LM87 Serial Interface System Hardware Monitor with Remote Diode Temperature Sensing
December 2003
LM87
Serial Interface System Hardware Monitor with Remote
Diode Temperature Sensing
General Description
The LM87 is a highly integrated data acquisition system for
hardware monitoring of servers, Personal Computers, or
virtually any microprocessor-based system. In a PC, the
LM87 can be used to monitor power supply voltages, moth-
erboard and processor temperatures, and fan speeds. Ac-
tual values for these inputs can be read at any time. Pro-
grammable WATCHDOG limits in the LM87 activate a fully
programmable and maskable interrupt system with two out-
puts (INT# and THERM#).
The LM87 has an on-chip digital output temperature sensor
with 8-bit resolution as well as the capability of monitoring 2
external diode temperatures to 8-bit resolution, an 8 channel
analog input ADC with 8-bit resolution and an 8-bit DAC. A
channel on the ADC measures the supply voltage applied to
the LM87, nominally 3.3 V. Two of the ADC inputs can be
redirected to a counter that can measure the speed of up to
2 fans. A slow speed
Σ∆
ADC architecture allows stable
measurement of signals in an extremely noisy environment.
The DAC, with a 0 to 2.5 V output voltage range, can be
used for fan speed control. Additional inputs are provided for
Chassis Intrusion detection circuits, and VID monitor inputs.
The VID monitor inputs can also be used as IRQ inputs if VID
monitoring is not required. The LM87 has a Serial Bus
interface that is compatible with SMBus
™
and I
2
C
™
.
n
n
n
n
n
n
n
2 inputs selectable for fan speed or voltage monitoring
8-bit DAC output for controlling fan speed
Chassis Intrusion Detector input
WATCHDOG comparison of all monitored values
SMBus or I
2
C Serial Bus interface compatibility
VID0-VID4 or IRQ0-IRQ4 monitoring inputs
On chip temperature sensor
Key Specifications
j
Voltage Monitoring Error
j
External Temperature Error
j
Internal Temperature Error
±
2 % (max)
±
4 ˚C (max)
±
3 ˚C (typ)
2.8 to 3.8 V
0.7 mA (typ)
8 Bits
1.0 ˚C
−40 ˚C to +125 ˚C
j
Supply Voltage Range
j
Supply Current
j
ADC and DAC Resolution
j
Temperature Resolution
Applications
n
System Thermal and Hardware Monitoring for Servers,
Workstations and PCs
n
Networking and Telecom Equipment
n
Office Electronics
n
Electronic Test Equipment and Instrumentation
Features
n
Remote diode temperature sensing (2 channels)
n
8 positive voltage inputs with scaling resistors for
monitoring +5 V, +12 V, +3.3 V, +2.5 V, Vccp power
supplies directly
Ordering Information
Temperature Range
−40 ˚C
≤
T
A
≤
+125 ˚C
Order Number
LM87CIMT
1
2
Connection Diagram
NS Package
Number
MTC24B
MTC24B
Device Marking
LM87CIMT
LM87CIMT
LM87CIMTX
2
Note:
1
-Rail transport media, 61 parts per rail
-Tape and reel transport media, 2500 parts per reel
10099503
SMBus
™
is a trademark of the Intel Corporation.
© 2003 National Semiconductor Corporation
DS100995
www.national.com
NSC [ NATIONAL SEMICONDUCTOR ]
