General Description
The MAX6340/MAX6421–MAX6426 low-power micro-
processor supervisor circuits monitor system voltages
from 1.6V to 5V. These devices perform a single function:
they assert a reset signal whenever the VCC supply volt-
age falls below its reset threshold. The reset output
remains asserted for the reset timeout period after VCC
rises above the reset threshold. The reset timeout is exter-
nally set by a capacitor to provide more flexibility.
The MAX6421/MAX6424 have an active-low, push-
pull reset output. The MAX6422 has an active-high,
push-pull reset output and the MAX6340/MAX6423/
MAX6425/MAX6426 have an active-low, open-drain
reset output. The MAX6421/MAX6422/MAX6423 are
offered in 4-pin SC70 or SOT143 packages. The
MAX6340/MAX6424/MAX6425/MAX6426 are available
in 5-pin SOT23-5 packages.
Applications
Portable Equipment
Battery-Powered Computers/Controllers
Automotive
Medical Equipment
Intelligent Instruments
Embedded Controllers
Critical µP Monitoring
Set-Top Boxes
Computers
Features
Monitor System Voltages from 1.6V to 5V
Capacitor-Adjustable Reset Timeout Period
Low Quiescent Current (1.6µA typ)
Three RESET Output Options
Push-Pull RESET
Push-Pull RESET
Open-Drain RESET
Guaranteed Reset Valid to VCC = 1V
Immune to Short VCC Transients
Small 4-Pin SC70, 4-Pin SOT143, and 5-Pin SOT23
Packages
MAX6340 Pin Compatible with LP3470
MAX6424/MAX6425 Pin Compatible with
NCP300–NCP303, MC33464/MC33465,
S807/S808/S809, and RN5VD
MAX6426 Pin Compatible with PST92XX
MAX6340/MAX6421–MAX6426
Low-Power, SC70/SOT µP Reset Circuits with
Capacitor-Adjustable Reset Timeout Delay
________________________________________________________________ Maxim Integrated Products 1
Ordering Information
GND
( ) ARE FOR THE MAX6422
VCC 14
SRT
MAX6421X
MAX6422X
MAX6423X
SC70
TOP VIEW
23
RESET
(RESET)
Pin Configurations
19-2440; Rev 4; 12/05
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Selector Guide appears at end of data sheet.
PART TEMP RANGE PIN-PACKAGE
MAX6340UK_ _-T -40°C to +125°C 5 SOT23-5
MAX6421XS_ _-T -40°C to +125°C 4 SC70-4
MAX6421US_ _-T -40°C to +125°C 4 SOT143-4
MAX6422XS_ _-T -40°C to +125°C 4 SC70-4
MAX6422US_ _-T -40°C to +125°C 4 SOT143-4
MAX6423XS_ _-T -40°C to +125°C 4 SC70-4
MAX6423US_ _-T -40°C to +125°C 4 SOT143-4
MAX6424UK_ _-T -40°C to +125°C 5 SOT23-5
MAX6425UK_ _-T -40°C to +125°C 5 SOT23-5
MAX6426UK_ _-T -40°C to +125°C 5 SOT23-5
Note: The MAX6340/MAX6421–MAX6426 are available with fac-
tory-trimmed reset thresholds from 1.575V to 5.0V in approxi-
mately 0.1V increments. Insert the desired nominal reset
threshold suffix (from Table 1) into the blanks. There are 50 stan-
dard versions with a required order increment of 2500 pieces.
Sample stock is generally held on standard versions only (see
Standard Versions Table). Required order increment is 10,000
pieces for nonstandard versions. Contact factory for availability.
All devices are available in tape-and-reel only.
Devices are available in both leaded and lead-free packaging.
Specify lead-free by replacing "-T" with "+T" when ordering.
Pin Configurations continued at end of data sheet.
Typical Operating Circuit appears at end of data sheet.
