Maxim MAX822LUS-T 4-pin î¼p voltage monitors with pin-selectable power-on reset timeout delay Datasheet

19-1122; Rev 3; 12/05
4-Pin µP Voltage Monitors with Pin-Selectable
Power-On Reset Timeout Delay
The MAX821/MAX822 microprocessor (µP) supervisory
circuits monitor power supplies in µP and digital systems. They provide excellent circuit reliability and low
cost by eliminating external components and adjustments when used with 5V-powered or 3V-powered circuits. 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 VCC 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
VCC. Reset thresholds suitable for operation with a variety 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.
________________________Applications
Bar-Code Scanners
Computers
Controllers
Intelligent Instruments
Critical µP and µC Power Monitoring
Portable/Battery-Powered Equipment
__________Typical Operating Circuit
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 VCC = 1V (MAX821)
♦ Power-Supply Transient Immunity
♦ No External Components
♦ SOT143 Package
Ordering Information
PART
NOMINAL VTH (V)
TOP MARK*
MAX821LUS-T
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.
Pin Configuration
VCC
VCC
MAX821
MAX822
µP
RESET
(RESET)
20ms
100ms
1ms
TOP VIEW
SRT
GND
4
VCC
3
SRT
MAX821
MAX822
RESET
INPUT
(RESET) RESET
GND
1
2
GND
SOT143
( ) ARE FOR MAX822
( ) ARE FOR MAX822
________________________________________________________________ Maxim Integrated Products
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.
1
MAX821/MAX822
General Description
MAX821/MAX822
4-Pin µP Voltage Monitors with Pin-Selectable
Power-On Reset Timeout Delay
ABSOLUTE MAXIMUM RATINGS
Terminal Voltage (with respect to GND)
VCC ......................................................................-0.3V to 6.0V
All Other Inputs.......................................-0.3V to (VCC + 0.3V)
Input Current, VCC, SRT......................................................20mA
Output Current, RESET or RESET .......................................20mA
Continuous Power Dissipation (TA = +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
(VCC = full range, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
SYMBOL
VCC Range
Supply Current
ICC
CONDITIONS
TA = -40°C to +85°C
1.2
5.5
MAX82_L/M/P,
VCC = 5.5V, IOUT = 0
TA = +25°C
MAX82_R/S/T/U,
VCC = 5.5V, IOUT = 0
TA = +25°C
MAX82_P
MAX82_T
MAX82_S
MAX82_U
MAX82_R
1.8
5.5
4.63
4.70
12
TA = TMIN to TMAX
4.56
TA = -40°C to +125°C
4.50
TA = +25°C
4.31
TA = -40°C to +125°C
4.25
TA = +25°C
3.97
TA = -40°C to +125°C
3.91
TA = +25°C
3.04
TA = -40°C to +125°C
3.00
TA = +25°C
2.89
TA = -40°C to +125°C
2.85
TA = +25°C
2.74
TA = -40°C to +125°C
2.70
TA = +25°C
2.59
TA = -40°C to +125°C
2.55
VCC falling at 1mV/µs
tRP
SRT Input Current (Note 2)
VIL
VIH
VOPEN
V
µA
4.75
4.38
4.45
4.00
4.04
3.08
3.11
4.50
4.09
3.15
2.93
2.96
2.78
2.81
2.63
2.66
2.85
2.70
ppm/°C
50
0.5
V
3.00
0.8
µs
1
SRT = VCC
20
32
40
SRT = unconnected
100
160
200
SRT = GND
RESET = low for MAX821,
SRT = VCC
RESET = high for MAX822
SRT = unconnected
-100
RESET = low for MAX821,
