19-0136; Rev. 2; 12/05
Power-Supply Monitor with Reset
MAX709
_______________General Description
The MAX709 provides a system reset during power-up,
power-down, and brownout conditions. When V
CC
falls
below the reset threshold, RESET goes low and holds
the µP in reset for 140ms min after V
CC
rises above the
threshold.
The RESET output is guaranteed to be in the correct
state with V
CC
down to 1V. The MAX709 provides
excellent circuit reliability and low cost by eliminating
external components and adjustments when used with
+5V, +3.3V, or +3V powered systems. The MAX709 is
available 8-pin DIP, µMAX, and SO packages.
___________________________Features
♦
+5V, +3.3V, and +3V Versions
♦
No External Components
♦
Low Cost
♦
Precise Power-Down Reset Threshold
♦
140ms Min Power-On Reset Delay
♦
Immune to Short Negative V
CC
Transients
♦
8-Pin DIP, µMAX, and SO Packages
♦
Low Supply Current: 35µA - MAX709R/S/T
65µA - MAX709L/M
______________Ordering Information
PART
MAX709_CPA
MAX709_CUA
MAX709_CSA
MAX709_C/D
TEMP. RANGE
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
8 Plastic DIP
8 µMAX
8 SO
Dice
8 Plastic DIP
8 µMAX
8 SO
_______________________Applications
Minimum Component Count,
Low-Cost Processor Systems
MAX709_EPA
MAX709_EUA
MAX709_ESA
Devices are available in both leaded and lead-free packaging.
Specify lead free by adding the + symbol at the end of the part
number when ordering.
*Dice
are specified at T
A
= +25°C, DC parameters only.
Note:
This part offers a choice of five different reset threshold
voltages. Select the letter corresponding to the desired
nominal reset threshold voltage, and insert it into the
blank to complete the part number.
RESET THRESHOLD
SUFFIX
VOLTAGE (V)
4.65
4.40
3.08
2.93
2.63
__________Typical Operating Circuit
L
M
T
S
R
V
CC
V
CC
µP
RESET
__________________Pin Configuration
TOP VIEW
N.C.
V
CC
GND
MAX709
RESET
1
2
3
4
DIP/SO/µMAX
MAX709
8
7
6
5
N.C.
RESET
N.C.
N.C.
GND
GND
N.C.
________________________________________________________________ Maxim Integrated Products
1
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Power-Supply Monitor with Reset
MAX709
ABSOLUTE MAXIMUM RATINGS
Terminal Voltage (with respect to GND)
V
CC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 6.0V
RESET. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to (V
CC
+ 0.3V)
Input Current, V
CC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20mA
Output Current, RESET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20mA
Rate-of-Rise, V
CC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100V/µs
Continuous Power Dissipation (T
A
= +70°C)
Plastic DIP (derate 9.09mW/°C above +70°C) . . . . . . . . 727mW
µMAX (derate 4.10mW/°C above +70°C) . . . . . . . . . . . . . 330mW
SO (derate 5.88mW/°C above +70°C). . . . . . . . . . . . . . . . . 471mW
Operating Temperature Ranges
MAX709_C___ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0°C to +70°C
MAX709_E___ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -40°C to +85°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
= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETER
V
CC
Range
MAX709_C
MAX709_E
MAX709R/S/T only
Supply Current (Note 1)
All versions
MAX709L
MAX709M
RESET Threshold, V
TH
MAX709T
MAX709S
MAX709R
V
CC
to RESET Delay
Reset Active Timeout Period
V
CC
= reset threshold max to reset threshold min
V
CC
= reset threshold max, V
CC
rising
I
SINK
= 1.2mA, V
CC
= reset threshold min,
MAX709R/S/T only
I
SINK
= 3.2mA, V
CC
= reset threshold min,
MAX709L/M only
RESET Output Voltage
I
SINK
= 50µA, V
CC
≥
1.0V, MAX709_C
I
SINK
= 100µA, V
CC
≥
1.2V, MAX709_E
I
SOURCE
= 500µA, V
CC
≥
reset threshold max,
MAX709R/S/T only
I
SOURCE
= 800µA, V
CC
≥
reset threshold max,
MAX709L/M only
0.8 x V
CC
V
CC
- 1.5
140
MAX709_C, V
CC
< 3.6V
MAX709_E, V
CC
< 3.6V
MAX709_C, V
CC
< 5.5V
MAX709_E, V
CC
< 5.5V
4.50
4.25
3.00
2.85
2.55
CONDITIONS
MIN
1.0
1.2
35
35
65
65
4.65
4.40
3.08
2.93
2.63
20
280
560
0.3
0.4
0.3
0.4
V
TYP
MAX
5.5
5.5
85
110
150
200
4.75
4.50
3.15
3.00
2.70
µs
ms
V
µA
UNITS
V
Note 1:
Supply current is measured with V
CC
= 3.6V for MAX709R/S/T, and V
CC
= 5.5V for all versions.