MAX6340/MAX6421–MAX6426
Low-Power, SC70/SOT µP Reset Circuits with
Capacitor-Adjustable Reset Timeout Delay
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VCC = 1V to 5.5V, TA= TMIN to TMAX, unless otherwise specified. Typical values are at VCC = 5V and TA= +25°C.) (Note 1)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
All Voltages Referenced to GND
VCC ........................................................................-0.3V to +6.0V
SRT, RESET, RESET (push-pull).................-0.3V to (VCC + 0.3V)
RESET (open drain)...............................................-0.3V to +6.0V
Input Current (all pins)......................................................±20mA
Output Current (RESET, RESET) ......................................±20mA
Continuous Power Dissipation (TA= +70°C)
4-Pin SC70 (derate 3.1mW/°C above +70°C)..............245mW
4-Pin SOT143 (derate 4mW/°C above +70°C).............320mW
5-Pin SOT23 (derate 7.1mW/°C above +70°C)............571mW
Operating Temperature Range .........................-40°C to +125°C
Storage Temperature Range .............................-65°C to +150°C
Junction Temperature......................................................+150°C
Lead Temperature (soldering, 10s) .................................+300°C
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Supply Voltage Range VCC 1.0 5.5 V
VCC 5.0V 2.5 4.2
VCC 3.3V 1.9 3.4Supply Current ICC
VCC 2.0V 1.6 2.5
µA
TA = +25°C VTH - 1.5% VTH + 1.5%
VCC Reset Threshold Accuracy VTH TA = -40°C to +125°C VTH - 2.5% VTH + 2.5% V
Hysteresis VHYST 4 x VTH mV
VCC to Reset Delay tRD VCC falling at 1mV/µs 80 µs
CSRT = 1500pF 3.00 4.375 5.75
Reset Timeout Period tRP CSRT = 0 0.275 ms
VSRT Ramp Current IRAMP VSRT = 0 to 0.65V; VCC = 1.6V to 5V 240 nA
VSRT Ramp Threshold VTH-RAMP VCC = 1.6V to 5V (VRAMP rising) 0.65 V
RAMP Threshold Hysteresis VRAMP falling threshold 33 mV
VCC 1.0V, ISINK = 50µA 0.3
VCC 2.7V, ISINK = 1.2mA 0.3RESET Output Voltage Low VOL
VCC 4.5V, ISINK = 3.2mA 0.4
V
VCC 1.8V, ISOURCE = 200µA 0.8 x VCC
VCC 2.25V, ISOURCE = 500µA 0.8 x VCC
RESET Output Voltage High,
Push-Pull VOH
VCC 4.5V, ISOURCE = 800µA 0.8 x VCC
V
RESET Output Leakage Current,
Open-Drain ILKG VCC > VTH, reset not asserted 1.0 µA
VCC 1.0V, ISOURCE = 1µA 0.8 x VCC
VCC 1.8V, ISOURCE = 150µA 0.8 x VCC
VCC 2.7V, ISOURCE = 500µA 0.8 x VCC
RESET Output Voltage High VOH
VCC 4.5V, ISOURCE = 800µA 0.8 x VCC
V
VCC 1.8V, ISINK = 500µA 0.3
VCC 2.7V, ISINK = 1.2mA 0.3
RESET Output Voltage Low VOL
VCC 4.5V, ISINK = 3.2mA 0.4
V
Note 1: Devices production tested at +25°C. Overtemperature limits are guaranteed by design.
