_______________General Description
In applications with microprocessors (µPs) that have a
RESET input, the MAX7705 is functionally and socket
compatible with the TL7705, but requires no external
components. It provides power-supply glitch immunity
and a guaranteed power-up reset delay, while typically
consuming 1/27th the power from a +5V supply.
The MAX7705 monitors the power supply in µP and digital
systems. The RESET output is valid for VCC down to 1V.
The device offers excellent circuit reliability and low cost
by eliminating external components and adjustments.
A system reset is provided during power-up, power-
down, and brownout conditions. When VCC is below the
reset threshold, RESET is low and holds the µP in reset.
RESET will go high 280ms after VCC rises above the
reset threshold. The MAX7705 is available in 8-pin DIP
and SO packages.
________________________Applications
Minimum Component Count, Low-Cost
Processor Systems
____________________________Features
♦No External Components
♦Low Cost
♦Precise Reset Threshold
♦280ms Power-On Reset Delay
♦8-Pin DIP and SO Packages
______________Ordering Information
* Contact factory for dice specifications.
MAX7705
µP Power-Supply Monitor
with Reset
________________________________________________________________
Maxim Integrated Products
1
1
2
3
4
8
7
6
5
VCC
N.C.
N.C.
RESET
GND
N.C.
N.C.
N.C.
MAX7705
VCC
RESETGND
µP
*
*
*
* THE MAX7705 ELIMINATES THREE EXTERNAL 
COMPONENTS REQUIRED BY THE TL7705.
__________________Pin Configuration
1
2
3
4
8
7
6
5
VCC
N.C.
N.C.
RESET
GND
N.C.
N.C.
N.C.
MAX7705
DIP/SO
TOP VIEW
__________Typical Operating Circuit
Call toll free 1-800-998-8800 for free samples or literature.
19-0151; Rev 0; 6/93
PART TEMP. RANGE PIN-PACKAGE
MAX7705CPA 0°C to +70°C 8 Plastic DIP
MAX7705CSA 0°C to +70°C 8 SO
MAX7705C/D 0°C to +70°C Dice*
FEATURE MAX7705 TL7705
No. of External
Components Required 03
Operating Supply
Current 65µA 1.8mA
Power-Supply Glitch
Immunity Yes No
Guaranteed Minimum
Reset Delay Yes No
+5V
+3V 35µA 1.8mA MAX7705EPA -40°C to +85°C 8 Plastic DIP
MAX7705ESA -40°C to +85°C 8 SO
MAX7705
µP Power-Supply Monitor
with Reset
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
Terminal Voltage (with respect to GND)
VCC ......................................................................-0.3V to 6.0V
RESET....................................................-0.3V to (VCC + 0.3V)
Input Current, VCC ..............................................................20mA
Output Current, RESET ......................................................20mA
Rate-of-Rise, VCC............................................................100V/µs
Continuous Power Disipation (TA= +70°C)
Plastic DIP (derate 9.09mW/°C above +70°C) ............727mW
SO (derate 5.88mW/°C above +70°C).........................471mW
Operating Temperature Ranges:
MAX7705C_ _ .....................................................0°C to +70°C
MAX7705E_ _ ..................................................-40°C to +85°C
Storage Temperature Range.............................-65°C to +160°C
Lead Temperature (soldering, 10sec).............................+300°C
ELECTRICAL CHARACTERISTICS
(VCC = full range, TA= TMIN to TMAX, 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.
PARAMETER CONDITIONS MIN TYP MAX UNITS
MAX7705C 1.0 5.5
VCC Range MAX7705E 1.2 5.5 V
MAX7705C, VCC < 5.5V 65 150
Supply Current MAX7705E, VCC < 5.5V 65 200 µA
RESET Threshold 4.50 4.65 4.75 V
VCC to RESET Delay VCC = reset threshold max to reset threshold min 20 µs
Reset Active Timeout Period VCC = reset threshold max, VCC rising 140 280 560 ms
ISINK = 3.2mA, VCC = reset threshold min 0.4
V
ISINK = 50µA, VCC ≥1.0V, MAX7705C 0.3
RESET Output Voltage
ISOURCE = 800µA, VCC ≥reset threshold max VCC - 1.5
ISINK = 100µA, VCC ≥1.2V, MAX7705E 0.4
MAX7705
µP Power-Supply Monitor
with Reset
_______________________________________________________________________________________
3
24
0-60 100
POWER-DOWN RESET DELAY
vs. TEMPERATURE
4
20
TEMPERATURE (°C)
POWER-DOWN RESET DELAY (µs)
60
12
8
-20 20
16
VCC STEPPED FROM RESET THRESHOLD
MAX TO RESET THRESHOLD MIN
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
VCC = RESET THRESHOLD MAX 
VCC RISING
100
20
-60 -20 60 100
SUPPLY CURRENT
vs. TEMPERATURE
40
80
TEMPERATURE (°C)
SUPPLY CURRENT (µA)
20
60
0
NOTE: STEADY-STATE SUPPLY 
CURRENT IS INDEPENDENT 
OF RESET OUTPUT STATUS NO LOAD
VCC = +5V
VCC = +4V
VCC = +3V
VCC = +2V
VCC = +1V
4.640
-60 -20 60 100
RESET THRESHOLD
vs. TEMPERATURE
4.650
TEMPERATURE (°C)
RESET THRESHOLD (V)
20
4.660
4.630
4.655
4.645
4.665
4.635
__________________________________________Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
______________________________________________________________Pin Description
PIN NAME FUNCTION
1,2,3,6,7 N.C. No Connection. There is no internal connection to these pins.
