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MAX6394
High-Accuracy μP Reset Circuit
General Description
The MAX6394 low-power CMOS microprocessor (μP)
supervisory circuit is designed to monitor power supplies in
μP and digital systems. It offers excellent circuit reliability
by providing 1% accurate thresholds over temperature and
by eliminating external components and adjustments. The
MAX6394 also provides a debounced manual reset input.
This device performs a single function: it asserts a reset
signal whenever the VCC supply voltage falls below a
preset threshold or whenever manual reset is asserted.
RESET remains asserted for an internally programmed
interval (reset timeout period) after VCC has risen above
the reset threshold or manual reset is deasserted. The
MAX6394’s open-drain RESET output can be pulled up
to a voltage higher than VCC.
The MAX6394 comes with factory-trimmed reset threshold
voltages from 2.4V to 4.8V. Preset timeout periods of
0.7ms, 14ms, 105ms, and 826ms are also available. The
device comes in a SOT143 package.
Benefits and Features
●● ±0.6% Threshold Accuracy at TA = +25°C
●● ±1.0% Threshold Accuracy from -40°C to +125°C
●● Small SOT143 Package
●● Open-Drain RESET Output Can Exceed VCC
●● Precision, Factory-Set VCC Reset Thresholds:
Nine Options from 2.4V to 4.8V
●● Four Reset Timeout Periods Available:
0.7ms, 14ms, 105ms, and 826ms (minimum)
●● Immune to Short VCC Transients
●● 5μA Supply Current
●● AEC-Q100 Qualified, Refer to Ordering Information
for Specific /V Part
Ordering Information appears at end of data sheet.
Applications
●●
●●
●●
●●
●●
Computers
Controllers
Intelligent Instruments
Critical μP and μC Power Monitoring
Portable/Battery-Powered Equipment
Pin Configuration
Typical Operating Circuit
VCC
TOP VIEW
+
GND
1
4
VCC
MAX6394
VCC
LASERTRIMMED
RESISTORS
MAX6394
P
RESET
2
3
SOT143
19-3202; Rev 5; 12/19
MR
MR
RESET
CIRCUITRY
GND
RESET
RESET
MAX6394
High-Accuracy μP Reset Circuit
Absolute Maximum Ratings
VCC.......................................................................-0.3V to +6.0V
RESET..................................................................-0.3V to +6.0V
All Other Pins............................................ -0.3V to (VCC + 0.3V)
Input Current (VCC).............................................................20mA
Output Current (RESET).....................................................20mA
Rate of Rise (VCC)..........................................................100V/μs
Continuous Power Dissipation (TA = +70°C)
SOT143 (derate 3.4mW/°C above +70°C)................275.9mW
Operating Temperature Range.......................... -40°C to +125°C
Storage Temperature Range............................. -65°C to +160°C
Lead Temperature (soldering, 10s).................................. +300°C
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.
Package Information
4 SOT23
PACKAGE CODE
U4+1/U4+1A
Outline Number
21-0052
Land Pattern Number
Thermal Resistance, Single-Layer Board
90-0183
Junction to Ambient (qJA)
N/A
Junction to Case (qJC)
Thermal Resistance, Four-Layer Board
N/A
Junction to Ambient (qJA)
290
Junction to Case (qJC)
100
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that
a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the
drawing pertains to the package regardless of RoHS status.
Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-layer board.
For detailed information on package thermal considerations, refer to www.maximintegrated.com/thermal-tutorial.
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Maxim Integrated │ 2
MAX6394
High-Accuracy μP Reset Circuit
Electrical Characteristics
(VCC = +2.4V to +5.5V, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
Operating Voltage Range
SYMBOL
VCC
CONDITIONS
TA = -40°C to +125°C
MIN
VCC = 5.5V, no load (-40°C to +85°C)
VCC Supply Current
ICC
TYP
1.0
5
VCC = 5.5V, no load (-40°C to +125°C)
Reset Threshold Tempco
VTH
VCC = 3.6V, no load (-40°C to +85°C)
Reset Timeout Period
TA = +25°C (see Table 1)
TA = -40°C to +125°C (see Table 2)
VTH 1.0%
12
4
10
VTH
VTH +
0.6%
VTH +
1.0%
60
VCC = falling at 1mV/µs
tRP
V
µA
12
VTH 0.6%
∆VTH/°C
VCC to Reset Delay
UNITS
5.5
15
VCC = 3.6V, no load (-40°C to +125°C)
Reset Threshold (Note 1)
MAX
V
ppm/°C
35
µs
MAX6394US_ _ _D1+T
0.7
1.4
2.0
MAX6394US_ _ _D2-T
14
28
40
MAX6394US_ _ _D3-T
105
200
280
MAX6394US_ _ _D4-T
826
1570
2240
VTH > 4.0V
0.8
ms
MANUAL RESET INPUT
VIL
MR Input Threshold
VIH
VIL
2.4
VTH < 4.0V
0.3 x VCC
VIH
V
0.7 x VCC
MR Minimum Input Pulse
1
µs
MR Glitch Rejection
100
ns
MR to Reset Delay
500
ns
MR Pullup Resistance
RESET Output Voltage
RESET Output Leakage Current
32
VOL
63
100
VCC > 4.25V, ISINK = 3.2mA
0.4
VCC > 2.5V, ISINK = 1.2mA
0.3
VCC > 1.2V, ISINK = 0.5mA
0.3
VCC > 1.0V, ISINK = 80µA
0.3
VCC > VTH, RESET deasserted
1
kΩ
V
µA
Note 1: The MAX6394 monitors VCC through an internal factory-trimmed voltage-divider that programs the nominal reset threshold.
