General Description
The MAX6841–MAX6845 microprocessor (µP) supervi-
sory circuits monitor ultra-low-voltage power supplies in
µP and digital systems. They provide excellent circuit
reliability at low cost by eliminating external compo-
nents and adjustments when used with +0.9V to +1.5V
systems. Factory-trimmed reset thresholds are avail-
able for the MAX6841/MAX6842. The MAX6843/
MAX6844/MAX6845 provide a RESET IN input, allowing
the user to externally adjust the reset threshold. The
MAX6841–MAX6845 family features a debounced man-
ual reset input (MR). The reset comparator is designed
to ignore fast transients on VCC.
The MAX6841–MAX6845 assert a reset signal whenev-
er the VCC supply voltage declines below a preset or
adjustable threshold or whenever manual reset (MR) is
asserted. Reset remains asserted for a fixed timeout
delay after VCC has risen above the reset threshold and
when manual reset is deasserted. Five timeout periods
are available for each part: 150µs (voltage detector ver-
sion), 1.5ms, 30ms, 210ms, and 1.68s (typ).
The MAX6841/MAX6843 have an active-low push-pull
reset output. The MAX6841/MAX6842/MAX6844 have
an active-high push-pull reset output, and the
MAX6842/MAX6845 have an active-low open-drain
reset output. The active-low open-drain reset output
requires a pullup resistor that can be connected to a
voltage from 0 to VCC.
The low supply current (5.7µA) and small package
(SOT23-5) make the MAX6841–MAX6845 ideal for use
in portable equipment.
Applications
Computers
Controllers
Intelligent Instruments
Critical µP and µC Power Monitoring
Portable/Battery-Powered Equipment
Telecom/Networking Equipment
Basestations
Servers/Workstations
Features
♦Factory-Set Reset Threshold Voltages for
Monitoring Supplies from 0.9V to 1.5V
(MAX6841/MAX6842)
♦Adjustable Threshold RESET IN
(MAX6843/MAX6844/MAX6845)
♦Low Power Consumption: 5.7µA (typ)
♦±2.5% Reset Threshold Accuracy
Over Temperature
♦Five Timeout Periods: 150µs (Voltage Detector
Version), 1.5ms, 30ms, 210ms, and 1.68s
♦Available in Three Output Configurations
Push-Pull RESET
Push-Pull RESET
Open-Drain RESET
♦Guaranteed Reset Valid to VCC = 0.55V
(Active Low)
♦Manual Reset Input
♦Immune to Short VCC Transients
♦Space-Saving 5-Pin SOT23 Package
MAX6841–MAX6845
Ultra-Low-Voltage µP Reset Circuits and
Voltage Detectors
________________________________________________________________ Maxim Integrated Products 1
Ordering Information
19-2625; Rev 2; 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 and Typical Operating Circuit appear at end
of data sheet.
PART TEMP RANGE PIN-PACKAGE
MAX6841_UKD_-T
-40°C to +85°C5 SOT23-5
MAX6842_UKD_-T
-40°C to +85°C5 SOT23-5
MAX6843UKD_-T
-40°C to +85°C5 SOT23-5
MAX6844UKD_-T
-40°C to +85°C5 SOT23-5
MAX6845UKD_-T
-40°C to +85°C5 SOT23-5
GND
RESET
15V
CC
MAX6841
MAX6842
SOT23-5
TOP VIEW
2
34
RESET
MR
( ) ARE FOR 6844
GND
RESET IN
15V
CC
MAX6843
MAX6844
MAX6845
SOT23-5
2
34
RESET
(RESET)
MR
Pin Configurations
Note: Insert desired suffix letter (from the Threshold Suffix Guide
and the Active Timeout Period tables) into the blanks to com-
plete the part number. For example, the MAX6842GUKD1 has a
reset threshold of 1.11V and a typical reset timeout period of
1.5ms. Sample stock is generally available on standard versions
only (see the Standard Versions table). Standard versions
require a minimum order increment of 2.5k units. Nonstandard
versions must be ordered in 10k-unit increments. Contact factory
for availability. All parts are offered 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.
MAX6841–MAX6845
Ultra-Low-Voltage µP Reset Circuits and
Voltage Detectors
2_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VCC = +0.55V to +1.8V, TA= -40°C to +85°C, unless otherwise noted. Typical values are at 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.
