19-2625; Rev 2; 12/05
Ultra-Low-Voltage µP Reset Circuits and
Voltage Detectors
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 V
CC
.
The MAX6841–MAX6845 assert a reset signal whenev-
er the V
CC
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 V
CC
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 V
CC
.
The low supply current (5.7µA) and small package
(SOT23-5) make the MAX6841–MAX6845 ideal for use
in portable equipment.
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 V
CC
= 0.55V
(Active Low)
♦
Manual Reset Input
♦
Immune to Short V
CC
Transients
♦
Space-Saving 5-Pin SOT23 Package
MAX6841–MAX6845
Ordering Information
PART
MAX6841_UKD_-T
MAX6842_UKD_-T
MAX6843UKD_-T
MAX6844UKD_-T
MAX6845UKD_-T
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
5 SOT23-5
5 SOT23-5
5 SOT23-5
5 SOT23-5
5 SOT23-5
Applications
Computers
Controllers
Intelligent Instruments
Critical µP and µC Power Monitoring
Portable/Battery-Powered Equipment
Telecom/Networking Equipment
Basestations
Servers/Workstations
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.
Pin Configurations
TOP VIEW
RESET 1
GND 2
5 V
CC
RESET
1
(RESET)
GND 2
4 MR
RESET IN 3
5 V
CC
MAX6841
MAX6842
MAX6843
MAX6844
MAX6845
4 MR
Selector Guide and Typical Operating Circuit appear at end
of data sheet.
RESET 3
SOT23-5
SOT23-5
( ) ARE FOR 6844
________________________________________________________________
Maxim Integrated Products
1
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.
Ultra-Low-Voltage µP Reset Circuits and
Voltage Detectors
MAX6841–MAX6845
ABSOLUTE MAXIMUM RATINGS
Terminal Voltage (with respect to GND)
V
CC
.......................................................................-0.3V to +6V
MR,
RESET IN,
RESET
(open-drain).........................-0.3V to +6V
Push-Pull
RESET
and RESET .....................-0.3V to (V
CC
+ 0.3V)
Input Current (all pins) ........................................................20mA
Output Current (RESET,
RESET).........................................20mA
Continuous Power Dissipation (T
A
= +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
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.
ELECTRICAL CHARACTERISTICS
(V
CC
= +0.55V to +1.8V, T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at T
A
= +25°C.) (Note 1)
PARAMETER
Supply Voltage Range
SYMBOL
V
CC
CONDITIONS
MAX6843/MAX6845
MAX6841/MAX6842/MAX6844 (Note 2)
V
CC
= 0.9V, no load, reset not asserted
Supply Current
I
CC
V
CC
= 1.5V, no load, reset not asserted
V
CC
= 1.8V, no load, reset not asserted
I
Reset Threshold
(V
CC
Falling)
H
V
TH
G
F
E
D, T
A
= 0°C to +85°C
RESET IN Threshold
RESET IN Leakage Current
Reset Threshold Hysteresis
V
CC
or RESET IN to Reset Delay
V
RSTIN
I
RSTIN
V
HYS
V
CC
falling, step signal from (V
TH
+ 10%)
to (V
TH
- 10%) within 1µs
D0 (voltage detector)
D1
Reset Active Timeout Period
t
RP
D2
D3
D4
MR
Input Voltage (Note 3)
MR
Minimum Input Pulse Width
MR
Glitch Rejection
MR
to Reset Delay
MR
Pullup Resistance to V
CC
V
IL
V
IH
MR
driven from V
CC
to 0 (Note 3)
MR
driven from V
CC
to 0 (Note 3)
MR
driven from V
CC
to 0 (Note 3)
10
0.7
×
V
CC
1
150
500
20
26
1
20
140
1120
MAX6843/MAX6844/MAX6845 (Note 3)
1.350
1.275
1.080
1.020
0.810
0.765
181.2
-25
0.75
150
0.15
1.5
30
210
1680
2
40
280
2240
0.3
×
V
CC
V
µs
ns
ns
kΩ
ms
MIN
0.55
0.75
5.7
7.3
8.1
1.388
1.313
1.110
1.050
0.833
0.788
187.4
TYP
MAX
1.80
1.80
20
20
20
1.425
1.350
1.140
1.080
0.855
0.810
191.5
+25
mV
nA
%V
TH
µs
V
µA
UNITS
V
2
_______________________________________________________________________________________
Ultra-Low-Voltage µP Reset Circuits and
Voltage Detectors
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= +0.55V to +1.8V, T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at T
A
= +25°C.) (Note 1)
PARAMETER
Open-Drain
RESET
Output
Voltage
Open-Drain
RESET
Output
Leakage Current
SYMBOL
V
OL
I
LKG
V
OL
Push-Pull
RESET
Output Voltage
V
OH
CONDITIONS
V
CC
≥
0.55V, I
SINK
= 10µA, reset asserted
V
CC
≥
0.83V, I
SINK
= 80µA, reset asserted
V
CC
> V
TH
, reset not asserted
V
CC
≥
0.55V, I
SINK
= 10µA, reset asserted
V
CC
≥
0.83V, I
SINK
= 80µA, reset asserted
V
CC
≥
0.83V, I
SOURCE
= 40µA, reset not
asserted
V
CC
≥
0.75V, I
SOURCE
= 10µA, reset
asserted
V
OH
Push-Pull RESET Output Voltage
V
OL
V
CC
≥
0.83V, I
SOURCE
= 40µA, reset
asserted
V
CC
≥
0.83V, I
SINK
= 80µA, reset not
asserted
0.8
×
V
CC
0.8
×
V
CC
0.8
×
V
CC
0.2
×
V
CC
V
MIN
TYP
MAX
0.2
×
V
CC
0.2
×
V
CC
1
0.2
×
V
CC
0.2
×
V
CC
V
UNITS
V
µA
MAX6841–MAX6845
Note 1:
100% production tested at +25°C. Overtemperature limits are guaranteed by design.
