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MAX6340UK29+ |MAX6340UK29MAXIMN/a368avaiLow-Power, SC70/SOT µP Reset Circuits with Capacitor-Adjustable Reset Timeout Delay
MAX6423US26+TMAXIMN/a417avaiLow-Power, SC70/SOT µP Reset Circuits with Capacitor-Adjustable Reset Timeout Delay
MAX6423XS16MAXIMN/a30avaiLow-Power, SC70/SOT µP Reset Circuits with Capacitor-Adjustable Reset Timeout Delay
MAX6423XS16+T |MAX6423XS16TMAXIMN/a500avaiLow-Power, SC70/SOT µP Reset Circuits with Capacitor-Adjustable Reset Timeout Delay
MAX6423XS29+TMAXIM Pb-freeN/a35000avaiLow-Power, SC70/SOT µP Reset Circuits with Capacitor-Adjustable Reset Timeout Delay
MAX6424UK21MAXIMN/a910avaiLow-Power, SC70/SOT µP Reset Circuits with Capacitor-Adjustable Reset Timeout Delay
MAX6424UK21-T |MAX6424UK21TMAXIMN/a7102avaiLow-Power, SC70/SOT µP Reset Circuits with Capacitor-Adjustable Reset Timeout Delay
MAX6424UK29+T |MAX6424UK29TMAXN/a2499avaiLow-Power, SC70/SOT µP Reset Circuits with Capacitor-Adjustable Reset Timeout Delay


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MAX6340UK29+-MAX6423US26+T-MAX6423XS16-MAX6423XS16+T-MAX6423XS29+T-MAX6424UK21-MAX6424UK21-T-MAX6424UK29+T
Low-Power, SC70/SOT µP Reset Circuits with Capacitor-Adjustable Reset Timeout Delay
General Description
The MAX6340/MAX6421–MAX6426 low-power micropro-
cessor 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 voltage
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 externally
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
Beneits and 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
Typical Operating Circuit, Selector Guide, and Ordering
Information appear at end of data sheet.

GND
( ) ARE FOR THE MAX6422
VCC14
SRT
MAX6421X
MAX6422X
MAX6423X
SC70

TOP VIEW3
RESET
(RESET)
MAX6340/MAX6421–
MAX6426
Low-Power, SC70/SOT µP Reset Circuits
with Capacitor-Adjustable Reset Timeout Delay

Pin Configurations continued at end of data sheet.
Pin Conigurations
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) .............245mW4-Pin SOT143 (derate 4mW/°C above +70°C) ...........320mW5-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
(VCC = 1V to 5.5V, TA = TMIN to TMAX, unless otherwise specified. Typical values are at VCC = 5V and TA = +25°C.) (Note 1)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS

Supply Voltage RangeVCC1.05.5V
Supply CurrentICC
VCC ≤ 5.0V2.54.2VCC ≤ 3.3V1.93.4
VCC ≤ 2.0V1.62.5
VCC Reset Threshold AccuracyVTHTA = +25°C VTH - 1.5% VTH + 1.5%VTA = -40°C to +125°C VTH - 2.5% VTH + 2.5%
HysteresisVHYST4 x VTHmV
VCC to Reset DelaytRDVCC falling at 1mV/µs 80µs
Reset Timeout PeriodtRPCSRT = 1500pF3.004.3755.75msCSRT = 00.275
VSRT Ramp CurrentIRAMPVSRT = 0 to 0.65V; VCC = 1.6V to 5V240nA
VSRT Ramp ThresholdVTH-RAMPVCC = 1.6V to 5V (VRAMP rising)0.65V
RAMP Threshold HysteresisVRAMP falling threshold33mV
RESET Output Voltage LowVOL
VCC ≥ 1.0V, ISINK = 50µA0.3VCC ≥ 2.7V, ISINK = 1.2mA0.3
VCC ≥ 4.5V, ISINK = 3.2mA0.4
RESET Output Voltage High,
Push-PullVOH
VCC ≥ 1.8V, ISOURCE = 200µA0.8 x VCCVCC ≥ 2.25V, ISOURCE = 500µA0.8 x VCC
VCC ≥ 4.5V, ISOURCE = 800µA0.8 x VCC
RESET Output Leakage Current,
Open-DrainILKGVCC > VTH, reset not asserted1.0µA
RESET Output Voltage HighVOH
VCC ≥ 1.0V, ISOURCE = 1µA0.8 x VCCVCC ≥ 1.8V, ISOURCE = 150µA0.8 x VCC
VCC ≥ 2.7V, ISOURCE = 500µA0.8 x VCC
VCC ≥ 4.5V, ISOURCE = 800µA0.8 x VCC
RESET Output Voltage LowVOL
VCC ≥ 1.8V, ISINK = 500µA0.3VCC ≥ 2.7V, ISINK = 1.2mA0.3
VCC ≥ 4.5V, ISINK = 3.2mA0.4
MAX6340/MAX6421–
MAX6426
Low-Power, SC70/SOT µP Reset Circuits
with Capacitor-Adjustable Reset Timeout Delay
Electrical Characteristics

