MAX709
Power-Supply Monitor with Reset
________________________________________________________________ Maxim Integrated Products
1
N.C.
N.C.
RESET
V
CC
N.C.
GND
N.C.
N.C.
1
2
3
4
8
7
6
5
DIP/SO/
MAX
MAX709
__________________Pin Configuration
TOP VIEW
RESET
GND
GND
V
CC
V
CC
P
MAX709
RESET
__________Typical Operating Circuit
Call toll free 1-800-998-8800 for free samples or literature.
19-0136; Rev. 1; 6/94
_______________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 P 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, MAX, and SO packages.
_______________________Applications
Minimum Component Count,
Low-Cost Processor Systems
___________________________Features
o
+5V, +3.3V, and +3V Versions
o
No External Components
o
Low Cost
o
Precise Power-Down Reset Threshold
o
140ms Min Power-On Reset Delay
o
Immune to Short Negative V
CC
Transients
o
8-Pin DIP, MAX, and SO Packages
o
Low Supply Current: 35A - MAX709R/S/T
65A - MAX709L/M
______________Ordering Information
PART
TEMP. RANGE
PIN-PACKAGE
MAX709_CPA
0C to +70C
MAX709_CSA
0C to +70C
8 SO
MAX709_C/D
0C to +70C
Dice
MAX709_EPA
-40C to +85C
8 Plastic DIP
MAX709_ESA
-40C to +85C
8 SO
8 Plastic DIP
* Dice are specified at T
A
= +25C, 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)
L
4.65
M
4.40
T
3.08
S
2.93
R
2.63
MAX709_CUA
0C to +70C
8 MAX
MAX709_EUA
-40C to +85C
8 MAX
MAX709
Power-Supply Monitor with Reset
2
_______________________________________________________________________________________
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/s
Continuous Power Dissipation (T
A
= +70C)
Plastic DIP (derate 9.09mW/C above +70C) . . . . . . . . 727mW
MAX (derate 4.10mW/C above +70C) . . . . . . . . . . . . . 330mW
SO (derate 5.88mW/C above +70C). . . . . . . . . . . . . . . . . 471mW
Operating Temperature Ranges
MAX709_C___ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0C to +70C
MAX709_E___ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -40C to +85C
Storage Temperature Range . . . . . . . . . . . . . . . . . . - 65C to +160C
Lead Temperature (soldering, 10sec). . . . . . . . . . . . . . . . . . . . +300C
ELECTRICAL CHARACTERISTICS
(V
CC
= full range, T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
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.
Note 1:
Supply current is measured with V
CC
= 3.6V for MAX709R/S/T, and V
CC
= 5.5V for all versions.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
CC
Range
1.0
5.5
V
1.2
5.5
Supply Current (Note 1)
35
85
A
35
110
All versions
65
150
65
200
RESET Threshold, V
TH
MAX709L
4.50
4.65
4.75
V
MAX709M
4.25
4.40
4.50
MAX709T
3.00
3.08
3.15
MAX709S
2.85
2.93
3.00
MAX709R
2.55
2.63
2.70
V
CC
to RESET Delay
V
CC
= reset threshold max to reset threshold min
20
s
Reset Active Timeout Period
V
CC
= reset threshold max, V
CC
rising
140
280
560
ms
RESET Output Voltage
0.3
V
0.4
I
SINK
= 50A, V
CC
1.0V, MAX709_C
0.3
I
SINK
= 100A, V
CC
1.2V, MAX709_E
0.4
I
SOURCE
= 800A, V
CC
reset threshold max,
MAX709L/M only
MAX709_C
MAX709_E
MAX709_C, V
CC
< 3.6V
MAX709_E, V
CC
< 3.6V
MAX709_C, V
CC
< 5.5V
MAX709_E, V
CC
< 5.5V
MAX709R/S/T only
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
I
SOURCE
= 500A, V
CC
reset threshold max,
MAX709R/S/T only
0.8 x V
CC
V
CC
- 1.5
ABSOLUTE MAXIMUM RATINGS
MAX709
Power-Supply Monitor with Reset
_________________________________________________________________________________________________
3
300
0
-60
100
POWER-UP RESET DELAY
vs. TEMPERATURE
50
250
TEMPERATURE (C)
POWER-UP RESET DELAY (ms)
60
150
100
-20
20
200
V
CC
= RESET THRESHOLD MAX,
V
CC
RISING
100
20
-60
-20
60
100
SUPPLY CURRENT
vs. TEMPERATURE
40
80
TEMPERATURE (C)
SUPPLY CURRENT (
A)
20
60
0
NOTE: STEADY-STATE SUPPLY
CURRENT IS INDEPENDENT
OF RESET OUTPUT STATUS
NO LOAD
V
CC
= +5V
V
CC
= +4V
V
CC
= +3V
V
CC
= +2V
V
CC
= +1V
24
0
-60
100
POWER-DOWN RESET DELAY
vs. TEMPERATURE
4
20
TEMPERATURE (C)
POWER-DOWN RESET DELAY (
s)
60
12
8
-20
20
16
V
CC
STEPPED FROM RESET THRESHOLD
MAX TO RESET THRESHOLD MIN
__________________________________________Typical Operating Characteristics
1.005
0.997
-60
-20
60
100
NORMALIZED RESET THRESHOLD
vs. TEMPERATURE
0.999
1.003
TEMPERATURE (C)
NORMALIZED RESET THRESHOLD
20
1.001
0.995
THE RESET THRESHOLD IS SHOWN
NORMALIZED TO 1, REPRESENTING
ALL AVAILABLE MAX709 RESET
THRESHOLDS
MAX709
Power-Supply Monitor with Reset
4
_______________________________________________________________________________________
__________Applications Information
Negative-Going V
CC
Transients
In addition to issuing a reset to the microprocessor
(P) 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 40s or less will not
cause a reset pulse to be issued.
A 0.1F 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 P 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 100k
, which is large enough
not to load RESET and small enough to pull RESET to
ground.
____________________Pin Description
PIN
NAME
FUNCTION
N.C.
No Connect. There is no internal
connection to this pin.
2
V
CC
+5V, +3.3V, or +3V Supply Voltage
3
GND
Ground
7
RESET
1, 4, 5,
6, 8
Reset Output remains low while V
CC
is
below the reset threshold, and for
280ms after V
CC
rises above the reset
threshold.
150
0
10
100
10k
50
100
RESET COMPARATOR OVERDRIVE, V
TH
- V
CC
(mV)
MAXIMUM TRANSIENT DURATION (
s)
1k
MAX709L/M
MAX709R/S/T
T
A
= +25C
10ns
Figure 1. Maximum Transient Duration without Causing a
Reset Pulse vs. Reset Comparator Overdrive
MAX709
Power-Supply Monitor with Reset
_______________________________________________________________________________________
5
Interfacing to Ps 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 P wants to pull
it low, indeterminate logic levels may result. To correct
this, connect a 4.7k
resistor between the MAX709
RESET output and the P reset I/O (see Figure 3).
Buffer the MAX709 RESET output to other system com-
ponents.
R1
V
CC
GND
MAX709
RESET
Figure 2. RESET Valid to V
CC
= Ground Circuit
4.7k
V
CC
GND
RESET
MAX709
V
CC
GND
P
BUFFER
BUFFERED RESET
TO OTHER SYSTEM
COMPONENTS
RESET
Figure 3. Interfacing to Ps with Bidirectional Reset I/O
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