Note 2:
The active-low output
RESET
has V
CC(MIN)
= 0.55V (MAX6841/MAX6842).
Note 3:
For V
CC
> 0.788V, T
A
= 0°C to +85°C, and for V
CC
> 0.833V, T
A
= -40°C to +85°C.
Typical Operating Characteristics
(V
CC
= 1.5V, T
A
= +25°C, unless otherwise noted.)
SUPPLY CURRENT
vs. TEMPERATURE
MAX6841-45 toc01
POWER-DOWN RESET DELAY
vs. TEMPERATURE
MAX6841-45 toc02
NORMALIZED RESET TIMEOUT PERIOD
vs. TEMPERATURE
NORMALIZED RESET TIMEOUT PERIOD
MAX6841-45 toc03
9
8
SUPPLY CURRENT (µA)
7
6
5
4
3
2
1
0
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
V
CC
= 1.5V
V
CC
= 0.9V
V
CC
= 1.8V
350
POWER-DOWN RESET DELAY (µs)
300
250
200
150
100
V
OD
= 100mV
50
V
OD
= OVERDRIVE (mV)
0
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
V
OD
= 10mV
V
OD
= 20mV
1.06
1.04
1.02
1.00
0.98
0.96
0.94
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
D4 OPTION
D2 OPTION
D3 OPTION
_______________________________________________________________________________________
3
Ultra-Low-Voltage µP Reset Circuits and
Voltage Detectors
MAX6841–MAX6845
Typical Operating Characteristics (continued)
(V
CC
= 1.5V, T
A
= +25°C, unless otherwise noted.)
NORMALIZED V
CC
RESET THRESHOLD
vs. TEMPERATURE
MAX6841-45 toc04
NORMALIZED RESET IN THRESHOLD
vs. TEMPERATURE
NORMALIZED RESET IN THRESHOLD
MAX6841-45 toc05
POWER-UP/POWER-DOWN
CHARACTERISTICS (MAX6843AUKD3)
MAX6841-45 toc06
1.015
V
TH
= 0.833V
NORMALIZED V
CC
RESET THRESHOLD
1.010
1.005
1.000
0.995
0.990
0.985
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
1.015
1.010
1.005
1.000
0.995
0.990
0.985
-40
-20
0
20
40
60
80
V
CC
1V/div
RESET
1V/div
200ms/div
TEMPERATURE (°C)
Pin Description
FUNCTION
PIN
MAX6841
MAX6842
MAX6843
MAX6845
MAX6844
NAME
1
—
—
RESET
Push-Pull (MAX6841) or Open-Drain (MAX6842) Active-Low Reset Output.
RESET
changes from high to low when V
CC
drops below the selected reset threshold or
MR
is pulled low.
RESET
remains low for the reset timeout period after V
CC
exceeds the device reset threshold and
MR
is released high.
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 V
CC
) 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.
Ground
Push-Pull Active-High Reset Output. RESET changes from low to high when V
CC
input drops below the selected reset threshold or
MR
is pulled low. RESET
remains high for the reset timeout period after V
CC
exceeds the device reset
threshold and
MR
is released high.
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 V
CC
).
RESET remains high for the reset timeout period after RESET IN exceeds the reset
threshold.
—
1
—
2
2
2
GND
3
—
—
RESET
—
—
1
—
3
3
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
RESET IN typical threshold is 187.4mV (referenced to V
CC
). The MAX6843/MAX6844/
MAX6845 assert a reset signal when the V
CC
to RESET IN differential falls below
its threshold voltage.
MR
V
CC
Active-Low Manual Reset Input. Internal 20kΩ pullup to V
CC
. 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 V
CC
if unused.
Supply Voltage. Monitored supply for the MAX6841/MAX6842.
4
5
4
5
4
5
4
_______________________________________________________________________________________
Ultra-Low-Voltage µP Reset Circuits and
Voltage Detectors
MAX6841–MAX6845
Functional Diagrams
MR
MR
V
CC
MR
PULLUP
V
REF
MANUAL
RESET
DETECT
MAX6841
MAX6842
V
CC
MR
PULLUP
V
REF
= 187.4mV
RESET IN
MANUAL
RESET
DETECT
MAX6843
MAX6844
MAX6845
RESET
TIMEOUT
PERIOD
RESET
OUTPUT
RESET
RESET
RESET
TIMEOUT
PERIOD
RESET
OUTPUT
RESET
RESET
GND
GND
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 V
CC
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 V
CC
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.
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 V
CC
. 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 V
CC
. As V
CC
falls, the voltage at
V
CC
R1
V
CC
RESET IN
R2
MAX6843
MAX6844
MAX6845
MR
R1 =
R2
V
CC-TH
-1
V
REF
GND
RESET
(RESET)
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-
( ) ARE FOR
MAX6844
WHERE V
REF
= 187.4mV (WITH RESPECT TO V
CC
) AND
V
CC-TH
IS THE V
CC
THRESHOLD.
Figure 1. Setting the Adjustable Threshold Externally
5
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