LM78
Microprocessor System Hardware Monitor
General Description
The LM78 is a highly integrated Data Acquisition system for
hardware monitoring of servers, Personal Computers, or
virtually any microprocessor based system. In a PC, the
LM78 can be used to monitor power supply voltages, tem-
peratures, and fan speeds. Actual values for these inputs
can be read at any time, and programmable WATCHDOG
limits in the LM78 activate a fully programmable and
maskable interrupt system with two outputs.
The LM78 has an on-chip temperature sensor, 5 positive
analog inputs, two inverting inputs (for monitoring negative
voltages), and an 8-bit ADC. An input is provided for the
overtemperature outputs of additional temperature sensors
and this is linked to the interrupt system. The LM78 provides
inputs for three fan tachometer outputs. Additional inputs are
provided for Chassis Intrusion detection circuits, VID monitor
inputs, and chainable interrupt. The LM78 provides both ISA
and Serial Bus interfaces. A 32-byte auto-increment RAM is
provided for POST (Power On Self Test) code storage.
Applications
n
System Hardware Monitoring for Servers and PCs
n
Office Electronics
n
Electronic Test Equipment and Instrumentation
Features
n
Temperature sensing
n
5 positive voltage inputs
n
2 op amps for negative voltage monitoring
n
3 fan speed monitoring inputs
n
Input for additional temperature sensors
n
Chassis Intrusion Detector input
n
WATCHDOG comparison of all monitored values
n
POST code storage RAM
n
ISA and I
2
C
TM
Serial Bus interfaces
Key Specifications
j
Voltage monitoring
accuracy
1% (max)
j
Temperature Accuracy
-10C to +100C
3C (max)
j
Supply Voltage
5V
j
Supply Current
Operating:
1 mA typ
Shutdown:
10 A typ
j
ADC Resolution
8 Bits
Typical Application
I2C
is a registered trademark of the Phillips Corporation.
DS012873-1
# indicates Active Low ("Not")
February 2000
LM78
Microprocessor
System
Hardware
Monitor
2001 National Semiconductor Corporation
DS012873
www.national.com
Ordering Information
Temperature Range
Package
-10C
T
A
+100C
Order Number
Device Marking
LM78CCVF
LM78CCVF-J
VGZ44A
Connection Diagram
Block Diagram
DS012873-2
DS012873-3
LM78
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2
Pin Descriptions
Pin
Name(s)
Pin
Number
Number
of Pins
Type
Description
IORD
1
1
Digital Input
An active low standard ISA bus I/O Read Control.
IOWR
2
1
Digital Input
An active low standard ISA bus I/O Write Control.
SYSCLK
3
1
Digital Input
The reference clock for the ISA bus. Typically ranges from 4.167 MHz to
8.33 MHz. The minimum clock frequency this input can handle is 1 Hz.
D7D0
411
8
Digital I/O
Bi-directional ISA bus Data lines. D0 corresponds to the low order bit,
with D7 the high order bit.
V
CC
(+5V)
12
1
POWER
+5V V
CC
power. Bypass with the parallel combination of 10 F
(electolytic or tantalum) and 0.1 F (ceramic) bypass capacitors.
GNDD
13
1
GROUND
Internally connected to all digital circuitry.
SMI__IN
14
1
Digital Input
Chainable SMI (System Management Interrupt) Input. This is an active
low input that propagates the SMI signal to the SMI output of the LM78
via SMI Mask Register Bit 6 and SMI enable Bit 1 of the Configuration
Register.
Chassis
Intrusion
15
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 LM78. The LM78 provides an
internal open drain on this line, controlled by Bit 7 of NMI Mask Register
2, to provide a minimum 20 ms reset of this line.
Power
Switch
Bypass
16
1
Digital Output
An active low push-pull output intended to drive an external P-channel
power MOSFET for software power control.
FAN3FAN1
1719
3
Digital Input
0V to +5V amplitude fan tachometer input.
SCL
20
1
Digital Input
Serial Bus Clock.
SDA
21
1
Digital I/O
Serial Bus bidirectional Data.
RESET
22
1
Digital Output
Master Reset, 5 mA driver (open drain), active low output with a 20 ms
minimum pulse width. Available when enabeld via Bit 7 in SMI Mask
Register 2.
NTEST
23
1
Test Output
NAND Tree totem-pole output that provides board-level connectivity
testing. Refer to Section 11.0 on NAND Tree testing.
GNDA
24
1
GROUND
Internally connected to all analog circuitry. The ground reference for all
analog inputs.
-IN6
25
1
Analog Input
Ground-referred inverting op amp input. Refer to Section 4.0, "ANALOG
INPUTS".
FB6
26
1
Analog Output
Output of inverting op amp for Input 6. Refer to section 4.0, "ANALOG
INPUTS".
