LMC6953
PCI Local Bus Power Supervisor
General Description
The LMC6953 is a voltage supervisory chip designed to
meet PCI (Peripheral Component Interconnect) Specifica-
tions Revision 2.1. It monitors 5V and 3.3V power supplies.
In cases of power-up, power-down, brown-out, power failure
and manual reset interrupt, the LMC6953 provides an active
low reset. RESET holds low for 100 ms after both 5V and
3.3V powers recover, or after manual reset signal returns to
high state. The external capacitor on pin 8 adjusts the reset
delay.
This part is ideal on PCI motherboards or add-in cards to en-
sure the integrity of the entire system when there is a fault
condition. The active low reset sets the microprocessor or lo-
cal device in a known state.
The LMC6953 has a built-in bandgap reference that accu-
rately determines all the threshold voltages. The internal re-
set delay circuitry eliminates additional discrete components.
Features
n
Compliant to PCI specifications revision 2.1.
n
Under and over voltage detectors for 5V and 3.3V
n
Power failure detection (5V falling under 3.3V by
300 mV max)
n
Manual reset input pin
n
Guaranteed RESET assertion at V
DD
= 1.5V
n
Integrated reset delay circuitry
n
Open drain output
n
Adjustable reset delay
n
Response time for over and under voltage detection:
490 ns Max
n
Power failure response time:
90 ns Max
n
Requires minimal external components
Applications
n
Desktop PCs
n
PCI-Based Systems
n
Network servers
Typical Application Circuits
On Mother Board
DS012846-23
On Add-in Cards
DS012846-24
April 1998
LMC6953
PCI
Local
Bus
Power
Supervisor
1998 National Semiconductor Corporation
DS012846
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Connection Diagram
Ordering Information
Package
Industrial Temp Range
NSC
Supplied
-40C to +85C
Drawing
As
8-Pin
Small
LMC6953CM
M08A
Rails
Outline
LMC6953CMX
2.5k Tape
and Reel
8Pin SO
DS012846-2
Top View
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2
Absolute Maximum Ratings
(Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
ESD Tolerance (Note 2)
Human Body Model
2 kV
Machine Model
200V
Voltage at Input Pin
7V
Supply Voltage
7V
Current at Output Pin
15 mA
Current at Power Supply Pin (Note 3)
10 mA
Lead Temp. (Soldering, 10 sec.)
260C
Storage Temperature Range
-65C to +150C
Junction Temperature
150C
Operating Ratings
(Note 1)
Supply Voltage
1.5V to 6V
Junction Temperature Range
LMC6953C
-40C to +85C
Thermal Resistance (
JA
)
M Package
165C/W
DC Electrical Characteristics
Unless otherwise specified, all boldface limits guaranteed for T
J
= -40C to +85C, V
DD
= 5V, R
PULL-UP
= 4.7 k
and C
EXT
=
0.01 F. Typical numbers are room temperature (25C) performance.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
V
H5
V
DD
Over-Voltage Threshold
T
J
= 0C to 70C
(Note 4)
5.45
5.60
5.75
V
T
J
= -40C to 85C
(Note 4)
5.30
5.60
5.90
V
V
L5
V
DD
Under-Voltage Threshold
T
J
= 0C to 70C
(Note 4)
4.25
4.40
4.55
V
T
J
= -40C to 85C
(Note 4)
4.10
4.40
4.70
V
V
H3.3
3.3V Over-Voltage Threshold
T
J
= 0C to 70C
(Note 5)
3.80
3.95
4.10
V
T
J
= -40C to 85C
(Note 5)
3.60
3.95
4.30
V
V
L3.3
3.3V Under-Voltage Threshold
T
J
= 0C to 70C
(Note 5)
2.50
2.65
2.80
V
T
J
= -40C to 85C
(Note 5)
2.30
2.65
3.00
V
V
MR
Manual RESET Threshold
2.50
2.80
V
V
PF
Power Failure Differential Voltage
(Note 6)
150
300
mV
(3.3V Pin5V Pin)
R
IN
Input Resistance at 5V and 3.3V Pins
35
k
V
OL
RESET Output Low
T
J
= 0C to 70C
V
DD
= 1.5V to 6V
0.05
0.10
V
T
J
= -40C to 85C
V
DD
= 1.55V to 6V
I
S
Supply Current
(Note 3)
0.8
1.50
mA
AC Electrical Characteristics
Unless otherwise specified, all boldface limits guaranteed for T
J
= -40C to 85C, V
DD
= 5V, R
PULL-UP
= 4.7 k
and C
EXT
= 0.01 F. Typical numbers are room temperature (25C) performance.
Symbol
Parameter
Conditions
Typ
LMC6953
Units
Limit
t
D
Over or Under Voltage Response Time
(Note 7)
150
490
ns
max
t
PF
Power Failure Response Time
(Note 8)
40
90
ns
max
t
RESET
Reset Delay
C
EXT
= 0.01 F
100
ms
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is in-
tended to be functional, but specific performance is not guaranteed. For guaranteed specifications and the test conditions, see the Electrical Characteristics.
Note 2: Human body model, 1.5 k
in series with 100 pF. Machine model. 200
in series with 100 pF.
3
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AC Electrical Characteristics
(Continued)
Note 3: Supply current measured at pins 1, 2, and 3. The 4.7 k
pull-up resistor on pin 7 is not tied to V
DD
in this measurement.
Note 4: PCI Specifications Revision 2.1, Section 4.2.1.1 and Section 4.3.2.
Note 5: PCI Specifications Revision 2.1, Section 4.2.2.1 and Section 4.3.2.
Note 6: PCI Specifications Revision 2.1 and Section 4.3.2.
Note 7: PCI Specifications Revision 2.1, Section 4.3.2. The response time is measured individually with
750 mV of overdrive applied to pin 2 then
600 mV of over-
drive applied to pin 3 and taking the worst number of the four measurements.
Note 8: PCI Specifications Revision 2.1, Section 4.3.2. The power failure response time is measured with a signal changing from 5V to 3V applied to pin 2 and a
3.3V DC applied to pin 3.
LMC6953 Timing Diagram
DS012846-3
Note: t
RESET
, t
D
and t
PF
are not to scale.
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4
Typical Performance Characteristics
Unless otherwise specified, T
A
= 25C
Supply Current vs Temperature
DS012846-4
Output Voltage vs Supply Voltage
DS012846-12
Power-Up Supply Voltage
vs Temperature
DS012846-9
V
H5
vs Temperature
DS012846-5
V
L5
vs Temperature
DS012846-6
V
H3.3
vs Temperature
DS012846-7
5
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