LM81CIMT-3 Equivalent & Substitute Parts

Part Overview

The LM81CIMT-3 is a hardware monitor integrated circuit manufactured by Texas Instruments, designed for system monitoring applications. It provides internal and external temperature sensing with 2-Wire SMBus communication interface, integrated fan speed control, and alarm output capabilities. The device operates across a -40°C to 125°C temperature range with ±3°C accuracy.

The LM81CIMT-3 is classified as obsolete. Identifying equivalent and substitute parts is necessary to maintain design continuity, ensure supply chain availability, and support long-term product maintenance and production requirements.

Key Parameters

Parameter	Specification
Function	Hardware Monitor
Sensor Type	Internal and External
Sensing Temperature Range	-40°C ~ 125°C
Temperature Accuracy	±3°C (Max)
Output Type	2-Wire SMBus
Output Alarm	Yes
Output Fan Control	Yes
Supply Voltage	2.8V ~ 3.8V
Operating Temperature	-40°C ~ 125°C
Package / Case	24-TSSOP (0.173", 4.40mm Width)
Mounting Type	Surface Mount
Topology	ADC (Sigma Delta), Comparator, Fan Speed Control, Register Bank

Substitute Part Grouping Explanation

Substitute parts for the LM81CIMT-3 are qualified based on the following critical parameters that determine functional and mechanical compatibility:

Function: Hardware Monitor
Sensor Type: Internal and External
Sensing Temperature Range: -40°C ~ 125°C
Temperature Accuracy: ±3°C (Max)
Output Type: 2-Wire SMBus
Output Alarm: Yes
Output Fan Control: Yes
Supply Voltage: 2.8V ~ 3.8V
Operating Temperature: -40°C ~ 125°C
Package / Case: 24-TSSOP (0.173", 4.40mm Width)
Mounting Type: Surface Mount

All identified substitute parts maintain identical electrical specifications and mechanical packaging, ensuring direct functional equivalence in system applications.

Parameter Comparison

Parameter	LM81CIMT-3	LM81CIMT-3/NOPB	LM81BIMT-3/NOPB
Manufacturer	Texas Instruments	Texas Instruments	National Semiconductor
Function	Hardware Monitor	Hardware Monitor	Hardware Monitor
Sensor Type	Internal and External	Internal and External	Internal and External
Sensing Temperature Range	-40°C ~ 125°C	-40°C ~ 125°C	-40°C ~ 125°C
Temperature Accuracy	±3°C (Max)	±3°C (Max)	±3°C (Max)
Output Type	2-Wire SMBus	2-Wire SMBus	2-Wire SMBus
Output Alarm	Yes	Yes	Yes
Output Fan Control	Yes	Yes	Yes
Supply Voltage	2.8V ~ 3.8V	2.8V ~ 3.8V	2.8V ~ 3.8V
Operating Temperature	-40°C ~ 125°C	-40°C ~ 125°C	-40°C ~ 125°C
Package / Case	24-TSSOP	24-TSSOP	24-TSSOP
Mounting Type	Surface Mount	Surface Mount	Surface Mount
Topology	ADC (Sigma Delta), Comparator, Fan Speed Control, Register Bank	ADC (Sigma Delta), Comparator, Fan Speed Control, Register Bank	ADC (Sigma Delta), Comparator, Fan Speed Control, Register Bank
Product Status	Obsolete	Obsolete	Active
RoHS Status	RoHS non-compliant	ROHS3 Compliant	Not specified

Engineering Selection Recommendations

LM81CIMT-3/NOPB is a direct substitute with identical electrical and mechanical specifications. This variant carries ROHS3 compliance, making it suitable for applications requiring RoHS certification. The /NOPB designation indicates lead-free plating, providing environmental compliance advantages over the original LM81CIMT-3.

LM81BIMT-3/NOPB is a parametric equivalent manufactured by National Semiconductor. All electrical specifications, temperature ranges, accuracy, and package dimensions are identical to the main part. This device maintains active product status, providing superior long-term availability compared to the obsolete LM81CIMT-3. The LM81BIMT-3/NOPB is suitable for new designs and production continuity where supply of the original part is constrained.

Selection between LM81CIMT-3/NOPB and LM81BIMT-3/NOPB should be based on supply availability, compliance requirements, and manufacturer preference. Both parts are electrically and mechanically interchangeable.

Frequently Asked Questions (FAQ)

Q: Can LM81CIMT-3/NOPB be used as a direct replacement for LM81CIMT-3?

A: Yes. LM81CIMT-3/NOPB is a direct substitute with identical electrical specifications, temperature range, accuracy, output types, and 24-TSSOP packaging. The primary difference is RoHS3 compliance and lead-free plating in the /NOPB variant.

Q: What is the difference between LM81CIMT-3/NOPB and LM81BIMT-3/NOPB?

A: Both parts are parametric equivalents with identical electrical and mechanical specifications. The primary differences are manufacturer (Texas Instruments vs. National Semiconductor) and product status (Obsolete vs. Active). LM81BIMT-3/NOPB offers superior long-term availability due to active production status.

Q: Are all substitute parts compatible with the same PCB layout?

A: Yes. All substitute parts use the 24-TSSOP package with identical pin configuration and mechanical dimensions (0.173", 4.40mm Width). No PCB layout modifications are required.

Q: Which substitute part should be selected for new designs?

A: LM81BIMT-3/NOPB is recommended for new designs due to active product status and assured long-term supply availability. This part maintains all functional and electrical equivalence to the original LM81CIMT-3.

Q: Are there compliance differences between the substitute parts?

A: LM81CIMT-3/NOPB carries ROHS3 compliance. LM81BIMT-3/NOPB compliance status is not specified in available documentation. Verify compliance requirements with your design specifications and regulatory obligations.

Q: Can these parts be used interchangeably in existing production?

A: Yes. All substitute parts maintain identical electrical specifications, temperature ranges, accuracy, and package dimensions. No firmware, software, or circuit modifications are required for substitution.

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