2
_______________________________________________________________________________________
Power-Supply Monitor with Reset
MAX709
__________________________________________Typical Operating Characteristics
POWER-UP RESET DELAY
vs. TEMPERATURE
300
250
200
150
100
50
0
-60
-20
20
60
100
TEMPERATURE (°C)
POWER-DOWN RESET DELAY (µs)
POWER-UP RESET DELAY (ms)
V
CC
= RESET THRESHOLD MAX,
V
CC
RISING
24
20
16
12
8
4
0
-60
POWER-DOWN RESET DELAY
vs. TEMPERATURE
V
CC
STEPPED FROM RESET THRESHOLD
MAX TO RESET THRESHOLD MIN
-20
20
60
100
TEMPERATURE (°C)
SUPPLY CURRENT
vs. TEMPERATURE
100
NORMALIZED RESET THRESHOLD
NOTE:
STEADY-STATE SUPPLY
CURRENT IS INDEPENDENT
OF RESET OUTPUT STATUS
NO LOAD
60
V
CC
= +5V
V
CC
= +4V
40
V
CC
= +3V
20
0
V
CC
= +2V
V
CC
= +1V
-60
-20
20
60
100
TEMPERATURE (°C)
1.005
NORMALIZED RESET THRESHOLD
vs. TEMPERATURE
THE RESET THRESHOLD IS SHOWN
NORMALIZED TO 1, REPRESENTING
ALL AVAILABLE MAX709 RESET
THRESHOLDS
SUPPLY CURRENT (µA)
80
1.003
1.001
0.999
0.997
0.995
-60
-20
20
60
100
TEMPERATURE (°C)
_________________________________________________________________________________________________
3
Power-Supply Monitor with Reset
MAX709
MAXIMUM TRANSIENT DURATION (µs)
____________________Pin Description
PIN
1, 4, 5,
6, 8
2
3
NAME
N.C.
V
CC
GND
FUNCTION
No Connect. There is no internal
connection to this pin.
+5V, +3.3V, or +3V Supply Voltage
Ground
Reset Output remains low while V
CC
is
below the reset threshold, and for
280ms after V
CC
rises above the reset
threshold.
150
T
A
= +25°C
100
MAX709L/M
50
10ns
MAX709R/S/T
0
10
100
1k
10k
RESET COMPARATOR OVERDRIVE, V
TH
- V
CC
(mV)
7
RESET
__________Applications Information
Negative-Going V
CC
Transients
In addition to issuing a reset to the microprocessor
(µP) during power-up, power-down, and brownout con-
ditions, the MAX709 is relatively immune to short dura-
tion negative-going V
CC
transients (glitches).
Figure 1 shows typical transient duration vs. reset com-
parator overdrive, for which the MAX709 does not gen-
erate a reset pulse. The graph was generated using a
negative-going pulse applied to V
CC
, starting 1.5V
above the actual reset threshold and ending below it
by the magnitude indicated (reset comparator over-
drive). The graph indicates the typical maximum pulse
width that a negative-going V
CC
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
MAX709L/MAX709M, a V
CC
transient that goes 100mV
below the reset threshold and lasts 40µs or less will not
cause a reset pulse to be issued.
Figure 1. Maximum Transient Duration without Causing a
Reset Pulse vs. Reset Comparator Overdrive
A 0.1µF bypass capacitor mounted as close as possible
to pin 2 (V
CC
) provides additional transient immunity.
Ensuring a Valid RESET Output
Down to V
CC
= 0V
When V
CC
falls below 1V, the MAX709 RESET output
no longer sinks current—it becomes an open circuit.
Therefore, high-impedance CMOS logic inputs con-
nected to the RESET output can drift to undermined
voltages. This presents no problem in most applica-
tions, since most µP and other circuitry is inoperative
with V
CC
below 1V. However, in applications where the
RESET output must be valid down to 0V, adding a pull-
down resistor to the RESET pin will cause any stray
leakage currents to flow to ground, holding RESET low
(see Figure 2). The resistance value of R1 is not criti-
cal. It should be about 100kΩ, which is large enough
not to load RESET and small enough to pull RESET to
ground.
4
_______________________________________________________________________________________
Power-Supply Monitor with Reset
MAX709
BUFFER
V
CC
V
CC
V
CC
µP
RESET
BUFFERED RESET
TO OTHER SYSTEM
COMPONENTS
MAX709
RESET
R1
GND
GND
GND
MAX709
RESET
4.7k
Figure 2.
RESET Valid to V
CC
= Ground Circuit
Figure 3. Interfacing to µPs with Bidirectional Reset I/O
Interfacing to µPs with
Bidirectional Reset Pins
Microprocessors with bidirectional reset pins (such as
the Motorola 68HC11 series) can contend with the
MAX709 reset output. If, for example the MAX709
RESET output is asserted high and the µP wants to pull
it low, indeterminate logic levels may result. To correct
this, connect a 4.7kΩ resistor between the MAX709
RESET output and the µP reset I/O (see Figure 3).
Buffer the MAX709 RESET output to other system com-
ponents.
_______________________________________________________________________________________
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