOP (0.173", 4.40mm Width)
- Packaging:
- Tube
- Product Status:
- Not For New Designs
- Function:
- Hardware Monitor
- Sensor Type:
- Internal and External
- Sensing Temperature:
- -40°C ~ 125°C
- Accuracy:
- ±3°C Local(Typ), ±4°C Remote(Max)
- Topology:
- ADC (Sigma Delta), Comparator, Fan Speed Counter, Register Bank
- Output Type:
- 2-Wire Serial, I2C/SMBUS
- Output Alarm:
- No
- 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
LM87CIMT FAQ
1.How can I place an order for LM87CIMT through Aetrix?
Please submit a Request for Quotation (RFQ) for LM87CIMT 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 LM87CIMT reliable?
The price and inventory of LM87CIMT are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LM87CIMT is usually 5 days.
3.What payment methods are accepted for LM87CIMT?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LM87CIMT transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LM87CIMT?
LM87CIMT orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LM87CIMT 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 LM87CIMT?
For technical support, including LM87CIMT datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LM87CIMT requirements.
6.How does Aetrix verify that LM87CIMT is sourced from the original manufacturer or authorized distributors?
All LM87CIMT 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 LM87CIMT meets industry standards.
7.What is the process for return or replacement of LM87CIMT?
All LM87CIMT units undergo pre-shipment inspection (PSI). If there is an issue with LM87CIMT, 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 LM87CIMT part is unused and in its original packaging.
Return procedure for LM87CIMT:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
LM87CIMT 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
Microchip Technology
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SE98ATP,547
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AMC6821SDBQR
Texas Instruments
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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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