Other thresholds may be available. Contact factory for availability.
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Maxim Integrated │ 3
MAX6394
High-Accuracy μP Reset Circuit
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
VCC = 3V
2
VCC = 1V
-50
-10
10
30
50
70
TA = +25°C
2
TA = -40°C
0
90
0
1
3
2
VTH = 4.63V
30
VTH = 3.00V
20
10
0
5
4
MAX6394 toc03
MAX6394 toc02
3
VCC FALLING AT 1mV/µs
40
-50
-30
-10
30
10
50
70
90
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
NORMALIZED RESET TIMEOUT PERIOD
vs. TEMPERATURE (VCC RISING)
NORMALIZED RESET THRESHOLD
vs. TEMPERATURE (VCC FALLING)
MAXIMUM TRANSIENT DURATION
vs. RESET COMPARATOR OVERDRIVE
1.01
1.00
0.99
0.98
0.97
-50
-30
-10
10
30
50
TEMPERATURE (°C)
70
90
1.004
1.002
1.000
0.998
0.996
0.994
-50
-30
-10
10
30
50
70
TEMPERATURE (°C)
90
100
MAXIMUM TRANSIENT DURATION (µs)
1.02
1.006
MAX6394 toc05
1.03
0.96
TA = +85°C
1
MAX6394 toc04
1.04
-30
4
50
POWER-DOWN RESET DELAY (µs)
3
1
NORMALIZED RESET TIMEOUT PERIOD
SUPPLY CURRENT (µA)
VCC = 5V
4
5
NORMALIZED RESET THRESHOLD
SUPPLY CURRENT (µA)
5
0
6
MAX6394 toc01
6
POWER-DOWN RESET DELAY
vs. TEMPERATURE
TA = +25°C
RESET OCCURS
ABOVE CURVE
80
VTH = 4.63V
60
40
20
VT = 3.00V
0
10
100
1000
RESET COMP. OVERDRIVE, VTH - VCC (mV)
Pin Description
PIN
NAME
FUNCTION
1
GND
2
RESET
Active-Low Open-Drain Output. Connect to an external pullup resistor. Can be pulled up to a voltage higher
than VCC, but less than 6V.
3
MR
Manual Reset Input. A logic-low on MR asserts reset. Reset remains asserted as long as MR is low, and for
the reset timeout period (tRP) after the reset conditions are terminated. Connect to VCC if not used.
4
VCC
Supply Voltage and Reset Threshold Monitor Input
Ground
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MAX6394 toc06
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
SUPPLY CURRENT vs. TEMPERATURE
Maxim Integrated │ 4
MAX6394
High-Accuracy μP Reset Circuit
Detailed Description
+3.3V
Reset Output
A microprocessor’s (μP’s) reset input starts the μP in
a known state. The MAX6394 asserts a reset signal to
prevent code-execution errors during power-up, powerdown, or brownout conditions. RESET is guaranteed to be
a logic-low for VCC > 1V (see the Electrical Characteristics
table). Once VCC exceeds the reset threshold, the internal
timer keeps RESET asserted for the reset timeout period
(tRP); after this interval RESET goes high. If a brownout
condition occurs (monitored voltage dips below its programmed reset threshold), RESET goes low. Any time
VCC dips below the reset threshold, the internal timer
resets to zero and RESET goes low. The internal timer
starts when VCC returns above the reset threshold, and
RESET remains low for the reset timeout period.
The MAX6394’s RESET output structure is a simple opendrain n-channel MOSFET switch. Connect a pullup resistor to any supply in the 0 to +6V range. Select a resistor
value large enough to register a logic-low when RESET
is asserted (see the Electrical Characteristics table), and
small enough to register a logic-high while supplying all
input current and leakage paths connected to the RESET
line. A 10kΩ pullup is sufficient in most applications.
Often, the pullup connected to the MAX6394’s RESET
output connects to the supply voltage monitored at the
IC’s VCC pin. However, some systems may use the opendrain output to level-shift from the monitored supply to
reset circuitry powered by some other supply (Figure 1).
This is one useful feature of an open-drain output. Keep in
mind that as the MAX6394’s VCC decreases below 1V, so
does the IC’s ability to sink current at RESET. Finally, with
any pullup, RESET is pulled high as VCC decays toward
0V. The voltage where this occurs depends on the pullup
resistor value and the voltage to which it connects (see the
Electrical Characteristics table).