MAX6340/MAX6421–MAX6426
Low-Power, SC70/SOT µP Reset Circuits with
Capacitor-Adjustable Reset Timeout Delay
_______________________________________________________________________________________ 3
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
021 3456
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX6421/26 toc01
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (µA)
TA = +25°C
TA = +125°C
TA = -40°C
0.1
1
100
10
1000
10,000
0.001 0.10.01 1 10 100 1000
RESET TIMEOUT PERIOD vs. CSRT
MAX6421/26 toc02
CSRT (nF)
RESET TIMEOUT PERIOD (ms)
4.10
4.20
4.15
4.25
4.30
-50 0-25 25 50 75 100 125
RESET TIMEOUT PERIOD
vs. TEMPERATURE
MAX6421/26 toc03
TEMPERATURE (°C)
RESET TIMEOUT PERIOD (ms)
CSRT = 1500pF
RESET TIMEOUT PERIOD
vs. TEMPERATURE
MAX6421/26 toc04
200
250
350
300
500
550
450
400
600
RESET TIMEOUT PERIOD (µs)
-50 0 25-25 50 75 100 125
TEMPERATURE (°C)
CSRT = 0
0
50
25
100
75
150
125
175
0 400200 600 800 1000
MAXIMUM TRANSIENT DURATION
vs. RESET THRESHOLD OVERDRIVE
MAX6421/26 toc05
RESET THRESHOLD OVERDRIVE (mV)
TRANSIENT DURATION (µs)
RESET OCCURS
ABOVE THE CURVE
VTH = 2.95V
VCC TO RESET DELAY
vs. TEMPERATURE (VCC FALLING)
MAX6421/26 toc06
80
90
110
100
140
150
130
120
160
VCC TO RESET DELAY (µs)
-50 0 25-25 50 75 100 125
TEMPERATURE (°C)
VCC FALLING AT 1mVµs
POWER-UP/POWER-DOWN
CHARACTERISTIC
MAX6421/26 toc07
1V/div
1V/div
VCC
RESET
VTH = 1.6V
400µs/div
0.994
0.998
0.996
1.002
1.000
1.004
1.006
-50 25 50-25 0 75 100 125
NORMALIZED RESET THRESHOLD
vs. TEMPERATURE
MAX6421/26 toc08
TEMPERATURE (°C)
NORMALIZED RESET THRESHOLD
Typical Operating Characteristics
(VCC = 5V, CSRT = 1500pF, TA = +25°C, unless otherwise noted.)
MAX6340/MAX6421–MAX6426
Low-Power, SC70/SOT µP Reset Circuits with
Capacitor-Adjustable Reset Timeout Delay
4 _______________________________________________________________________________________
Detailed Description
Reset Output
The reset output is typically connected to the reset input
of a µP. A µP’s reset input starts or restarts the µP in a
known state. The MAX6340/MAX6421–MAX6426 µP
supervisory circuits provide the reset logic to prevent
code-execution errors during power-up, power-down,
and brownout conditions (see Typical Operating
Characteristics).
RESET changes from high to low whenever VCC drops
below the threshold voltage. Once VCC exceeds the
threshold voltage, RESET remains low for the capacitor-
adjustable reset timeout period.
The MAX6422 active-high RESET output is the inverse
logic of the active-low RESET output. All device outputs
are guaranteed valid for VCC > 1V.
The MAX6340/MAX6423/MAX6425/MAX6426 are open-
drain RESET outputs. Connect an external pullup resis-
tor to any supply from 0 to 5.5V. Select a resistor value
large enough to register a logic low when RESET is
asserted and small enough to register a logic high
while supplying all input current and leakage paths
connected to the RESET line. A 10kto 100kpullup
is sufficient in most applications.
Selecting a Reset Capacitor
The reset timeout period is adjustable to accommodate
a variety of µP applications. Adjust the reset timeout
period (tRP) by connecting a capacitor (CSRT) between
SRT and ground. Calculate the reset timeout capacitor
as follows:
Pin Description
PIN
MAX6340
MAX6421
MAX6422
MAX6423
MAX6424
MAX6425 MAX6426
SOT23 SOT143 SC70 SOT23 SOT23
NAME FUNCTION
1 3 3 5 1 SRT
Set Reset Timeout Input. Connect a capacitor between SRT
and ground to set the timeout period. Determine the period as
follows: tRP = 2.73 106 CSRT + 275µs with tRP in seconds
and CSRT in farads.
2 1 2 3 2, 3 GND Ground
3 4 N.C. Not Internally Connected. Can be connected to GND.
42125V
CC Supply Voltage and Reset Threshold Monitor Input
514RESET
RESET changes from high to low whenever VCC drops below
the selected reset threshold voltage. RESET remains low for
the reset timeout period after VCC exceeds the reset
threshold.
