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LM3722/LM3723/LM3724
5-Pin Microprocessor Reset Circuits
LM3722/LM3723/LM3724 5-Pin Microprocessor Reset Circuits
June 2001
General Description
The LM3722/LM3723/LM3724 microprocessor supervisory
circuits monitor the power supplies in microprocessor and
digital systems. They provide a reset to the microprocessor
during power-up, power-down, brown-out conditions, and
manual reset.
The LM3722/LM3723/LM3724 asserts a reset signal whenever the supply decreases below the factory-programmed
reset threshold for at least 100 ms. The reset signal remains
asserted for 190 ms after V
The LM3722 has anactive-low RESET push-pull output. The
LM3723 has an active-high RESET push-pull output. The
LM3724 has an active-low open-drain RESET output.
Three standard reset voltage options are available, suitable
for monitoring 5V, 3.3V, and 2.5V supply voltages. Additional
reset voltages are also available; contact National Semiconductor for details.
With a low supply current of only 6µA, the
LM3722/LM3723/LM3724 are ideal foruse in portable equipment. The LM3722/LM3723/LM3724 are available in the
5-pin SOT23 package.
rises above the threshold.
CC
Typical Application Circuit
Features
n Precise monitoring of 2.5V, 3.3V, and 5V supply
voltages
n Fully specified over temperature
Industrial: −40˚C to +85˚C
Extended: −40˚C to +125˚C
n 100 ms minimum Power-On Reset pulse width, 190 ms
typical:
Active-Low RESET Output (LM3722)
Active-High RESET Output (LM3723)
Active-Low RESET Open Drain Output (LM3724)
n Guaranteed RESET Output valid for VCC≥ 1V
n Low Supply Current, 6µA typical
n Power supply transient immunity
n Compatible with MAX811/812 applications
Applications
n Microprocessor Systems
n Computers
n Controllers
n Intelligent Instruments
n Portable/Battery-Powered Equipment
20014401
20014437
Connection Diagram
SOT23-5
*
( ) are for LM3723
© 2001 National Semiconductor Corporation DS200144 www.national.com
20014402
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Ordering Information
Industrial Temperature Range (−40˚C to +85˚C):
Reset
Threshold (V)
4.63 LM3722IM5-4.63 LM3722IM5X-4.63 R43B
LM3722/LM3723/LM3724
2.32 LM3722IM5-2.32 LM3722IM5X-2.32 R34B
Reset
Threshold (V)
4.63 LM3723IM5-4.63 LM3723IM5X-4.63 R13B
2.32 LM3723IM5-2.32 LM3723IM5X-2.32 R46B
Reset
Threshold (V)
4.63 LM3724IM5-4.63 LM3724IM5X-4.63 R55B
2.32 LM3724IM5-2.32 LM3724IM5X-2.32 R50B
LM3722 Supplied as
1000 units, tape & reel
LM3723 Supplied as
1000 units, tape & reel
LM3724 Supplied as
1000 units, tape & reel
LM3722 Supplied as
3000 units, tape & reel
LM3723 Supplied as
3000 units, tape & reel
LM3724 Supplied as
3000 units, tape & reel
Package
Top Mark
Package
Top Mark
Package
Top Mark
Package
Type
SOT23-5 MF05A3.08 LM3722IM5-3.08 LM3722IM5X-3.08 R41B
Package
Type
SOT23-5 MF05A3.08 LM3723IM5-3.08 LM3723IM5X-3.08 R11B
Package
Type
SOT23-5 MF05A3.08 LM3724IM5-3.08 LM3724IM5X-3.08 R53B
Extended Temperature Range (−40˚C to +125˚C):
Reset
Threshold (V)
4.63 LM3722EM5-4.63 LM3722EM5X-4.63 R56B
2.32 LM3722EM5-2.32 LM3722EM5X-2.32 R58B
Reset
Threshold (V)
4.63 LM3723EM5-4.63 LM3723EM5X-4.63 R59B
2.32 LM3723EM5-2.32 LM3723EM5X-2.32 R61B
Reset
Threshold (V)
4.63 LM3724EM5-4.63 LM3724EM5X-4.63 R62B
2.32 LM3724EM5-2.32 LM3724EM5X-2.32 R64B
Custom voltages and improved accuracies are available, subject to minimum orders. Contact your local National Semiconductor Sales Office for information.