Terminal Voltage (with respect to GND)
VCC .......................................................................-0.3V to +6V
MR, RESET IN, RESET (open-drain).........................-0.3V to +6V
Push-Pull RESET and RESET .....................-0.3V to (VCC + 0.3V)
Input Current (all pins) ........................................................20mA
Output Current (RESET, RESET).........................................20mA
Continuous Power Dissipation (TA= +70°C)
5-Pin SOT23 (derate 7.1mW/°C above +70°C)............571mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX
UNITS
MAX6843/MAX6845
0.55 1.80
Supply Voltage Range VCC MAX6841/MAX6842/MAX6844 (Note 2)
0.75 1.80
V
VCC = 0.9V, no load, reset not asserted 5.7 20
VCC = 1.5V, no load, reset not asserted 7.3 20
Supply Current ICC
VCC = 1.8V, no load, reset not asserted 8.1 20
µA
I
1.350 1.388 1.425
H
1.275 1.313 1.350
G
1.080 1.110 1.140
F
1.020 1.050 1.080
E
0.810 0.833 0.855
Reset Threshold
(VCC Falling) VTH
D, TA = 0°C to +85°C
0.765 0.788 0.810
V
RESET IN Threshold VRSTIN MAX6843/MAX6844/MAX6845 (Note 3)
181.2 187.4 191.5
mV
RESET IN Leakage Current IRSTIN -25
+25
nA
Reset Threshold Hysteresis VHYS
0.75
%VTH
VCC or RESET IN to Reset Delay
VCC falling, step signal from (VTH + 10%)
to (VTH - 10%) within 1µs
150
µs
D0 (voltage detector)
0.15
D1 1 1.5 2
D2 20 30 40
D3
140 210
280
Reset Active Timeout Period tRP
D4
1120 1680 2240
ms
VIL
0.3 × VCC
MR Input Voltage (Note 3) VIH 0.7 × VCC
V
MR Minimum Input Pulse Width MR driven from VCC to 0 (Note 3) 1 µs
MR Glitch Rejection MR driven from VCC to 0 (Note 3)
150
ns
MR to Reset Delay MR driven from VCC to 0 (Note 3)
500
ns
MR Pullup Resistance to VCC 10 20 26 kΩ
MAX6841–MAX6845
Ultra-Low-Voltage µP Reset Circuits and
Voltage Detectors
_______________________________________________________________________________________ 3
Note 1: 100% production tested at +25°C. Overtemperature limits are guaranteed by design.
Note 2: The active-low output RESET has VCC(MIN) = 0.55V (MAX6841/MAX6842).
Note 3: For VCC > 0.788V, TA= 0°C to +85°C, and for VCC > 0.833V, TA= -40°C to +85°C.
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +0.55V to +1.8V, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
TYP
MAX
UNITS
VCC ≥ 0.55V, ISINK = 10µA, reset asserted 0.2 × VCC
Open-Drain RESET Output
Voltage VOL VCC ≥ 0.83V, ISINK = 80µA, reset asserted
0.2 × VCC
V
Open-Drain RESET Output
Leakage Current ILKG VCC > VTH, reset not asserted 1 µA
VCC ≥ 0.55V, ISINK = 10µA, reset asserted 0.2 × VCC
VOL VCC ≥ 0.83V, ISINK = 80µA, reset asserted
0.2 × VCC
Push-Pull RESET Output Voltage
VOH VCC ≥ 0.83V, ISOURCE = 40µA, reset not
asserted 0.8 × VCC
V
VCC ≥ 0.75V, ISOURCE = 10µA, reset
asserted 0.8 × VCC
VOH VCC ≥ 0.83V, ISOURCE = 40µA, reset
asserted 0.8 × VCC
Push-Pull RESET Output Voltage
VOL VCC ≥ 0.83V, ISINK = 80µA, reset not
asserted
0.2 × VCC
V
Typical Operating Characteristics
(VCC = 1.5V, TA= +25°C, unless otherwise noted.)
