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19-0151; Rev 0; 6/93
P Power-Supply Monitor with Reset
_______________General Description
In applications with microprocessors (Ps) 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 P 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, powerdown, and brownout conditions. When VCC is below the reset threshold, RESET is low and holds the P 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.
FEATURE MAX7705 0 65A 35A Yes Yes TL7705 3 1.8mA 1.8mA No No
____________________________Features
o No External Components o Low Cost o Precise Reset Threshold o 280ms Power-On Reset Delay o 8-Pin DIP and SO Packages
MAX7705
______________Ordering Information
PART MAX7705CPA MAX7705CSA MAX7705C/D MAX7705EPA MAX7705ESA TEMP. RANGE 0C to +70C 0C to +70C 0C to +70C -40C to +85C -40C to +85C PIN-PACKAGE 8 Plastic DIP 8 SO Dice* 8 Plastic DIP 8 SO
No. of External Components Required Operating Supply Current Power-Supply Glitch Immunity Guaranteed Minimum Reset Delay
+5V +3V
* Contact factory for dice specifications.
________________________Applications
Minimum Component Count, Low-Cost Processor Systems
__________Typical Operating Circuit
__________________Pin Configuration
VCC
TOP VIEW *
1 2 3 N.C. 1 N.C. 2 N.C. 3 GND 4 8 7 VCC N.C. N.C. RESET
MAX7705
N.C. N.C. N.C. GND VCC 8 N.C. 7 N.C. 6 RESET 5 RESET GND
P
*
*
4
MAX7705
6 5
DIP/SO
* THE MAX7705 ELIMINATES THREE EXTERNAL COMPONENTS REQUIRED BY THE TL7705.
________________________________________________________________ Maxim Integrated Products
1
Call toll free 1-800-998-8800 for free samples or literature.
P Power-Supply Monitor with Reset MAX7705
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/s Continuous Power Disipation (TA = +70C) Plastic DIP (derate 9.09mW/C above +70C) ............727mW SO (derate 5.88mW/C above +70C) .........................471mW Operating Temperature Ranges: MAX7705C_ _ .....................................................0C to +70C MAX7705E_ _ ..................................................-40C to +85C Storage Temperature Range .............................-65C to +160C Lead Temperature (soldering, 10sec) .............................+300C
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 = TMIN to TMAX, unless otherwise noted.) PARAMETER MAX7705C VCC Range MAX7705E MAX7705C, VCC < 5.5V Supply Current MAX7705E, VCC < 5.5V RESET Threshold VCC to RESET Delay Reset Active Timeout Period VCC = reset threshold max to reset threshold min VCC = reset threshold max, VCC rising ISINK = 3.2mA, VCC = reset threshold min RESET Output Voltage ISINK = 50A, VCC 1.0V, MAX7705C ISINK = 100A, VCC 1.2V, MAX7705E ISOURCE = 800A, VCC reset threshold max VCC - 1.5 140 4.50 65 4.65 20 280 560 0.4 0.3 V 0.4 200 4.75 V s ms 1.2 65 5.5 150 A CONDITIONS MIN 1.0 TYP MAX 5.5 V UNITS
2
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P Power-Supply Monitor with Reset
__________________________________________Typical Operating Characteristics
(TA = +25C, unless otherwise noted.)
MAX7705
POWER-UP RESET DELAY vs. TEMPERATURE
300 POWER-UP RESET DELAY (ms) 250 200 150 100 50 0 -60 -20 20 60 100 TEMPERATURE (C) VCC = RESET THRESHOLD MAX VCC RISING SUPPLY CURRENT (A) 100
SUPPLY CURRENT vs. TEMPERATURE
NOTE: STEADY-STATE SUPPLY CURRENT IS INDEPENDENT OF RESET OUTPUT STATUS NO LOAD 60 VCC = +5V VCC = +4V 40 VCC = +3V 20 0 VCC = +2V VCC = +1V -60 -20 20 60 100 TEMPERATURE (C) RESET THRESHOLD (V) 4.665 4.660 4.655 4.650 4.645 4.640 4.635 4.630 -60
RESET THRESHOLD vs. TEMPERATURE
80
-20
20
60
100
TEMPERATURE (C)
POWER-DOWN RESET DELAY vs. TEMPERATURE
24 POWER-DOWN RESET DELAY (s) 20 16 12 8 4 0 -60 -20 20 60 100 TEMPERATURE (C)
VCC STEPPED FROM RESET THRESHOLD MAX TO RESET THRESHOLD MIN
______________________________________________________________Pin Description
PIN 1,2,3,6,7 4 5 8 NAME N.C. GND RESET VCC FUNCTION No Connection. There is no internal connection to these pins. Ground Reset Output remains low while VCC is below the reset threshold, and for 280ms after VCC rises above the reset threshold. +5V Supply Voltage
_______________________________________________________________________________________
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P Power-Supply Monitor with Reset MAX7705
MAXIMUM TRANSIENT DURATION (s) 150 TA = +25C
100
50 10ns 0 10 100 1k 10k RESET COMPARATOR OVERDRIVE, VTH - VCC (mV)
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 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 (VCC) provides additional transient immunity.