LM3722 Supplied as
1000 units, tape & reel
LM3723 Supplied as
1000 units, tape & reel
LM3724 Supplied as
1000 units, tape & reel
LM3722 Supplied as
3000 units, tape & reel
LM3723 Supplied as
3000 units, tape & reel
LM3724 Supplied as
3000 units, tape & reel
Package
Top Mark
Package
Top Mark
Package
Top Mark
Package
Type
SOT23-5 MF05A3.08 LM3722EM5-3.08 LM3722EM5X-3.08 R57B
Package
Type
SOT23-5 MF05A3.08 LM3723EM5-3.08 LM3723EM5X-3.08 R60
Package
Type
SOT23-5 MF05A3.08 LM3724EM5-3.08 LM3724EM5X-3.08 R63B
NSC Package
NSC Package
NSC Package
NSC Package
NSC Package
NSC Package
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Pin Description
PIN NAME FUNCTION
1 GND Ground reference
2 GND Ground reference, device substrate, connect to ground.
RESET
3
LM3722/LM3724
RESET
LM3723
4MR
Active-low output. RESET remains low while V
voltage, and for 190 ms after VCCrises above the reset threshold voltage.
Active-high output. RESET remains high while V
for 190 ms after V
rises above the reset threshold.
CC
Active-low input. Reset is asserted whenever this pin is pulled low and remains
asserted for 190 ms after the MR pin goes high. May be left open.
5VCCSupply Voltage (+5V, +3.3V, or +2.5V, nominal)
Block Diagram
LM3722/LM3723/LM3724 Block Diagram
is below the reset threshold
CC
is below the reset threshold, and
CC
LM3722/LM3723/LM3724
20014435
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Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
V
,MR −0.3V to 6.0V
CC
RESET, RESET
Input Current, V
Output Current, RESET,
LM3722/LM3723/LM3724
RESET Pin
Pin 20mA
CC
−0.3V to (VCC+ 0.3V)
20mA
Continuous Power Dissipation (T
SOT-23 (Note 3) 320mW
Operating Temperature Range
Industrial: −40˚C to +85˚C
Extended: −40˚C to +125˚C
Maximum Junction Temperature 125˚C
Storage Temperature Range −65˚C to +160˚C
Lead Temperature
(soldering, 10sec) +300˚C
= +70˚C)
A
ESD Rating (Note 2) 2kV
Electrical Characteristics
Typical values are at TA= +25˚C. Limits with standard typeface are for TA= +25˚C, and limits in boldface type apply for the
operating temperature range (−40˚C to +85˚C) for LM372_IM5X, and (−40˚C to +125˚C) for LM372_EM5X, unless otherwise
noted. (Note 4)
Symbol Parameter Conditions Min Typ Max Units
V
I
V
V
Tempco
t
t
t
t
V
V
V
V
V
V
V
VCCRange 1.0 5.5 V
CC
LM372 _ -4.63 V
LM372 _ -3.08 V
LM372 _ -2.32 V
CC
Supply Current
= 0A)
(I
LOAD
LM372 _ -4.63
Reset Threshold
TH
LM372 _ -2.32
Reset Threshold
TH
Temperature Coefficient
VCCto Reset Delay (Note 5) VCC=VTHto (VTH− 100mV) 20 µs
RD
Reset Active Timeout Period 100 190 560 ms
RP
MR Minimum Pulse Width 10 µs
MR
MR to Reset Propagation
MD
Delay
MR Glitch Immunity (Note 6)
IH
IL
MR Input Threshold
IH
IL
V
CC
V
CC
-2.32
>
V
>
V
, LM372_ -4.63
TH(MAX)
, LM372_ -3.08, LM372_
TH(MAX)
= 5.5V 8 15 µA
CC
= 3.6V 7 10
CC
= 2.5V 6 10
CC
4.54
4.63 4.72
4.50
3.03
3.08 3.14
3.00
2.27
2.32 2.37
2.25
30 ppm/˚C
2µs
100 ns
2.3
0.7 V
CC
MR Pull-Up Resistance 22 kΩ
RESET Output Voltage Low
OL
(LM3722)
RESET Output Voltage High
OH
(LM3722)
V
CC=VTH
min, I
(LM3722-2.32/3.08)
CC=VTH
min, I
(LM3722-4.63)
>
V
1V, I
CC
V
CC
>
VTHmax, I
SINK
(LM3722-2.32/3.08)
>
VTHmax, I
V
CC
= 1.2mA,
SINK
= 3.2mA,
SINK
= 50µA 0.3
SOURCE
SOURCE
= 500µA,
= 800µA,
0.8V
CC
VCC−1.5
(LM3722-4.63)
RESET Output Voltage Low
OL
(LM3723)
V
CC=VTH
max, I
(LM3723 -2.32/3.08)
V
CC=VTH
max, I
SINK
SINK
= 1.2mA
= 3.2mA
(LM3723 -4.63)
4.75
3.15
2.40
0.8
0.25 V
0.3
0.4
0.3
0.4
VLM372 _ -3.08
V
CC
VV
V
V
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Electrical Characteristics (Continued)
Typical values are at TA= +25˚C. Limits with standard typeface are for TA= +25˚C, and limits in boldface type apply for the
operating temperature range (−40˚C to +85˚C) for LM372_IM5X, and (−40˚C to +125˚C) for LM372_EM5X, unless otherwise
noted. (Note 4)
Symbol Parameter Conditions Min Typ Max Units
V
V
Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which the device operates
correctly. Operating ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions, see the Electrical
Characteristics.