44
RESET
RESET changes from low to high whenever VCC drops below
the selected reset threshold voltage. RESET remains high for
the reset timeout period after VCC exceeds the reset
threshold.
MAX6340
MAX6423
MAX6425
MAX6426
VREF
CSRT
SRT RESET
TIMEOUT
N
GND
RESET
LASER-TRIMMED
RESISTORS
VCC
3.3V
10k
5.0V
5V
SYSTEM
Figure 1. MAX6340/MAX6423/MAX6425/MAX6426 Open-Drain
RESET
Output Allows Use with Multiple Supplies
MAX6340/MAX6421–MAX6426
Low-Power, SC70/SOT µP Reset Circuits with
Capacitor-Adjustable Reset Timeout Delay
_______________________________________________________________________________________ 5
CSRT = (tRP - 275µs) / (2.73 106)
where tRP is in seconds and CSRT is in farads.
The reset delay time is set by a current/capacitor-con-
trolled ramp compared to an internal 0.65V reference.
An internal 240nA ramp current source charges the
external capacitor. The charge to the capacitor is
cleared when a reset condition is detected. Once the
reset condition is removed, the voltage on the capacitor
ramps according to the formula: dV/dt = I/C. The CSRT
capacitor must ramp to 0.65V to deassert the reset.
CSRT must be a low-leakage (<10nA) type capacitor;
ceramic is recommended.
Operating as a Voltage Detector
The MAX6340/MAX6421–MAX6426 can be operated in a
voltage detector mode by floating the SRT pin. The reset
delay times for VCC rising above or falling below the
threshold are not significantly different. The reset output is
deasserted smoothly without false pulses.
Applications Information
Interfacing to Other Voltages for Logic
Compatibility
The open-drain outputs of the MAX6340/MAX6423/
MAX6425/MAX6426 can be used to interface to µPs with
other logic levels. As shown in Figure 1, the open-drain
output can be connected to voltages from 0 to 5.5V. This
allows for easy logic compatibility to various µPs.
Wired-OR Reset
To allow auxiliary circuitry to hold the system in reset,
an external open-drain logic signal can be connected
to the open-drain RESET of the MAX6340/MAX6423/
MAX6425/MAX6426, as shown in Figure 2. This config-
uration can reset the µP, but does not provide the reset
timeout when the external logic signal is released.
Negative-Going VCC Transients
In addition to issuing a reset to the µP during power-up,
power-down, and brownout conditions, these supervisors
are relatively immune to short-duration negative-going
transients (glitches). The graph Maximum Transient
Duration vs. Reset Threshold Overdrive in the Typical
Operating Characteristics shows this relationship.
The area below the curve of the graph is the region in
which these devices typically do not generate a reset
pulse. This graph was generated using a negative-
going pulse applied to VCC, starting above the actual
reset threshold (VTH) and ending below it by the magni-
tude indicated (reset-threshold overdrive). As the mag-
nitude of the transient decreases (farther below the
reset threshold), the maximum allowable pulse width
decreases. Typically, a VCC transient that goes 100mV
below the reset threshold and lasts 50µs or less does
not cause a reset pulse to be issued.
Ensuring a Valid RESET or
RESET
Down to VCC = 0
When VCC falls below 1V, RESET/RESET current-sink-
ing (sourcing) capabilities decline drastically. In the
case of the MAX6421/MAX6424, high-impedance
CMOS-logic inputs connected to RESET can drift to
undetermined voltages. This presents no problems in
most applications, since most µPs and other circuitry
do not operate with VCC below 1V.
