LM81
Serial Interface ACPI-Compatible Microprocessor System
Hardware Monitor
General Description
The LM81 is a highly integrated data acquisition system for
hardware monitoring of servers, Personal Computers, or vir-
tually any microprocessor-based system. In a PC, the LM81
can be used to monitor power supply voltages, tempera-
tures, and fan speeds. Actual values for these inputs can be
read at any time. Programmable WATCHDOG
TM
limits in the
LM81 activate a fully programmable and maskable interrupt
system with two outputs (INT and T_CRIT_).
The LM81 has an on-chip digital output temperature sensor
with 9-bit or 12-bit resolution, a 6 analog input ADC with 8-bit
resolution and an 8-bit DAC. Two fan tachometer outputs
can be measured with the LM81's FAN1 and FAN2 inputs.
The DAC, with a 0 to 1.25V output voltage range, can be
used for fan speed control. Additional inputs are provided for
Chassis Intrusion detection circuits, and VID monitor inputs.
The LM81 has a Serial Bus interface that is compatible with
SMBus
TM
.
Features
n
Temperature sensing
n
6 positive voltage inputs with scaling resistors for
monitoring +5V, +12V, +3.3V, +2.5V, Vccp power
supplies directly
n
8-bit DAC output for controlling fan speed
n
2 fan speed monitoring inputs
n
Chassis Intrusion Detector input
n
WATCHDOG
TM
comparison of all monitored values
n
SMBus Serial Bus interface compatibility
n
VID0-VID4 monitoring inputs
Key Specifications
n
Voltage monitoring
Error
+2% (max)
n
Temperature Error
-40C to +125C
3C (max)
n
Supply Voltage Range
2.8V to 3.8V
n
Supply Current
Operating:
0.4 mA (typ)
n
ADC and DAC Resolution
8 Bits
n
Temperature Resolution
0.5C
Applications
n
System Thermal and Hardware Monitoring for Servers
and PCs
n
Office Electronics
n
Electronic Test Equipment and Instrumentation
Typical Application
TRI-STATE
is a registered trademark of National Semiconductor Corporation.
WATCHDOG
TM
is a trademark of National Semiconductor Corporation.
SMBus
TM
is a trademark of the Intel Corporation.
DS100072-1
# Indicates Active Low ("Not")
June 1999
LM81
Serial
Interface
ACPI-Compatible
Microprocessor
System
Hardware
Monitor
1999 National Semiconductor Corporation
DS100072
www.national.com
Ordering Information
Temperature Range
NS Package
Number
-40C
T
A
+125C
Order Number
Device Marking
LM81CIMT-3
1
LM81CIMT-3
MTC24B
LM81CIMTX-3
2
LM81CIMT-3
MTC24B
Note:
1
-Rail transport media, 62 parts per rail
2
-Tape and reel transport media, 3400 parts per reel
Connection Diagram
Block Diagram
Pin Description
Pin
Name(s)
Pin
Number
Number
of Pins
Type
Description
A0/NTEST_OUT
1
1
Digital I/0
The lowest order programmable bit of the serial bus address. This
pin functions as an output during NAND Tree tests (board-level
connectivity testing). Refer to
SECTION 11 on NAND Tree testing.
A1
2
1
Digital Input
The highest order programmable bit of the serial bus address.
SMBData
3
1
Digital I/O
Serial Bus bidirectional Data. Open-drain output.
DS100072-3
DS100072-2
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2
Pin Description
(Continued)
Pin
Name(s)
Pin
Number
Number
of Pins
Type
Description
SMBCLK
4
1
Digital Input
Serial Bus Clock.
FAN1-FAN2
5-6
2
Digital Inputs
Schmitt Trigger fan tachometer inputs.
CI
7
1
Digital I/O
An active high input from an external circuit which latches a
Chassis Intrusion event. This line can go high without any
clamping action regardless of the powered state of the LM81.
There is also an internal open-drain output on this line, controlled
by Bit 6 of the Configuration Register (40h) or Bit 7 CI Clear
Register (46h), to provide a minimum 20 ms reset pulse. See
Section 3.3 and Section 9.0.
T_CRIT_A
8
1
Digital Output
Critical Temperature Alarm active low open-drain output. This pin
can be grounded when not used.
V
+
(+2.8V to
+3.8V)
9
1
POWER
+3.3V V
+
power. Bypass with the parallel combination of 10 F
(electrolytic or tantalum) and 0.1 F (ceramic) bypass capacitors.
INT
10
1
Digital Output
Interrupt active low open-drain output. This output is enabled when
Bit 1 in the Configuration Register is set to 1. The default state is
disabled.
DACOut/NTEST_IN
11
1
Analog
Output/Digital
Input
0V to +1.25V amplitude 8-bit DAC output. When forced high by an
external voltage the NAND Tree Test mode is enabled which
provides board-level connectivity testing. Refer to Section 11.0 on
NAND Tree testing.
RESET
12
1
Digital I/O
Master Reset, 5 mA driver (open-drain), active low output with a
20 ms minimum pulse width. Available when enabled via Bit 4 in
the Configuration register. It acts as an active low power on
RESET input.
GND
13
1
GROUND
Internally connected to all circuitry. The ground reference for all
analog inputs and the DAC output. This pin needs to be
connected to a low noise analog ground plane for optimum
performance of the DAC output.
Vccp2
14
1
Analog Input
Analog input for monitoring -12V or Vccp2. Selectable by
choosing the appropriate external resistor divider values such that
the input to the LM81 is scaled to +2.5V. See
Section 4.0.
+12Vin
15
1
Analog Input
Analog input for monitoring +12V.
+5Vin
16
1
Analog Input
Analog input for monitoring +5V.