Note 2: The human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin.
Note 3: At elevated temperatures, devices must be derated based on package thermal resistance. The device in the SOT23-5 package must be derated at
4.5mW/˚C at ambient temperatures above 70˚C. The device has internal thermal protection.
Note 4: Production testing done at T
(SQC) methods.
Note 5: RESET Output for LM3722 and LM3724, RESET output for LM3723.
Note 6: Glitches of 100 ns or less typically will not generate a reset pulse.
RESET Output Voltage High
OH
(LM3723)
RESET Output Voltage Low
OL
(LM3724)
I
RESET Output Leakage
IN
Current (LM3724)
0.8V
1.8V
V
CC=VTH
<
<
V
CC
min, I
VTHmin, I
= 1.2 mA
SINK
SOURCE
= 150µA
CC
0.3 V
(LM3724 -2.32/3.08)
V
CC=VTH
min, I
SINK
= 3.2 mA
0.4
(LM3724 -4.63)
>
V
1V, I
CC
>
VTH, RESET = 5.5V
V
CC
= +25˚C. Limits over the operating temperature range are guaranteed through correlation using Statistical Quality Control
A
= 50µA 0.3
SINK
0.5 µA
V
LM3722/LM3723/LM3724
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Typical Performance Characteristics
Supply Current vs V
LM3722/LM3723/LM3724
Reset Timeout vs V
CC
CC
Supply Current vs Temperature
20014403 20014407
Reset Timeout vs Temperature
20014404
Normalized VTHvs Temperature LM3724 VOLvs Current
20014416 20014405
20014408
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Typical Performance Characteristics (Continued)
LM3722/LM3723/LM3724
LM3724 Low V
Characteristics
CC
20014406
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Timing Diagram
LM3722/LM3723/LM3724
Circuit Information
Reset Output
The reset input of a µP initializes the device into a known
state. The LM3722/LM3723/LM3724 microprocessor voltage
monitoring circuits assert a forced reset output to prevent
code execution errors during power-up, power-down, and
brownout conditions.
RESET is guaranteed valid for V
the reset threshold, an internal timer maintains the output for
the reset timeout period. After this interval, reset goes high
and the microprocessor initializes itself into a known state.
The LM3722 and LM3724 offer an active-low RESET; the
LM3723 offers an active-high RESET.
As V
drops below the reset threshold (such as during a
CC
brownout), the reset activates (see the
Transients
section). When VCCagain rises above the reset
threshold, the internal timer starts. Reset holds until V
exceeds the reset threshold for longer than the reset timeout
period. After this time, reset releases.
Additionally, the Manual Reset input (MR) will initiate a
forced reset. See the
Manual Reset Input
The LM3722/LM3723/LM3724 reset outputs ignore short duration glitches on V
mation
section for details.
and MR. See the
CC
≥ 1V.Once VCCexceeds
CC
Negative-Going V
section.
Applications Infor-
CC
CC
20014412
Reset Threshold
The LM3722/LM3723/LM3724 are available with reset voltages of 4.63V, 3.08V, and 2.32V which are suitable for
monitoring 5.0V, 3.3V, and 2.5V supplies respectively. Other
reset thresholds in the 2.20V to 5.0V range, in 10 mV steps,
are available; contact National Semiconductor for details.
Manual Reset Input (MR)
Many µP-based products require a manual reset capability,
allowing the operator to initiate a reset. The MR input is fully
debounced and provides an internal22 kΩ pull-up. When the
MR input is pulled below V
(0.25VCC) for more than 100 ns,
IL
reset is asserted after a typical delay of 2 µs. Reset remains
active as long as MR is held low,andreleases after MR rises
above VIHand the reset timeout period expires. Use MR with
digital logic to assert reset or to daisy chain supervisory
circuits.