In those applications where RESET must be valid down
to zero, adding a pulldown resistor between RESET
and ground sinks any stray leakage currents, holding
RESET low (Figure 3). The value of the pulldown resis-
tor is not critical; 100kis large enough not to load
RESET and small enough to pull RESET to ground. For
applications using the MAX6422, a 100kpullup resis-
VDD
VCC
MAX6340
MAX6423
MAX6425
MAX6426
RESET
N
N
GND
OPEN-DRAIN
LOGIC
µP
RESET
10k
Figure 2. Wired-OR Reset Circuit
MAX6340/MAX6421–MAX6426
Low-Power, SC70/SOT µP Reset Circuits with
Capacitor-Adjustable Reset Timeout Delay
6 _______________________________________________________________________________________
tor between RESET and VCC holds RESET high when
VCC falls below 1V (Figure 4). Open-drain RESET ver-
sions are not recommended for applications requiring
valid logic for VCC down to zero.
Layout Consideration
SRT is a precise current source. When developing the
layout for the application, be careful to minimize board
capacitance and leakage currents around this pin.
Traces connected to SRT should be kept as short as
possible. Traces carrying high-speed digital signals
and traces with large voltage potentials should be rout-
ed as far from SRT as possible. Leakage current and
stray capacitance (e.g., a scope probe) at this pin
could cause errors in the reset timeout period. When
evaluating these parts, use clean prototype boards to
ensure accurate reset periods.
MAX6421
MAX6424
GND
VCC
VCC
RESET
100k
Figure 3. Ensuring
RESET
Valid to VCC = 0
MAX6422
GND
VCC
VCC
RESET
100k
Figure 4. Ensuring RESET Valid to VCC = 0
SUFFIX MIN TYP MAX
16 1.536 1.575 1.614
17 1.623 1.665 1.707
18 1.755 1.800 1.845
19 1.853 1.900 1.948
20 1.950 2.000 2.050
21 2.048 2.100 2.153
22 2.133 2.188 2.243
23 2.313 2.313 2.371
24 2.340 2.400 2.460
25 2.438 2.500 2.563
26 2.559 2.625 2.691
27 2.633 2.700 2.768
28 2.730 2.800 2.870
29 2.852 2.925 2.998
30 2.925 3.000 3.075
31 2.998 3.075 3.152
32 3.120 3.200 3.280
33 3.218 3.300 3.383
34 3.315 3.400 3.485
35 3.413 3.500 3.558
36 3.510 3.600 3.690
37 3.608 3.700 3.793
38 3.705 3.800 3.895
39 3.803 3.900 3.998
40 3.900 4.000 4.100
41 3.998 4.100 4.203
42 4.095 4.200 4.305
43 4.193 4.300 4.408
44 4.266 4.375 4.484
45 4.388 4.500 4.613
46 4.509 4.625 4.741
47 4.583 4.700 4.818
48 4.680 4.800 4.920
49 4.778 4.900 5.023
50 4.875 5.000 5.125
Table 1. Reset Threshold Voltage Suffix
MAX6340/MAX6421–MAX6426
Low-Power, SC70/SOT µP Reset Circuits with
Capacitor-Adjustable Reset Timeout Delay
_______________________________________________________________________________________ 7
PART* OUTPUT STAGE TOP MARK
MAX6340UK16-T Open-Drain RESET AEBE
MAX6340UK22-T Open-Drain RESET AEBG
MAX6340UK26-T Open-Drain RESET AEBI
MAX6340UK29-T Open-Drain RESET AEBJ
MAX6340UK46-T Open-Drain RESET AEBM
MAX6421US16-T Push-Pull RESET KADA
MAX6421XS16-T Push-Pull RESET ACU
MAX6421US22-T Push-Pull RESET KADE
MAX6421XS22-T Push-Pull RESET ACY
MAX6421US26-T Push-Pull RESET KADG
MAX6421XS26-T Push-Pull RESET ADA
MAX6421US29-T Push-Pull RESET KADH
MAX6421XS29-T Push-Pull RESET ADB
MAX6421US46-T Push-Pull RESET KADK
MAX6421XS46-T Push-Pull RESET ADE
MAX6422US16-T Push-Pull RESET KADB
MAX6422XS16-T Push-Pull RESET ACV
MAX6422US22-T Push-Pull RESET KADM
MAX6422XS22-T Push-Pull RESET ADG
MAX6422US26-T Push-Pull RESET KADO
MAX6422XS26-T Push-Pull RESET ADI
MAX6422US29-T Push-Pull RESET KADP
MAX6422XS29-T Push-Pull RESET ADJ
MAX6422US46-T Push-Pull RESET KADS
MAX6422XS46-T Push-Pull RESET ADM
Standard Versions Table
*Sample stock is generally held on all standard versions. Contact
factory for availability of nonstandard versions.
