19-1122; Rev 3; 12/05
4-Pin µP Voltage Monitors with Pin-Selectable
Power-On Reset Timeout Delay
General Description
The MAX821/MAX822 microprocessor (µP) supervisory
circuits monitor power supplies in µP and digital sys-
tems. They provide excellent circuit reliability and low
cost by eliminating external components and adjust-
ments when used with 5V-powered or 3V-powered cir-
cuits. The MAX821/MAX822 also provide a power-on
reset timeout delay that is pin selectable to 1ms (max),
20ms (min), or 100ms (min).
These devices perform a single function: they assert a
reset signal whenever the V
CC
supply voltage falls
below a preset threshold, and they keep reset asserted
for the pin-selected reset timeout delay after V
CC
has
risen above the reset threshold. The only difference
between the two devices is that the MAX821 has an
active-low
RESET
output (which is guaranteed to be in
the correct state for V
CC
down to 1V), while the
MAX822 has an active-high RESET output. The reset
comparator is designed to ignore fast transients on
V
CC
. Reset thresholds suitable for operation with a vari-
ety of supply voltages are available.
Low supply current makes the MAX821/MAX822 ideal
for use in portable equipment. These devices come in a
4-pin SOT143 package.
Features
♦
Pin-Selectable, Precision Power-On Reset Delay:
1ms (max), 20ms (min), or 100ms (min)
♦
Precision Monitoring of +3V to +5V Power-Supply
Voltages
♦
2.5µA Supply Current
♦
Guaranteed Over Temperature (-40°C to +125°C)
♦
Guaranteed
RESET
Valid to V
CC
= 1V (MAX821)
♦
Power-Supply Transient Immunity
♦
No External Components
♦
SOT143 Package
MAX821/MAX822
Ordering Information
PART
MAX821LUS-T
NOMINAL V
TH
(V)
TOP MARK*
4.63
AZ_ _
MAX821MUS-T
4.38
BA_ _
MAX821PUS-T
4.00
BM_ _
MAX821TUS-T
3.08
BB_ _
MAX821SUS-T
2.93
BC_ _
MAX821UUS-T
2.78
BL_ _
MAX821RUS-T
2.63
BD_ _
MAX822LUS-T
4.63
BF_ _
MAX822MUS-T
4.38
BG_ _
MAX822TUS-T
3.08
BH_ _
MAX822SUS-T
2.93
BJ_ _
MAX822RUS-T
2.63
BK_ _
* The first two letters in the package top mark identify the part,
while the remaining two letters are the lot-tracking code.
Devices are available in both leaded and lead-free packaging.
Specify lead-free by replacing “-T” with “+T” when ordering.
________________________Applications
Bar-Code Scanners
Computers
Controllers
Intelligent Instruments
Critical µP and µC Power Monitoring
Portable/Battery-Powered Equipment
__________Typical Operating Circuit
Pin Configuration
V
CC
V
CC
TOP VIEW
µP
RESET
INPUT
(RESET) RESET
2
GND
1
4
V
CC
MAX821
MAX822
20ms
100ms
1ms
RESET
(RESET)
GND
MAX821
MAX822
SRT
3
SRT
GND
SOT143
( ) ARE FOR MAX822
( ) ARE FOR MAX822
________________________________________________________________
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.
4-Pin µP Voltage Monitors with Pin-Selectable
Power-On Reset Timeout Delay
MAX821/MAX822
ABSOLUTE MAXIMUM RATINGS
Terminal Voltage (with respect to GND)
V
CC
......................................................................-0.3V to 6.0V
All Other Inputs.......................................-0.3V to (V
CC
+ 0.3V)
Input Current, V
CC
, SRT......................................................20mA
Output Current, RESET or
RESET
.......................................20mA
Continuous Power Dissipation (T
A
= +70°C)
SOT143-4 (derate 4mW/°C above +70°C)...................320mW
Operating Temperature Range .........................-40°C to +125°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10sec) .............................+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
= full range, T
A
= -40°C to +125°C, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
V
CC
Range
SYMBOL
CONDITIONS
T
A
= 0°C to +70°C
T
A
= -40°C to +85°C
MAX82_L/M/P,
V
CC
= 5.5V, I
OUT
= 0
MAX82_R/S/T/U,
V
CC
= 5.5V, I
OUT
= 0
MAX82_L
MAX82_M
MAX82_P
Reset Threshold (Note 1)
V
TH
MAX82_T
MAX82_S
MAX82_U
MAX82_R
Reset Threshold Tempco
V
CC
to Reset Delay (Note 1)