Applications Information
Benefits of Precision Reset Thresholds
A microprocessor supply supervisor must provide a reset
output within a predictable range of the supply voltage. A
common threshold range is between 5% and 10% below the
nominal supply voltage.The 4.63V,3.08V and 2.32V options
of the LM3722/LM3723/LM3724 usehighly accurate circuitry
to ensure that the reset threshold occurs only within this
range (for 5.0V, 3.3V and 2.5V supplies).
the standard reset thresholds apply to 5.0V, 3.3V, and 2.5V
nominal supply voltages.
Table 1
shows how
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Applications Information (Continued)
TABLE 1. Monitored Tolerance Table
Reset
Threshold
±
4.63
% 90.8-94.4%
±
3.08
% 91.8-95.2%
±
2.32
% 90.8-94.8%
Ensuring a Valid Reset Output Down to V
When V
falls below 1V, the LM3722 RESET output is
CC
unable to sink the rated current. A high-impedance CMOS
logic input connected to RESET can therefore drift to undetermined voltages. Toprevent this situation, a100kΩ resistor
should be connected from the RESET output to ground, as
shown in
Figure 1
.
A100kΩ pull-up resistor to V
LM3723, if RESET is required to remain valid for V
Supply Voltage
2.5V 3.3V 5.0V
=0V
CC
is also recommended for the
CC
<
1V.
CC
resistor must be small enough so that the leakage current of
all connected devices does not create an excessive voltage
drop when the output is not activated. A resistor value of 100
kΩ will generally suffice.
Negative-Going V
Transients
CC
The LM3722/LM3723/LM3724 are relativelyimmune to short
negative-going transients or glitches on V
the maximum pulse width a negative-going V
CC
.
Figure 2
CC
shows
transient
can have without causing a reset pulse. In general, as the
magnitude of the transient increases, going further below the
threshold, the maximum allowable pulse width decreases.
Typically, a V
transient that goes 125 mV below the reset
CC
threshold and lasts 40 µs or less will not cause a reset pulse.
A 0.1 µF bypass capacitor mounted as close as possible to
the V
pin will provide additional transient rejection.
CC
LM3722/LM3723/LM3724
20014410
FIGURE 1. Circuit for RESET Valid from VCC=0V
Open Drain Output (LM3724)
An open drain output allows easy paralleling of multiple
microprocessor reset circuits without requiring additional
logic gates. Open drain outputs also allow interfacing devices of differing logic levels or families, since the output
pull-up resistor may be connected to any supply voltage up
to 5.5V, regardless of LM3724 V
.
CC
The pull up resistor is calculated so that maximum current
flow into RESET is less than 10 mA when activated. The
20014414
FIGURE 2. Maximum Transient Duration without
Causing a Reset Pulse vs. Reset Comparator
Overdrive
Interfacing to µPs with Bidirectional Reset Pins
Microprocessors with bidirectional reset pins, such as the
Motorola 68HC11 series, can be connected to the LM3722
RESET output. To ensure a correct output on the LM3722
even when the microprocessor reset pin is in the opposite
state, connect a 4.7kΩ resistor between the LM3722 RESET
output and the µP reset pin, as shown in
Figure 3
. Buffer the
LM3722 RESET output to other system components.
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Typical Application Circuits
LM3722/LM3723/LM3724
FIGURE 3. Interfacing to Microprocessors with Bidirectional Reset I/O
20014411
20014422
FIGURE 4. Regulator/Switch with Long-Term Overvoltage Lockout Prevents Overdissipation in Linear Regulator
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Typical Application Circuits (Continued)
FIGURE 5. LM3722 Switch Debouncer
LM3722/LM3723/LM3724
20014431
FIGURE 6. LM3723 Power-On Delay
20014424
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Physical Dimensions inches (millimeters)
unless otherwise noted
5-Lead SOT23-5
For Ordering, refer to Ordering Information table
NS Package Number MF05A
LM3722/LM3723/LM3724 5-Pin Microprocessor Reset Circuits
LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the
labeling, can be reasonably expected to result in a
significant injury to the user.
National Semiconductor
Corporation
Americas
Email: support@nsc.com
www.national.com
National Semiconductor
Europe
Fax: +49 (0) 180-530 85 86
Email: europe.support@nsc.com
Deutsch Tel: +49 (0) 69 9508 6208
English Tel: +44 (0) 870 24 0 2171
Français Tel: +33 (0) 1 41 91 8790
2. A critical component is any component of a life
support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.
National Semiconductor
Asia Pacific Customer
Response Group
Tel: 65-2544466
Fax: 65-2504466
Email: ap.support@nsc.com
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Japan Ltd.
Tel: 81-3-5639-7560
Fax: 81-3-5639-7507
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.
Page 13
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