SUPPLY CURRENT
vs. TEMPERATURE
MAX6841-45 toc01
TEMPERATURE (°C)
SUPPLY CURRENT (µA)
6040200-20
1
2
3
4
5
6
7
8
9
0
-40 80
VCC = 1.8V
VCC = 1.5V
VCC = 0.9V
POWER-DOWN RESET DELAY
vs. TEMPERATURE
MAX6841-45 toc02
TEMPERATURE (°C)
POWER-DOWN RESET DELAY (µs)
6040200-20
50
100
150
200
250
300
350
0
-40 80
VOD = 10mV
VOD = 20mV
VOD = 100mV
VOD = OVERDRIVE (mV)
NORMALIZED RESET TIMEOUT PERIOD
vs. TEMPERATURE
MAX6841-45 toc03
TEMPERATURE (°C)
NORMALIZED RESET TIMEOUT PERIOD
6040200-20
0.96
0.98
1.00
1.02
1.04
1.06
0.94
-40 80
D2 OPTION
D3 OPTION
D4 OPTION
MAX6841–MAX6845
Ultra-Low-Voltage µP Reset Circuits and
Voltage Detectors
4_______________________________________________________________________________________
Pin Description
Typical Operating Characteristics (continued)
(VCC = 1.5V, TA= +25°C, unless otherwise noted.)
NORMALIZED VCC RESET THRESHOLD
vs. TEMPERATURE
MAX6841-45 toc04
TEMPERATURE (°C)
NORMALIZED VCC RESET THRESHOLD
6040200-20
0.990
0.995
1.000
1.005
1.010
1.015
0.985
-40 80
VTH = 0.833V
NORMALIZED RESET IN THRESHOLD
vs. TEMPERATURE
MAX6841-45 toc05
TEMPERATURE (°C)
NORMALIZED RESET IN THRESHOLD
6040200-20
0.990
0.995
1.000
1.005
1.010
1.015
0.985
-40 80
POWER-UP/POWER-DOWN
CHARACTERISTICS (MAX6843AUKD3)
MAX6841-45 toc06
200ms/div
VCC
1V/div
RESET
1V/div
PIN
MAX6841
MAX6842
MAX6843
MAX6845 MAX6844
NAME
FUNCTION
1——
Push-Pull (MAX6841) or Open-Drain (MAX6842) Active-Low Reset Output. RESET
changes from high to low when VCC drops below the selected reset threshold or
MR is pulled low. RESET remains low for the reset timeout period after VCC
exceeds the device reset threshold and MR is released high.
—1—
RESET
Push-Pull (MAX6843) or Open-Drain (MAX6845) Active-Low Reset Output. RESET
changes from high to low when RESET IN drops below the 187.4mV reset
threshold (referenced to VCC) or MR is pulled low. RESET remains low for the
reset timeout period after RESET IN exceeds the reset threshold and MR is
released high.
222GND Ground
3——
Push-Pull Active-High Reset Output. RESET changes from low to high when VCC
input drops below the selected reset threshold or MR is pulled low. RESET
remains high for the reset timeout period after VCC exceeds the device reset
threshold and MR is released high.
—— 1
RESET
Push-Pull Active-High Reset Output. RESET changes from low to high when the
RESET IN input drops below the 187.4mV reset threshold (referenced to VCC).
RESET remains high for the reset timeout period after RESET IN exceeds the reset
threshold.
—3 3
RESET IN
Adjustable Reset Input. High-impedance input for reset comparator. Connect this
pin to an external resistive-divider network to set the reset threshold voltage; the
typical threshold is 187.4mV (referenced to VCC). The MAX6843/MAX6844/
MAX6845 assert a reset signal when the VCC to RESET IN differential falls below
its threshold voltage.
444MR
Active-Low Manual Reset Input. Internal 20kΩ pullup to VCC. Pull low to force a
reset. Reset remains active as long as MR is low and for the reset timeout period
after MR goes high. Leave unconnected or connect to VCC if unused.
555V
CC Supply Voltage. Monitored supply for the MAX6841/MAX6842.
Detailed Description
Reset Output
A microprocessor’s (µP’s) reset input starts the µP in a
known state. The MAX6841–MAX6845 assert a reset dur-
ing power-up, power-down, and brownout conditions.
When the VCC supply voltage falls below a preset thresh-
old (MAX6841/MAX6842) or RESET IN falls below the
adjustable threshold (MAX6843/MAX6844/MAX6845),
reset asserts and stays asserted for a fixed timeout delay
(Table 2) after VCC or RESET IN has risen above the
reset threshold. The MAX6841–MAX6845 are available
with five typical timeout options for each part: 150µs
(voltage detector), 1.5ms, 30ms, 210ms, and 1.68s.
The MAX6841/MAX6842 have two reset outputs
(RESET and RESET); one is the inverse of the other.
The MAX6841 has one active-high push-pull output and
one active-low push-pull output. The MAX6842 has one
active-high push-pull output and one active-low open-
drain output. The MAX6843 features an active-low
push-pull output. The MAX6844 features an active-
high push-pull output, and the MAX6845 has an active-
low open-drain output stage. Connect a pullup resistor
from the open-drain RESET output to any voltage
between 0 and 6V.