Reset Active Timeout Period
t
RP
V
CC
falling at 1mV/µs
SRT = GND
SRT = V
CC
SRT = unconnected
SRT Input Current (Note 2)
V
IL
SRT Input Threshold
V
IH
V
OPEN
2
SRT = GND
RESET
= low for MAX821,
SRT = V
CC
RESET = high for MAX822
SRT = unconnected
RESET
= low for MAX821,
RESET = high for MAX822
0.5
20
100
-100
100
-1
0.9V
CC
0.5V
CC
1
0.07V
CC
V
µA
T
A
= +25°C
T
A
= T
MIN
to T
MAX
T
A
= +25°C
T
A
= T
MIN
to T
MAX
T
A
= +25°C
T
A
= -40°C to +125°C
T
A
= +25°C
T
A
= -40°C to +125°C
T
A
= +25°C
T
A
= -40°C to +125°C
T
A
= +25°C
T
A
= -40°C to +125°C
T
A
= +25°C
T
A
= -40°C to +125°C
T
A
= +25°C
T
A
= -40°C to +125°C
T
A
= +25°C
T
A
= -40°C to +125°C
4.56
4.50
4.31
4.25
3.97
3.91
3.04
3.00
2.89
2.85
2.74
2.70
2.59
2.55
30
50
0.8
32
160
1
40
200
ms
2.63
2.78
2.93
3.08
4.00
4.38
4.63
1.8
MIN
1.0
1.2
2.5
TYP
MAX
5.5
5.5
7.0
12
5.5
9
4.70
4.75
4.45
4.50
4.04
4.09
3.11
3.15
2.96
3.00
2.81
2.85
2.66
2.70
ppm/°C
µs
V
µA
UNITS
V
Supply Current
I
CC
_______________________________________________________________________________________
4-Pin µP Voltage Monitors with Pin-Selectable
Power-On Reset Timeout Delay
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= full range, T
A
= -40°C to +125°C, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
SRT Input Capacitance
(Note 3) (see
Setting
the Reset Timeout Delay
section)
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
MAX821/MAX822
Internal
20
pF
MAX821L/M/P only, I
SINK
= 3.2mA,
V
CC
= V
TH(MIN)
MAX821R/S/T/U only, I
SINK
= 1.2mA,
V
CC
= V
TH(MIN)
T
A
= 0°C to +70°C,
V
CC
≥
1V
T
A
= -40°C to +85°C,
V
CC
≥
1.2V
V
CC
-1.5
0.8V
CC
0.4
0.3
0.3
V
0.3
V
OL
RESET
Output Voltage
(MAX821)
I
SINK
= 50µA
V
OH
MAX821L/M/P only, I
SOURCE
= 800µA,
V
CC
≥
V
TH(MAX)
MAX821R/S/T/U only, I
SOURCE
= 500µA,
V
CC
≥
V
TH(MAX)
MAX822L/M only, I
SINK
= 3.2mA,
V
CC
= V
TH(MAX)
MAX822R/S/T only, I
SINK
= 1.2mA,
V
CC
= V
TH(MAX)
I
SOURCE
= 150µA, 1.4V
≤
V
CC
≤
V
TH(MIN)
0.4
0.3
0.8V
CC
V
RESET Output Voltage
(MAX822)
V
OL
V
OH
Note 1:
RESET
output for MAX821; RESET output for MAX822.
Note 2:
During reset active timeout period only.
Note 3:
Guaranteed by design.
__________________________________________Typical Operating Characteristics
(T
A
= +25°C, unless otherwise noted.)
RESET TIMEOUT PERIOD
vs. TEMPERATURE
MAX 821/822 TOC-04
RESET TIMEOUT PERIOD
vs. TEMPERATURE
MAX 821/822 TOC-05
RESET TIMEOUT PERIOD
vs. TEMPERATURE
SRT = UNCONNECTED
RESET TIMEOUT PERIOD (ms)
175
170
165
160
155
150
MAX 821/822 TOC-06
1.0
SRT = GND
RESET TIMEOUT PERIOD (ms)
0.9
36
SRT = V
CC
RESET TIMEOUT PERIOD (ms)
35
34
33
32
31
30
180
0.8
0.7
0.6
-40
-20
0
20
40
60
80
100
TEMPERATURE (°C)
-40
-20
0
20
40
60
80
100
-40
-20
0
20
40
60
80
100
TEMPERATURE (°C)
TEMPERATURE (°C)
_______________________________________________________________________________________
3
4-Pin µP Voltage Monitors with Pin-Selectable
Power-On Reset Timeout Delay
MAX821/MAX822
____________________________Typical Operating Characteristics (continued)
(T
A
= +25°C, unless otherwise noted.)
MAX82_R/S/T POWER-DOWN RESET DELAY
vs. TEMPERATURE
MAX 821/822 TOC-02
MAX82_L/M POWER-DOWN RESET DELAY
vs. TEMPERATURE
POWER-DOWN RESET DELAY (µs)
V
CC
FALLING AT 1mV/µs
50
40
30
20
10
0
MAX 821/822 TOC-03
45
POWER-DOWN RESET DELAY (µs)
40
35
30
25
20
15
10
5
0
-40
-20
0
20
40
60
80
V
CC
FALLING AT 10mV/µs
V
CC
FALLING AT 1mV/µs
60
V
CC
FALLING AT 10mV/µs
100
-40
-20
0
20
40
60
80
100
TEMPERATURE (°C)
TEMPERATURE (°C)
NORMALIZED SUPPLY
CURRENT vs. TEMPERATURE
MAX 821/822 TOC-01
NORMALIZED RESET THRESHOLD
vs. TEMPERATURE
NORMALIZED RESET THRESHOLD (V)
MAX 821/822 TOC-07
1.10
NORMALIZED SUPPLY CURRENT (µA)
1.003
1.002
1.001
1.000
0.999
0.998
0.997
1.05
1.00
0.95
0.90
-40
-20
0
20
40
60
80
100
TEMPERATURE (°C)
-40
-20
0
20
40
60
80
100
TEMPERATURE (°C)
______________________________________________________________Pin Description
PIN
MAX821
MAX822
1
NAME
GND
RESET
Ground
Active-Low Reset Output.