RESET = high for MAX822
UNITS
9
TA = +25°C
SRT = GND
2
7.0
30
VCC to Reset Delay (Note 1)
SRT Input Threshold
2.5
TA = TMIN to TMAX
Reset Threshold Tempco
Reset Active Timeout Period
MAX
5.5
MAX82_M
VTH
TYP
1.0
MAX82_L
Reset Threshold (Note 1)
MIN
TA = 0°C to +70°C
100
-1
ms
µA
1
0.07VCC
V
0.9VCC
0.5VCC
_______________________________________________________________________________________
4-Pin µP Voltage Monitors with Pin-Selectable
Power-On Reset Timeout Delay
(VCC = full range, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
SRT Input Capacitance
(Note 3) (see Setting
the Reset Timeout Delay
section)
VOL
RESET Output Voltage
(MAX821)
MAX
UNITS
Internal
20
pF
MAX821L/M/P only, ISINK = 3.2mA,
VCC = VTH(MIN)
0.4
MAX821R/S/T/U only, ISINK = 1.2mA,
VCC = VTH(MIN)
0.3
ISINK = 50µA
VOH
VOL
RESET Output Voltage
(MAX822)
MIN
TA = 0°C to +70°C,
VCC ≥ 1V
0.3
TA = -40°C to +85°C,
VCC ≥ 1.2V
0.3
V
MAX821L/M/P only, ISOURCE = 800µA,
VCC ≥ VTH(MAX)
VCC -1.5
MAX821R/S/T/U only, ISOURCE = 500µA,
VCC ≥ VTH(MAX)
0.8VCC
MAX822L/M only, ISINK = 3.2mA,
VCC = VTH(MAX)
0.4
MAX822R/S/T only, ISINK = 1.2mA,
VCC = VTH(MAX)
0.3
ISOURCE = 150µA, 1.4V ≤ VCC ≤ VTH(MIN)
VOH
TYP
V
0.8VCC
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
(TA = +25°C, unless otherwise noted.)
0.8
0.7
0.6
SRT = VCC
35
34
33
32
31
-20
0
20
40
60
TEMPERATURE (°C)
80
100
SRT = UNCONNECTED
175
170
165
160
155
150
30
-40
180
MAX 821/822 TOC-06
0.9
36
MAX 821/822 TOC-05
SRT = GND
RESET TIMEOUT PERIOD (ms)
MAX 821/822 TOC-04
1.0
RESET TIMEOUT PERIOD (ms)
RESET TIMEOUT PERIOD
vs. TEMPERATURE
RESET TIMEOUT PERIOD
vs. TEMPERATURE
RESET TIMEOUT PERIOD (ms)
RESET TIMEOUT PERIOD
vs. TEMPERATURE
-40
-20
0
20
40
60
TEMPERATURE (°C)
80
100
-40
-20
0
20
40
60
80
100
TEMPERATURE (°C)
_______________________________________________________________________________________
3
MAX821/MAX822
ELECTRICAL CHARACTERISTICS (continued)
____________________________Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
MAX82_L/M POWER-DOWN RESET DELAY
vs. TEMPERATURE
MAX82_R/S/T POWER-DOWN RESET DELAY
vs. TEMPERATURE
35
VCC FALLING AT 1mV/µs
30
25
20
15
VCC FALLING AT 10mV/µs
10
5
60
MAX 821/822 TOC-03
40
POWER-DOWN RESET DELAY (µs)
MAX 821/822 TOC-02
POWER-DOWN RESET DELAY (µs)
45
VCC FALLING AT 1mV/µs
50
40
30
20
VCC FALLING AT 10mV/µs
10
0
0
-40
-20
0
20
40
60
80
-40
100
-20
0
20
40
60
80
100
TEMPERATURE (°C)
TEMPERATURE (°C)
NORMALIZED RESET THRESHOLD
vs. TEMPERATURE
NORMALIZED SUPPLY
CURRENT vs. TEMPERATURE
1.00
0.95
MAX 821/822 TOC-07
1.05
1.003
NORMALIZED RESET THRESHOLD (V)
MAX 821/822 TOC-01
1.10
NORMALIZED SUPPLY CURRENT (µA)
MAX821/MAX822
4-Pin µP Voltage Monitors with Pin-Selectable
Power-On Reset Timeout Delay
1.002
1.001
1.000
0.999
0.998
0.997
0.90
-40
-20
0
20
40
60
80
100
-40
-20
0
20
40
60
80
100
TEMPERATURE (°C)
TEMPERATURE (°C)
______________________________________________________________Pin Description
PIN
4
NAME
FUNCTION
MAX821
MAX822
1
1
GND
2
–
RESET
Active-Low Reset Output. RESET is low while VCC 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.
