November 2004

1

MIC281

MIC281

Micrel

MIC281

Low-Cost IttyBitty™ Thermal Sensor IttyBitty®

REV 11/04

General Description

The MIC281 is a digital thermal sensor capable of measuring

the temperature of a remote PN junction. It is optimized for

applications favoring low cost and small size. The remote

junction may be an inexpensive commodity transistor, e.g.,

2N3906, or an embedded thermal diode such as found in

Intel Pentium* II/III/IV CPUs, AMD Athlon* CPUs, and Xilinx

Virtex* FPGAs.

The MIC281 is 100% software and hardware backward com-

patiblewiththeMIC280andfeaturesthesameindustry-leading

noise performance and small size. The advanced integrating

A/Dconverterandanalogfront-endreduceerrorsduetonoise

for maximum accuracy and minimum guardbanding.

A2-wire SMBus 2.0-compatible serial interface is provided for

host communication. The clock and data pins are 5V-tolerant

lines low even if the device is powered down.

Superior performance, low power, and small size make the

MIC281 an excellent choice for cost-sensitive thermal man-

agement applications.

Typical Application

DATA

5

4

2

3

1

TO

SERIAL BUS

HOST

CPU DIODE

2000pF

MIC281

CLK

NC

3.3V

10k

pull-ups

VDD

T1

GND

0.1µF

MIC281 Typical Application

Features

• Remote temperature measurement using embedded

thermal diodes or commodity transistors

• Accurate remote sensing

±3°C max., 0°C to 100°C

• Excellent noise rejection

• SMBus timeout to prevent bus lockup

• Voltage tolerant I/Os

• Low power shutdown mode

• Failsafe response to diode faults

• 3.0V to 3.6V power supply range

• IttyBitty™ SOT23-6 Package

Applications

• Desktop, server and notebook computers

• Set-top boxes

• Game consoles

• Appliances

Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com

IttyBitty is a registered trademark of Micrel, Inc.

*All trademarks are the property of their respective owners.