FB5
27
1
Analog Output
Output of inverting op amp for Input 5. Refer to section 4.0, "ANALOG
INPUTS".
-IN5
28
1
Analog Input
Ground-referred inverting op amp input. Refer to Section 4.0, "ANALOG
INPUTS".
IN4IN0
2933
5
Analog Input
0V to 4.096V FSR Analog Inputs.
VID3VID0
3437
4
Digital Input
Voltage Supply readouts from P6. This value is read in the VID/Fan
Divisor Register.
BTI
38
1
Digital Input
Board Temperature Interrupt driven by O.S. outputs of additional
temperature sensors such as LM75. Provides internal pull-up of 10 k
.
NMI/IRQ
39
1
Digital Output
Non-Maskable Interrupt (open source)/Interrupt Request (open drain).
The mode is selected with Bit 5 of the Configuration Register and the
output is enabled when Bit 2 of the Configuration Register is set to 1.
The default state is disabled and IRQ mode.
SMI
40
1
Digital Output
System Management Interrupt (open drain). This output is enabled when
Bit 1 in the Configuration Register is set to 1. The default state is
disabled.
LM78
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Pin Descriptions
(Continued)
Pin
Name(s)
Pin
Number
Number
of Pins
Type
Description
A2A0
4143
3
Digital Input
The three lowest order bits of the 16-bit ISA Address Bus. A0
corresponds to the lowest order bit.
CS
44
1
Digital Input
Chip Select input from an external decoder which decodes high order
address bits on the ISA Address Bus. This is an active low input.
TOTAL PINS
44
LM78
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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
CC
)
6.5V
Voltage on Any Input or Output Pin
-0.3V to (V
CC
+0.3V)
Ground Difference (GNDDGNDA)
300 mV
Input Current at any Pin (Note 3)
5 mA
Package Input Current (Note 3)
20 mA
Maximum Junction Temperature
(T
J
max)
150C
ESD Susceptibility(Note 5)
Human Body Model
2000V
Machine Model
175V
Soldering Information
PQFP Package (Note 6) :
Vapor Phase (60 seconds)
215C
Infrared (15 seconds)
220C
Storage Temperature
-65C to +150C
Operating Ratings
(Notes 1, 2)
Operating Temperature Range
T
MIN
T
A
T
MAX
LM78
-55C
T
A
+125C
Specified Temperature Range
T
MIN
T
A
T
MAX
LM78
-10C
T
A
+100C
Junction to Ambient Thermal Resistance (
JA
(Note 4) )
NS Package ID: VGZ44A
62C/W
Supply Voltage (V
CC
)
+4.25V to +5.75V
Ground Difference
(IGNDDGNDAI)
100 mV
V
IN
Voltage Range
-0.05V to V
CC
+ 0.05V
DC Electrical Characteristics
(Note 7)
The following specifications apply for +4.25 V
DC
V
CC
+5.75 V
DC
, f
SYSCLK
= 8.33 MHz, R
S
= 25
, unless otherwise speci-
fied. Boldface limits apply for T
A
= T
J
= T
MIN
to T
MAX
; all other limits T
A
= T
J
= 25C.
Symbol
Parameter
Conditions
Typical
Limits
Units
(Note 8)
(Note 9)
(Limits)
POWER SUPPLY CHARACTERISTICS
I
CC
Supply Current
Interface Inactive
1.0
2
mA (max)
Shutdown Mode
10
A
TEMPERATURE-TO-DIGITAL CONVERTER CHARACTERISTICS
Accuracy
-10C
T
A
+100C
3
C (max)
Resolution
1
C (min)
ANALOG-TO-DIGITAL CONVERTER CHARACTERISTICS
Resolution (8 bits with full-scale at 4.096V)
16
mV
TUE
Total Unadjusted Error
(Note 10)
1
% (max)
DNL
Differential Non-Linearity
1
LSB
PSS
Power Supply Sensitivity
1
%/V
t
C
Total Monitoring Cycle Time
(Note 11)
1.0
1.5
sec (max)
OP AMP CHARACTERISTICS
Output Current (Sourcing)
50
A
Input Offset Voltage
I
OUT
= 50 A
1
mV
Input Bias Current
0.1
nA
PSRR
60
dB
DC Open Loop Gain
70
dB
Gain Bandwidth Product
500
kHz
MULTIPLEXER/ADC INPUT CHARACTERISTICS
On Resistance
400
2000
(max)
Off Channel Leakage Current
0.1
nA
Input Current (On Channel Leakage Current)
0.1
nA
FAN RPM-TO-DIGITAL CONVERTER
Accuracy
+25C
T
A
+75C
10
% (max)
-10C
T
A
+100C
15
% (max)
Full-scale Count
255
(max)
LM78
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