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.
Absolute Maximum Ratings
(VCC = 5V, CSRT = 1500pF, TA = +25°C, unless otherwise noted.)
NORMALIZED RESET THRESHOLD
vs. TEMPERATURE
MAX6421/26 toc08
TEMPERATURE (°C)
NORMALIZED RESET THRESHOLD
POWER-UP/POWER-DOWN
CHARACTERISTIC

MAX6421/26 toc07
1V/div
1V/div
VCC
RESET
VTH = 1.6V
400s/div
VCC TO RESET DELAY
vs. TEMPERATURE (VCC FALLING)

MAX6421/26 toc06
TO RESET DELAY S
TEMPERATURE (°C)
VCC FALLING AT 1mVs
MAXIMUM TRANSIENT DURATION
vs. RESET THRESHOLD OVERDRIVE
MAX6421/26 toc05
RESET THRESHOLD OVERDRIVE (mV)
TRANSIENT DURATION (s)
RESET OCCURS
ABOVE THE CURVE
VTH = 2.95V
RESET TIMEOUT PERIOD
vs. TEMPERATURE

MAX6421/26 toc04
RESET TIMEOUT PERIOD (
TEMPERATURE (°C)
CSRT = 0
RESET TIMEOUT PERIOD
vs. TEMPERATURE
MAX6421/26 toc03
TEMPERATURE (°C)
RESET TIMEOUT PERIOD (ms)
CSRT = 1500pF
10,000
RESET TIMEOUT PERIOD vs. CSRT
MAX6421/26 toc02
CSRT (nF)
RESET TIMEOUT PERIOD (ms)
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX6421/26 toc01
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (
TA = +25°C
TA = +125°C
TA = -40°C
MAX6340/MAX6421–
MAX6426
Low-Power, SC70/SOT µP Reset Circuits
with Capacitor-Adjustable Reset Timeout Delay
Typical Operating Characteristics
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 superviso-
ry circuits provide the reset logic to prevent code-execu-
tion 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 capaci-
tor-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 resistor
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 supply-
ing all input current and leakage paths connected to the
RESET line. A 10kΩ to 100kΩ pullup 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
Figure 1. MAX6340/MAX6423/MAX6425/MAX6426 Open-Drain
RESET Output Allows Use with Multiple Supplies
PIN
NAMEFUNCTIONMAX6340
MAX6421
MAX6422
MAX6423
MAX6424
MAX6425MAX6426
SOT23SOT143SC70SOT23SOT23
3351SRT
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 farads1232, 3GNDGround——4—N.C.Not Internally Connected. Can be connected to GND2125VCCSupply Voltage and Reset Threshold Monitor Input44RESET
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——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
SRTRESET
TIMEOUT
GND
RESET
LASER-TRIMMED
RESISTORS
VCC
3.3V
10kΩ
5.0V
SYSTEM
MAX6340/MAX6421–
MAX6426
Low-Power, SC70/SOT µP Reset Circuits
with Capacitor-Adjustable Reset Timeout Delay
Pin Description
CSRT = (tRP - 275µs) / (2.73 5 106)
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-go-
ing 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 magnitude
indicated (reset-threshold overdrive). As the magnitude of
the transient decreases (farther below the reset thresh-
old), 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-sinking
(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; 100kΩ is large enough not to load
RESET and small enough to pull RESET to ground. For
Figure 2. Wired-OR Reset Circuit
VDD
VCC
MAX6340
MAX6423
MAX6425
MAX6426
RESET
GND
OPEN-DRAIN
LOGIC
RESET
10kΩ
MAX6340/MAX6421–
MAX6426
Low-Power, SC70/SOT µP Reset Circuits
with Capacitor-Adjustable Reset Timeout Delay
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 routed 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.
Table 1. Reset Threshold Voltage Suffix

Figure 4. Ensuring RESET Valid to VCC = 0
Figure 3. Ensuring RESET Valid to VCC = 0
SUFFIXMINTYPMAX
1.5361.5751.6141.6231.6651.7071.7551.8001.8451.8531.9001.9481.9502.0002.0502.0482.1002.1532.1332.1882.2432.3132.3132.3712.3402.4002.4602.4382.5002.5632.5592.6252.6912.6332.7002.7682.7302.8002.8702.8522.9252.9982.9253.0003.0752.9983.0753.1523.1203.2003.2803.2183.3003.3833.3153.4003.4853.4133.5003.5583.5103.6003.6903.6083.7003.7933.7053.8003.8953.8033.9003.9983.9004.0004.1003.9984.1004.2034.0954.2004.3054.1934.3004.4084.2664.3754.4844.3884.5004.6134.5094.6254.7414.5834.7004.8184.6804.8004.9204.7784.9005.0234.8755.0005.125
MAX6422
GND
VCC
VCC
RESET
100k
MAX6421
MAX6424
GND
VCC
VCC
RESET
100k
MAX6340/MAX6421–
MAX6426
Low-Power, SC70/SOT µP Reset Circuits
with Capacitor-Adjustable Reset Timeout Delay
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