4 GND Ground
5RESET Reset Output remains low while VCC is below the reset threshold, and for 280ms after VCC rises above the
reset threshold.
8 VCC +5V Supply Voltage
MAX7705
µP Power-Supply Monitor
with Reset
4 _______________________________________________________________________________________
__________Applications Information
Replacing the TL7705 with a MAX7705
in an Existing Design
The MAX7705 has only three active pins: VCC, GND,
and RESET. When using a TL7705 with a µP that has
a RESET input, simply plug the MAX7705 into the
same socket and omit the RESET pull-up resistor, reset
timing capacitor, and reference bypass capacitor (see
the
Typical Operating Circuit
).
The MAX7705 monitors the VCC voltage and asserts
reset whenever VCC falls below the reset threshold.
The reset power-up delay is created by an internal
fixed oscillator. This delay is 100% tested and guaran-
teed over the full temperature range. The RESET out-
put both sources and sinks current (see RESET Output
Voltage in the
Electrical Characteristics
).
Negative-Going V
CC
Transients
The MAX7705 asserts RESET during power-up,
power-down, and brownout conditions. However, it is
relatively immune to short-duration negative-going VCC
transients (glitches).
Figure 1 shows typical transient duration vs. reset com-
parator overdrive for which the MAX7705 does not gen-
erate a reset pulse. The graph was generated using a
fast-edge, negative-going pulse applied to VCC, starting
1.5V above the actual reset threshold and ending below
the reset threshold by the magnitude indicated (reset
comparator overdrive). It indicates the typical maxi-
mum 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, a VCC transient that
goes 100mV below the reset threshold and lasts 40µs
or less will not cause a reset pulse to be issued.
A 0.1µF bypass capacitor mounted as close as possible
to pin 2 (VCC) provides additional transient immunity.
Ensuring a Valid
RESET
Output
Down to V
CC
= 0V
When VCC falls below 1V, the MAX7705 RESET output
no longer sinks current; it becomes high impedance.
Therefore, high-impedance CMOS logic inputs con-
nected to the RESET output can drift to indeterminate
voltages. In most applications this presents no prob-
lem, as µP and other circuitry is generally inoperative
with VCC below 1V. In applications where the RESET
output must be valid down to 0V, adding a pull-down
resistor to the RESET pin (as shown in Figure 2) will
cause any stray leakage currents to flow to ground,
holding RESET low. The resistance value of R1 is not
critical. It should be about 100kΩ, which is large
enough not to load RESET and small enough to pull
RESET to ground.
150
010 100 10k
50
100
RESET COMPARATOR OVERDRIVE, VTH - VCC (mV)
MAXIMUM TRANSIENT DURATION (µs)
1k
TA = +25°C
10ns
R1
VCC
GND
MAX7705
RESET
Figure 1. Maximum Transient Duration without Causing a
Reset Pulse vs. Reset Comparator Overdrive
Figure 2.
RESET
Valid to V
CC
= Ground Circuit
___________________Chip Topography
TRANSISTOR COUNT = 380;
SUBSTRATE CONNECTED TO VCC.
MAX7705
µP Power-Supply Monitor
with Reset
_______________________________________________________________________________________ 5
4.7k
VCC
GND
RESET
MAX7705
RESET
VCC
GND
µP
BUFFER BUFFERED RESET
TO OTHER SYSTEM
COMPONENTS
Figure 3. Interfacing to µPs with Bidirectional Reset I/O
Interfacing to µPs with
Bidirectional Reset Inputs
µPs with bidirectional reset pins, such as Motorola’s
68HC11 series, can contend with the MAX7705 reset
output. If, for example, the MAX7705 RESET output is
asserted high and the µP wants to pull it low, an inde-
terminate logic level may result. To correct this, con-
nect a 4.7kΩresistor between the MAX7705 RESET
output and the µP reset I/O, as in Figure 3. Buffer the
RESET signal to other system components.