RESET
is low while V
CC
is below the reset threshold. It remains
low for the reset timeout period after the reset condition is terminated. The reset timeout
period is determined by the SRT input.
Active-High Reset Output. RESET is high while V
CC
is below the reset threshold. It remains
high for the reset timeout period after the reset condition is terminated. The reset timeout
period is determined by the SRT input.
Set Reset Timeout Input. Connect to GND for 1ms (max) delay; connect to V
CC
for 20ms
(min) delay; leave unconnected for 100ms (min) delay.
Supply Voltage
FUNCTION
1
2
–
–
3
4
4
2
RESET
3
4
SRT
V
CC
_______________________________________________________________________________________
4-Pin µP Voltage Monitors with Pin-Selectable
Power-On Reset Timeout Delay
_______________Detailed Description
A microprocessor’s (µP’s) reset input starts the µP in a
known state. These
µP
supervisory circuits assert reset
to prevent code-execution errors during power-up,
power-down, or brownout conditions. They also provide
a reset timeout delay that is pin programmable to 1ms
(max), 20ms (min), or 100ms (min). This feature allows
flexibility in designing bar-code scanners, hand-held
devices, and other applications that require quick or
nonstandard power-up times.
The MAX821’s
RESET
output is guaranteed to be a
logic low for V
CC
> 1V. Once V
CC
exceeds the reset
threshold, an internal timer keeps
RESET
low for the
reset timeout period, as determined by the Set Reset
Timeout (SRT) input. See the
Setting the Reset Timeout
Delay
section.
If a brownout condition occurs (V
CC
dips below the
reset threshold),
RESET
goes low. Any time V
CC
goes
below the reset threshold, the internal timer resets to
zero, and
RESET
goes low. The internal timer begins
counting after V
CC
returns above the reset threshold,
and
RESET
remains low for the reset timeout period.
The MAX822 has an active-high RESET output that is
the inverse of the MAX821’s
RESET
output.
MAXIMUM TRANSIENT DURATION (µs)
T
A
= +25°C
250
200
150
100
50
0
1
10
100
1000
RESET COMPARATOR OVERDRIVE, V
TH
-V
CC
(mV)
MAX821/822 FIG-01
MAX821/MAX822
Reset Output
300
Figure 1. Maximum Transient Duration Without Causing a
Reset Pulse vs. Comparator Overdrive
__________Applications Information
Negative-Going V
CC
Transients
While designed to issue a reset to the microprocessor
(µP) during power-up, power-down, and brownout con-
ditions, the MAX821/MAX822 are relatively immune to
short-duration, negative-going V
CC
transients (glitches).
Figure 1 shows the maximum transient duration vs. reset
comparator overdrive for which the MAX821/MAX822
typically do not generate a reset pulse. This graph was
generated using a negative-going pulse applied to V
CC
,
starting above the actual reset threshold and ending
below it by the magnitude indicated (reset comparator
overdrive). The graph indicates the typical maximum
pulse width a negative-going V
CC
transient may have
without causing a reset pulse to be issued. As the mag-
nitude of the transient increases (goes farther below the
reset threshold), the maximum allowable pulse width
decreases. Typically, for the MAX821/MAX822, a V
CC
transient that goes 100mV below the reset threshold and
lasts 12µs or less will not cause a reset pulse to be
issued. A 0.1µF capacitor mounted as close as possible
to V
CC
can provide additional transient immunity, if
desired.
Setting the Reset Timeout Delay
Use the three-level Set Reset Timeout (SRT) input to set
the reset timeout delay. Connect SRT to GND for a 1ms
(max) delay; connect it to V
CC
for a 20ms (min) delay;
or leave it unconnected for a 100ms (min) delay.
If you choose to drive the SRT pin with an external sig-
nal, make sure the signal source can charge/discharge
the capacitance on SRT quickly enough (<500µs) to
avert an unintended reset timeout delay.
To ensure proper operation when selecting the 100ms
timeout (SRT = unconnected), minimize capacitive
loading on the SRT pin (< 200pF). Excessive capacitive
loading can select an unintended faster timeout mode.
Reset Threshold Accuracy
The MAX821/MAX822 are designed to meet their worst-
case specifications over their entire operating tempera-
ture range. Choose a reset threshold guaranteed to
assert at a voltage below the power supply’s regulation
range and above the minimum specified operating volt-
age range for the system’s ICs.
_______________________________________________________________________________________
5
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