–
2
RESET
Active-High Reset Output. RESET is high while VCC 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.
3
3
SRT
Set Reset Timeout Input. Connect to GND for 1ms (max) delay; connect to VCC for 20ms
(min) delay; leave unconnected for 100ms (min) delay.
4
4
VCC
Supply Voltage
Ground
_______________________________________________________________________________________
4-Pin µP Voltage Monitors with Pin-Selectable
Power-On Reset Timeout Delay
If a brownout condition occurs (VCC dips below the
reset threshold), RESET goes low. Any time VCC goes
below the reset threshold, the internal timer resets to
zero, and RESET goes low. The internal timer begins
counting after VCC 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.
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 VCC 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 signal, 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 worstcase specifications over their entire operating temperature range. Choose a reset threshold guaranteed to
assert at a voltage below the power supply’s regulation
range and above the minimum specified operating voltage range for the system’s ICs.
MAXIMUM TRANSIENT DURATION (µs)
300
TA = +25°C
250
MAX821/822 FIG-01
Reset Output
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 VCC > 1V. Once VCC 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.
MAX821/MAX822
_______________Detailed Description
200
150
100
50
0
1
10
100
1000
RESET COMPARATOR OVERDRIVE, VTH-VCC (mV)
Figure 1. Maximum Transient Duration Without Causing a
Reset Pulse vs. Comparator Overdrive
__________Applications Information
Negative-Going VCC Transients
While designed to issue a reset to the microprocessor
(µP) during power-up, power-down, and brownout conditions, the MAX821/MAX822 are relatively immune to
short-duration, negative-going VCC 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 VCC,
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 VCC transient may have
without causing a reset pulse to be issued. As the magnitude of the transient increases (goes farther below the
reset threshold), the maximum allowable pulse width
decreases. Typically, for the MAX821/MAX822, a VCC
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 VCC can provide additional transient immunity, if
desired.
_______________________________________________________________________________________
5
MAX821/MAX822
4-Pin µP Voltage Monitors with Pin-Selectable
Power-On Reset Timeout Delay
Ensuring a Valid RESET Output
Down to VCC = 0V
When VCC falls below 1V, the MAX821 RESET output
no longer sinks current—it becomes an open circuit.
Therefore, high-impedance CMOS logic inputs connected to the RESET output can drift to undetermined
voltages. This presents no problem in most applications, since most µP and other circuitry is inoperative
with VCC below 1V. However, in applications where the
RESET output must be valid down to 0V, adding a pulldown resistor to the RESET pin will cause any stray
leakage currents to flow to ground, holding RESET low
(Figure 2a). R1’s value is not critical; 100kΩ is large
enough not to load RESET, and small enough to pull
RESET to ground.
A 100kΩ pull-up resistor to VCC is also recommended
for the MAX822 if RESET is required to remain valid for
VCC < 1V (Figure 2b).
VCC
VCC
VCC
VCC
R1
MAX822
MAX821
RESET
RESET
R1
GND
GND
b)
a)
Figure 2. RESET/RESET Valid to VCC = Ground Circuit
Interfacing to µPs with
Bidirectional Reset Pins
µPs with bidirectional reset pins (such as the Motorola
68HC11 series) can contend with the MAX821 reset
output. For example, if the MAX821 RESET output is
asserted high and the µP wants to pull it low, indeterminate logic levels may result. To correct such cases,
connect a 4.7kΩ resistor between the MAX821 RESET
output and the µP reset I/O (Figure 3). Buffer the reset
output to other system components.
___________________Chip Information
BUFFER
VCC
VCC
MAX821
RESET
GND
BUFFERED RESET
TO OTHER SYSTEM
COMPONENTS
4.7k
µP
RESET
GND
TRANSISTOR COUNT: 492
Figure 3. Interfacing to µPs with Bidirectional Reset I/O
6
_______________________________________________________________________________________
4-Pin µP Voltage Monitors with Pin-Selectable
Power-On Reset Timeout Delay
SOT-143 4L.EPS
PACKAGE OUTLINE, SOT-143, 4L
21-0052
E
1
1
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.
7 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2005 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products, Inc.
MAX821/MAX822
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.)
Similar pages