RESET
VCC
GND
0.045"
(1.143mm)
0.056"
(1.422mm)
MAX7705
µP Power-Supply Monitor
with Reset
6 _______________________________________________________________________________________
C
AA2
E1
D
E
eA
eB
A3
B1
B
DIM
A
A1
A2
A3
B
B1
C
D
D1
E
E1
e
eA
eB
L
α
MIN
–
0.015
0.125
0.055
0.016
0.050
0.008
0.348
0.005
0.300
0.240
–
0.115
0˚
MAX
0.200
–
0.175
0.080
0.022
0.065
0.012
0.390
0.035
0.325
0.280
0.400
0.150
15˚
MIN
–
0.38
3.18
1.40
0.41
1.27
0.20
8.84
0.13
7.62
6.10
–
2.92
0˚
MAX
5.08
–
4.45
2.03
0.56
1.65
0.30
9.91
0.89
8.26
7.11
10.16
3.81
15˚
INCHES MILLIMETERS
2.54 BSC
7.62 BSC
0.100 BSC
0.300 BSC
A1
L
D1
e
21-324A
α8-PIN PLASTIC
DUAL-IN-LINE
PACKAGE
_______________________________________________________Package Information
MAX7705
µP Power-Supply Monitor
with Reset
_______________________________________________________________________________________ 7
L
DIM
A
A1
B
C
D
E
e
H
h
L
α
MIN
0.053
0.004
0.014
0.007
0.189
0.150
0.228
0.010
0.016
0˚
MAX
0.069
0.010
0.019
0.010
0.197
0.157
0.244
0.020
0.050
8˚
MIN
1.35
0.10
0.35
0.19
4.80
3.80
5.80
0.25
0.40
0˚
MAX
1.75
0.25
0.49
0.25
5.00
4.00
6.20
0.50
1.27
8˚
INCHES MILLIMETERS
α
8-PIN PLASTIC
SMALL-OUTLINE
PACKAGE
HE
D
e
A
A1 C
h x 45˚
0.127mm
0.004in.
B
1.27 BSC0.050 BSC
21-325A
__________________________________________ Package Information (continued)
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.
8
___________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600
© 1993 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
MAX7705
µP Power-Supply Monitor
with Reset
Minimum Nominal
Nominal Reset Watchdog Power-
Reset Pulse Timeout Backup-
CE
- Fail Manual- Watch- Low- Active- Battery-
Part Threshold Width Period Battery Write Com- Reset dog Line High On
Number (V) (ms) (sec) Switch Protect parator Input Output Output Reset Output
MAX690A/692A 4.65/4.40 140 1.6 ✔✔
MAX691A/693A 4.65/4.40 140/adj. 1.6/adj. ✔✔/10ns ✔✔✔✔✔
MAX696 Adj. 35/adj. 1.6/adj. ✔ ✔ ✔✔ ✔✔
MAX697 Adj. 35/adj. 1.6/adj. ✔✔ ✔✔ ✔
MAX700 4.65/adj. 200 - ✔✔
MAX703/704 4.65/4.40 140 - ✔✔✔
MAX705/706 4.65/4.40 140 1.6 ✔✔✔
MAX706P 2.63 140 1.6 ✔✔✔ ✔
MAX706R/S/T 2.63/2.93/ 140 1.6 ✔✔✔
3.08
MAX707/708 4.65/4.40 140 - ✔✔ ✔
MAX708R/S/T 2.63/2.93/ 140 - ✔✔ ✔
3.08
MAX709L/M/ 4.65/4.40/ 140 -
R/S/T 2.63/2.93/3.08
MAX791 4.65 140 1 ✔✔/10ns ✔ ✔✔✔ ✔✔
MAX792L/M/ 4.65/4.40/ 140 1 ✔/10ns ✔ ✔✔✔ ✔
R/S/T 2.63/2.93/3.08
MAX800L/M 4.60/4.40 140 1.6/adj. ✔✔/10ns ✔/±2% ✔✔ ✔✔
MAX802L/M 4.60/4.40 140 1.6 ✔✔/±2%
MAX805L 4.65 140 1.6 ✔✔ ✔
MAX813L 4.65 140 1.6 ✔✔✔ ✔
MAX820L/M/ 4.65/4.40/ 140 1 ✔/10ns ✔/±2% ✔✔✔ ✔
R/S/T 2.63/2.93/3.08
MAX1232 4.37/4.62 250 0.15/0.60/1.2 ✔
MAX1259 - - - ✔✔
µ
P Supervisory Circuits