Manual-Reset Input
Many μP-based products require manual-reset capability,
allowing the operator, a test technician, or external logic
circuitry to initiate a reset. A logic-low on MR asserts reset.
RESET remains asserted while MR is low, and for the
reset active timeout period after MR returns high.
+5.0V
VCC
10kΩ
MR
RESET
5V SYSTEM
MAX6394
GND
Figure 1. MAX6394 Open-Drain RESET Output Allows Use
with Multiple Supplies
switch from MR to GND to create a manual reset function;
external debounce circuitry is not required. If MR is driven
from long cables or if the device is used in a noisy environment, connecting a 0.1μF capacitor from MR to ground
provides additional noise immunity.
Applications Information
Negative-Going VCC Transients
In addition to issuing a reset to the μP during power-up,
power-down, and brownout conditions, these devices
are relatively immune to short-duration negative-going
transients (glitches). The Typical Operating Characteristics
show the Maximum Transient Duration vs. Reset Threshold
Overdrive, for which reset pulses are not generated. The
graph was produced using negative-going pulses, starting
at VRST max and ending below the programmed reset
threshold by the magnitude indicated (reset threshold
overdrive). The graph shows the maximum pulse width
that a negative-going VCC transient may typically have
without causing a reset pulse to be issued. As the transient
amplitude increases (i.e., goes farther below the reset
threshold), the maximum allowable pulse width decreases.
A 0.1μF bypass capacitor mounted close to VCC provides
additional transient immunity.
Chip Information
TRANSISTOR COUNT: 529
MR has an internal 63kΩ pullup resistor, so it can be left
open if not used. Connect a normally open momentary
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Maxim Integrated │ 5
MAX6394
High-Accuracy μP Reset Circuit
Table 1. ±0.6% of Thresholds
Table 2. ±1% of Thresholds
±0.6% OF THRESHOLD (V)
±1% OF THRESHOLD (V)
SUFFIX
MIN
TYP
MAX
SUFFIX
MIN
TYP
MAX
480
4.771
4.800
4.829
480
4.752
4.800
4.848
470
4.672
4.700
4.728
470
4.653
4.700
4.747
455
4.523
4.550
4.577
455
4.505
4.550
4.596
445
4.423
4.450
4.477
445
4.406
4.450
4.495
317
3.149
3.168
3.187
317
3.136
3.168
3.200
310
3.083
3.102
3.121
310
3.071
3.102
3.133
300
2.985
3.003
3.021
300
2.973
3.003
3.033
294
2.919
2.937
2.955
294
2.908
2.937
2.966
240
2.386
2.400
2.414
240
2.376
2.400
2.424
Timeout Options
MAX (ms)
Standard Versions
Selector Guide
SUFFIX
MIN (ms)
TYP (ms)
D1
0.7
1.4
2
D2
14
28
40
D3
105
200
280
455
D4
826
1570
2240
310
STANDARD VERSIONS
480
D3
240
Note: Samples are generally available in standard versions.
Contact factory for availability of nonstandard versions.
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Maxim Integrated │ 6
MAX6394
High-Accuracy μP Reset Circuit
Ordering Information
TEMPERATURE
RANGE
PINPACKAGE
MAX6394US_ _ _D_+T
-40°C to +125°C
4 SOT143-4
MAX6394US_ _ _D_/V+T
-40°C to +125°C
4 SOT143-4
MAX6394US317D2/V+T
-40°C to +125°C
4 SOT143-4
MAX6394US480D1/V+T
-40°C to +125°C
4 SOT143-4
MAX6394US480D3/V+T
-40°C to +125°C
4 SOT143-4
PART
Note: This device is specified over the -40°C to +125°C operating
temperature range.
+Denotes a lead-free package.
Note: The “_ _ _” is a placeholder for the input voltage thresholds.
Nine threshold options are available. See Tables 1 and 2 for
more information.
Note: The “_” is a placeholder for the timeout option. Four
options are available. See the Timeout Options section for
more information.
Four standard versions are available (see the Standard
Versions Selector Guide section). Samples are generally
available in standard versions. Contact factory for availability of
nonstandard versions.
Note: All devices are available in tape-and-reel only. Tape and
reel is offered in 2.5k increments.
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Maxim Integrated │ 7
MAX6394
High-Accuracy μP Reset Circuit
Revision History
REVISION
NUMBER
REVISION
DATE
PAGES
CHANGED
0
1/08
Initial release
1
12/15
Added lead-free part numbers and added MAX6394US___/V+T
2
3/18
Added Package Information section
3
3/18
Updated Ordering Information and Benefits and Features
4
8/19
Updated Package Information section
2
5
12/19
Updated Chip Information
5
DESCRIPTION
—
1, 2
2
1, 6
For pricing, delivery, and ordering information, please visit Maxim Integrated’s online storefront at https://www.maximintegrated.com/en/storefront/storefront.html.
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits)
shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
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