Manual Reset Input
Many µP-based systems require a manual reset capa-
bility, allowing the operator, a test technician, or exter-
nal logic circuitry to initiate a reset. Reset remains
asserted while MR is low, and for a fixed timeout delay
after MR returns high. This input has an internal 20kΩ
pullup resistor, so it can be left open if it is not used.
MR can be driven with CMOS logic level or with open-
drain/collector outputs. To create a manual reset func-
tion, connect a normally open momentary switch from
MR to ground; external debounce circuitry is not
required. If MR is driven from long cables or the device
is used in a noisy environment, connect a 0.1µF capac-
itor from MR to ground to provide additional noise
immunity.
RESET IN
The MAX6843/MAX6844/MAX6845 feature a RESET IN
input, which allows users to adjust the reset threshold
voltage. The internal reference voltage is 187.4mV with
respect to VCC. An external resistive-divider network
can be used to set voltage monitoring thresholds, as
shown in Figure 1. The resistive-divider network must
be referenced to VCC. As VCC falls, the voltage at
MAX6841–MAX6845
Ultra-Low-Voltage µP Reset Circuits and
Voltage Detectors
_______________________________________________________________________________________ 5
VCC
RESET
OUTPUT
RESET
RESET
TIMEOUT
PERIOD
VREF
MANUAL
RESET
DETECT
GND
MR
MR
PULLUP
RESET
MAX6841
MAX6842
Functional Diagrams
VCC
RESET
OUTPUT
RESET
TIMEOUT
PERIOD
VREF = 187.4mV
MANUAL
RESET
DETECT
GND
MR
MR
PULLUP
RESET
RESET
RESET IN
MAX6843
MAX6844
MAX6845
MAX6843
MAX6844
MAX6845
VCC
GND
RESET IN
MR
RESET
(RESET)
( ) ARE FOR
MAX6844
R1 = R2
R2
R1
VCC-TH
VREF - 1
WHERE VREF = 187.4mV (WITH RESPECT TO VCC) AND
VCC-TH IS THE VCC THRESHOLD.
VCC
Figure 1. Setting the Adjustable Threshold Externally
MAX6841–MAX6845
RESET IN decreases. The MAX6843/MAX6844/
MAX6845 assert a reset when the voltage at RESET IN
falls below the RESET IN threshold (VRSTIN). The low-
leakage current at RESET IN allows for relatively large-
value resistors to be used, which reduces power
consumption. For example, for VCC-TH = 0.9V, if R2 =
100kΩ, then R1 = 26.3kΩ.
Applications Information
VCC Falling Transients
The MAX6841–MAX6845 are relatively immune to short-
duration falling VCC transients (glitches). Figure 2
shows typical transient duration vs. reset comparator
overdrive, for which the MAX6841–MAX6845 do not
generate a reset pulse. The graph was generated using
a falling pulse applied to VCC, starting 0.1V above the
actual reset threshold and ending below it by the mag-
nitude indicated (reset comparator overdrive). The
graph indicates the maximum pulse width that a falling
VCC transient can have without causing a reset pulse.
As the magnitude of the transient increases (goes fur-
ther below the reset threshold), the maximum allowable
pulse width decreases. A 0.1µF bypass capacitor
mounted as close as possible to the VCC pin provides
additional transient immunity.
Ensuring a Valid Reset Output
Down to VCC = 0
When VCC falls below 0.55V, the MAX6841/MAX6843
push-pull RESET output no longer sinks current; it
becomes an open circuit. Therefore, high-impedance
CMOS-logic inputs connected to RESET can drift to
undetermined voltages. This presents no problem in
most applications, because most µP and other circuitry
are inoperative with VCC lower than 0.55V. However, in
applications in which RESET must be valid down to 0,
adding a pulldown resistor to RESET causes any stray
leakage currents to flow to ground, holding RESET low
(Figure 3). R3’s value is not critical; 200kΩis large
enough not to load RESET and small enough to pull
RESET to ground.
A 200kΩpullup resistor to VCC is also recommended
for the MAX6841/MAX6842/MAX6844 if push-pull
RESET is required to remain valid for VCC ≤0.75V.