PART* OUTPUT STAGE TOP MARK
MAX6423US16-T Open-Drain RESET KADC
MAX6423XS16-T Open-Drain RESET ACW
MAX6423US22-T Open-Drain RESET KADU
MAX6423XS22-T Open-Drain RESET ADO
MAX6423US26-T Open-Drain RESET KADW
MAX6423XS26-T Open-Drain RESET ADQ
MAX6423US29-T Open-Drain RESET KADX
MAX6423XS29-T Open-Drain RESET ADR
MAX6423US46-T Open-Drain RESET KAEA
MAX6423XS46-T Open-Drain RESET ADU
MAX6424UK16-T Push-Pull RESET ADUF
MAX6424UK22-T Push-Pull RESET ADUK
MAX6424UK26-T Push-Pull RESET ADUM
MAX6424UK29-T Push-Pull RESET ADUN
MAX6424UK46-T Push-Pull RESET ADUQ
MAX6425UK16-T Open-Drain RESET ADUG
MAX6425UK22-T Open-Drain RESET ADUS
MAX6425UK26-T Open-Drain RESET ADUU
MAX6425UK29-T Open-Drain RESET ADUV
MAX6425UK46-T Open-Drain RESET ADUY
MAX6426UK16-T Open-Drain RESET ADUH
MAX6426UK22-T Open-Drain RESET ADVA
MAX6426UK26-T Open-Drain RESET ADVC
MAX6426UK29-T Open-Drain RESET ADVD
MAX6426UK46-T Open-Drain RESET ADVG
MAX6421
MAX6424
VREF
CSRT
SRT RESET
TIMEOUT
GND
RESET
LASER-TRIMMED
RESISTORS
VCC
VCC
µP
RESET
Typical Operating Circuit
MAX6340/MAX6421–MAX6426
Low-Power, SC70/SOT µP Reset Circuits with
Capacitor-Adjustable Reset Timeout Delay
8 _______________________________________________________________________________________
PART PUSH-PULL RESET PUSH-PULL RESET OPEN-DRAIN RESET PIN-PACKAGE
MAX6340 5 SOT23
MAX6421 4 SOT143/SC70
MAX6422 4 SOT143/SC70
MAX6423 4 SOT143/SC70
MAX6424 5 SOT23
MAX6425 5 SOT23
Selector Guide
VCC
N.C.
1 5 SRT
MAX6424
MAX6425
SOT23
TOP VIEW
2
34
RESET
GND
GND
15V
CC
MAX6426
SOT23
2
34
SRT
GND RESET
VCC
N.C.
15SRT
MAX6340
SOT23
2
34
RESET
GND
GND
VCC
14
SRT
MAX6421U
MAX6422U
MAX6423U
SOT143
23
RESET
(RESET)
Pin Configurations (continued)
Chip Information
TRANSISTOR COUNT: 295
PROCESS: BiCMOS
MAX6340/MAX6421–MAX6426
Low-Power, SC70/SOT µP Reset Circuits with
Capacitor-Adjustable Reset Timeout Delay
_______________________________________________________________________________________ 9
SC70, 4L.EPS
PACKAGE OUTLINE, 4L SC70
21-0098
1
1
C
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
MAX6340/MAX6421–MAX6426
Low-Power, SC70/SOT µP Reset Circuits with
Capacitor-Adjustable Reset Timeout Delay
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
10 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2005 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.
SOT-143 4L.EPS
E
1
1
21-0052
PACKAGE OUTLINE, SOT-143, 4L
SOT-23 5L .EPS
E
1
1
21-0057
PACKAGE OUTLINE, SOT-23, 5L
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)