+3.3Vin
17
1
Analog Input
Analog input for monitoring +3.3V.
+2.5Vin
18
1
Analog Input
Analog input for monitoring +2.5V.
Vccp1
19
1
Analog Input
Analog input for monitoring Vccp, a processor voltage that is
nominally at +2.5V.
VID4-VID0
20-24
5
Digital Inputs
Supply Voltage readouts from the Pentium/PRO power supplies
that indicate the operating voltage or the processor (e.g. 1.5V to
2.9V). The values are read in the VID/Fan Divisor Register and
the VID4 Register.
TOTAL PINS
24
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3
Absolute Maximum Ratings
(Notes 1, 2)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Positive Supply Voltage (V
+
)
+6.0V
Voltage on Any Input or Output Pin:
+12Vin, T_CRIT_A
-0.3V to +15V
A0, A1, DACOut
-0.3V to (V
+
+ 0.3V)
+2.5Vin, +3.3Vin
(Note 3)
All other pins
-0.3V to +6V
Input Current at any Pin (Note 4)
5 mA
Package Input Current (Note 4)
20 mA
Maximum Junction Temperature
(T
J
max)
150C
ESD Susceptibility (Note 6)
Human Body Model
2000V
Machine Model
200V
Soldering Information
MTC Package (Note 7) :
Vapor Phase (60 seconds)
215C
Infrared (15 seconds)
235C
Storage Temperature
-65C to +150C
Operating Ratings
(Notes 1, 2)
Operating Temperature Range
T
MIN
T
A
T
MAX
LM81
-55C
T
A
+125C
Specified Temperature Range
T
MIN
T
A
T
MAX
LM81
-40C
T
A
+125C
Junction to Ambient Thermal Resistance (
JA
(Note 5))
NS Package Number: MTC24B
95C/W
Supply Voltage (V
+
)
+2.8V to +3.8V
V
IN
Voltage Range:
+12Vin
-0.05V to +15V
+5Vin
-0.05V to +6.8V
+3.3Vin
-0.05V to +4.6V
+2.5Vin
-0.05V to +3.6V
VID0 - VID4, Vccp
-0.05V to +6.0V
All other inputs
-0.05V to (V
+
+ 0.05V)
DC Electrical Characteristics
The following specifications apply for +2.8V
DC
V
+
+3.8V
DC
, R
S
= 500
, unless otherwise specified. Boldface limits apply
for T
A
= T
J
= T
MIN
to T
MAX
; all other limits T
A
= T
J
= 25C. (Note 8)
Symbol
Parameter
Conditions
Typical
Limits
Units
(Note 9)
(Note 10)
(Limits)
POWER SUPPLY CHARACTERISTICS
I
+
Supply Current
Interface Inactive
400
900
A (max)
TEMPERATURE-TO-DIGITAL CONVERTER CHARACTERISTICS
Error
-40C
T
A
+125C
3
C (max)
Resolution
9-bit mode
12-bit mode
0.5
0.0625
C (min)
C (min)
LM81 ANALOG-TO-DIGITAL CONVERTER CHARACTERISTICS
Resolution
8
bits
TUE
Total Unadjusted Error
+2.5Vin,
+3.3Vin, +5Vin
(Notes 11, 12)
+2
+0.8
% (max)
% (min)
Vccp1, Vccp2
(Note 11)
+2.4
0
% (max)
% (min)
+12Vin
(Notes 11, 12)
+3.1
+1.2
% (max)
% (min)
DNL
Differential Non-Linearity
1
LSB (max)
PSS
Power Supply Sensitivity
0.4
%/V
t
C
Total Monitoring Cycle Time
(Note 13)
9-bit Temp Resolution
12-bit Temp Resolution
0.4
0.82
1.2
sec
sec (max)
sec (max)
ADC INPUT CHARACTERISTICS
Input Resistance (All analog inputs except
Vccp1 and Vccp2)
115
90
k
(min)
Vccp1 and Vccp2 DC Input Current
1
A
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DC Electrical Characteristics
(Continued)
The following specifications apply for +2.8V
DC
V
+
+3.8V
DC
, R
S
= 500
, unless otherwise specified. Boldface limits apply
for T
A
= T
J
= T
MIN
to T
MAX
; all other limits T
A
= T
J
= 25C. (Note 8)
Symbol
Parameter
Conditions
Typical
Limits
Units
(Note 9)
(Note 10)
(Limits)
DAC CHARACTERISTICS
Resolution
8
Bits
DAC Error
V
+
= 3.3V
5
62.5
% (max)
mV (max)
DAC Error Temperature Sensitivity
100
ppm/C (max)
DAC Error Power Supply Sensitivity
1.5
%/V (max)
R
L
Output Load Resistance
V
O
= 1.25V
625
(min)
C
L
Output Load Capacitance
20
pF (max)
FAN RPM-TO-DIGITAL CONVERTER
Fan RPM Error
+25C
T
A
+75C
10
% (max)
-10C
T
A
+100C
15
% (max)
-40C
T
A
+125C
20
% (max)
Full-scale Count
255
(max)
FAN1 and FAN2 Nominal Input
RPM (See
Section 6.0)
Divisor = 1, Fan Count =
153 (Note 14)
8800
RPM
Divisor = 2, Fan Count =
153 (Note 14)
4400
RPM
Divisor = 3, Fan Count =
153 (Note 14)
2200
RPM
Divisor = 4, Fan Count =
153 (Note 14)
1100
RPM
Internal Clock Frequency
+25C
T
A
+75C
22.5
20.2
kHz (min)
24.8
kHz (max)
-10C
T
A
+100C
22.5
19.1
kHz (min)
25.9
kHz (max)
-40C
T
A
+125C
22.5
18
27
kHz (min)
kHz (max)
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