Interfacing to µPs with Bidirectional
Reset Pins
Because the RESET output on the MAX6842/MAX6845
is open drain, these devices interface easily with µPs
that have bidirectional reset pins. Connecting the µP
supervisor’s RESET output directly to the µP’s RESET
pin with a single pullup resistor allows either device to
assert reset (Figure 4).
Ultra-Low-Voltage µP Reset Circuits and
Voltage Detectors
6_______________________________________________________________________________________
MAXIMUM TRANSIENT DURATION
vs. OVERDRIVE
OVERDRIVE VTH - VCC (mV)
MAXIMUM TRANSIENT DURATION (µs)
10
150
200
250
300
350
400
450
500
550
600
100
1 100
RESET OCCURS ABOVE THIS LINE
Figure 2. Maximum Transient Duration vs. Overdrive
MAX6841
MAX6843
VCC
RESET
GND R3
Figure 3.
RESET
Valid to VCC = 0
MAX6842
MAX6845
VCC
VCC
RESET
GND
VCC
RESET
INPUT
GND
µP
Figure 4. Interfacing to Microprocessors with Bidirectional
Reset I/0
Using the MAX6842/MAX6845 Open-Drain
RESET
Output with Multiple Supplies
Generally, the pullup connected to the MAX6842/
MAX6845 connects to the supply voltage being moni-
tored at the IC’s VCC pin. However, some systems use
the open-drain output to level-shift from the monitored
supply to reset circuitry powered by some other supply
(Figure 5). Note that as the MAX6842/MAX6845’s VCC
decreases, so does the IC’s ability to sink current at
RESET. Also, with any pullup, RESET is pulled high as
VCC decays toward 0. The voltage where this occurs
depends on the pullup resistor value and the voltage to
which it is connected.
Chip Information
TRANSISTOR COUNT: 788
PROCESS: BiCMOS
MAX6841–MAX6845
Ultra-Low-Voltage µP Reset Circuits and
Voltage Detectors
_______________________________________________________________________________________ 7
Table 1. Threshold Suffix Guide
MAX6842
MAX6845
VCC
RESET
GND
VCC
RESET
GND
RPULLUP
0.9V
µP
+5.0V
Figure 5. Using the MAX6842/MAX6845 Open-Drain
RESET
Output with Multiple Supplies
SUFFIX RESET THRESHOLD (V)
I1.388
H1.313
G1.110
F1.050
E0.833
D0.788
Table 2. Active Timeout Period Guide
RESET ACTIVE TIMEOUT PERIOD (ms)
SUFFIX
MIN TYP MAX
D0 — 0.15 —
D1 1 1.5 2
D2 20 30 40
D3 140 210 280
D4 1120 1680 2240
Table 3. Standard Versions
DEVICE TOP MARK
MAX6841HUKD0 AEDR
MAX6841HUKD3 AEDS
MAX6841FUKD0 AEDP
MAX6841FUKD3 AEDQ
MAX6841DUKD0 AEDN
MAX6841DUKD3 AEDO
MAX6842HUKD0 AEDX
MAX6842HUKD3 AEDY
MAX6842FUKD0 AEDV
MAX6842FUKD3 AEDW
MAX6842DUKD0 AEDT
MAX6842DUKD3 AEDU
MAX6843UKD0 AEDZ
MAX6843UKD3 AEAV
MAX6844UKD0 AEEB
MAX6844UKD3 AEEC
MAX6845UKD0 AEAX
MAX6845UKD3 AEAY
MAX6841–MAX6845
Ultra-Low-Voltage µP Reset Circuits and
Voltage Detectors
8_______________________________________________________________________________________
Selector Guide
PART
MANUAL RESET
ADJUSTABLE
RESET INPUT
PUSH-PULL
RESET
PUSH-PULL
RESET
OPEN-DRAIN
RESET
MAX6841 ✔—✔✔—
MAX6842 ✔——✔✔
MAX6843 ✔✔✔——
MAX6844 ✔✔—✔—
MAX6845 ✔✔——✔
CORE
SUPPLY
µP
I/O
SUPPLY
VCC
GND
GND
0.9V
RESET
VIN
3.3V
DC/DC
CONVERTER
MAX6842D/E
MR
RESET RESET
PUSHBUTTON
SWITCH
Typical Operating Circuit
MAX6841–MAX6845
Ultra-Low-Voltage µP Reset Circuits and
Voltage Detectors
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 _____________________ 9
©2005 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.
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.)
SOT-23 5L .EPS
E1
1
21-0057
PACKAGE OUTLINE, SOT-23, 5L