Ensuring a Valid RESET Output Down to VCC = 0V
When VCC falls below 1V, the MAX7705 RESET output no longer sinks current; it becomes high impedance. Therefore, high-impedance CMOS logic inputs connected to the RESET output can drift to indeterminate voltages. In most applications this presents no problem, as P 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 100k, which is large enough not to load RESET and small enough to pull RESET to ground.
Figure 1. Maximum Transient Duration without Causing a Reset Pulse vs. Reset Comparator Overdrive
__________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 P 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 guaranteed over the full temperature range. The RESET output both sources and sinks current (see RESET Output Voltage in the Electrical Characteristics).
VCC
MAX7705
RESET R1 GND
Negative-Going VCC 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 comparator overdrive for which the MAX7705 does not generate 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-
Figure 2. RESET Valid to VCC = Ground Circuit
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_______________________________________________________________________________________
P Power-Supply Monitor with Reset
Interfacing to Ps with Bidirectional Reset Inputs
Ps 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 P wants to pull it low, an indeterminate logic level may result. To correct this, connect a 4.7k resistor between the MAX7705 RESET output and the P reset I/O, as in Figure 3. Buffer the RESET signal to other system components.
___________________Chip Topography
MAX7705
V CC RESET 0.045" (1.143mm)
BUFFER
BUFFERED RESET TO OTHER SYSTEM COMPONENTS
GND 0.056" (1.422mm)
VCC
VCC P RESET
MAX7705
RESET
4.7k
TRANSISTOR COUNT = 380; SUBSTRATE CONNECTED TO VCC.
GND
GND
Figure 3. Interfacing to Ps with Bidirectional Reset I/O
_______________________________________________________________________________________
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P Power-Supply Monitor with Reset MAX7705
_______________________________________________________Package Information
D1
DIM A A1 A2 A3 B B1 C D D1 E E1 e eA eB L INCHES MAX MIN 0.200 - - 0.015 0.175 0.125 0.080 0.055 0.022 0.016 0.065 0.050 0.012 0.008 0.390 0.348 0.035 0.005 0.325 0.300 0.280 0.240 0.100 BSC 0.300 BSC 0.400 - 0.150 0.115 15 0 MILLIMETERS MIN MAX - 5.08 0.38 - 3.18 4.45 1.40 2.03 0.41 0.56 1.27 1.65 0.20 0.30 8.84 9.91 0.13 0.89 7.62 8.26 6.10 7.11 2.54 BSC 7.62 BSC - 10.16 2.92 3.81 0 15
21-324A
E D A3 A A2 E1
L
A1 e B
C B1 eA eB
8-PIN PLASTIC DUAL-IN-LINE PACKAGE
6
_______________________________________________________________________________________
P Power-Supply Monitor with Reset MAX7705
__________________________________________ Package Information (continued)
DIM A A1 B C D E e H h L INCHES MAX MIN 0.069 0.053 0.010 0.004 0.019 0.014 0.010 0.007 0.197 0.189 0.157 0.150 0.050 BSC 0.244 0.228 0.020 0.010 0.050 0.016 8 0 MILLIMETERS MIN MAX 1.35 1.75 0.10 0.25 0.35 0.49 0.19 0.25 4.80 5.00 3.80 4.00 1.27 BSC 5.80 6.20 0.25 0.50 0.40 1.27 0 8
21-325A
E
H
D A e B
0.127mm 0.004in.
h x 45
A1
C
L
8-PIN PLASTIC SMALL-OUTLINE PACKAGE
_______________________________________________________________________________________
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P Power-Supply Monitor with Reset MAX7705
P Supervisory Circuits
Part Number
MAX690A/692A MAX691A/693A MAX696 MAX697 MAX700 MAX703/704 MAX705/706 MAX706P MAX706R/S/T MAX707/708 MAX708R/S/T MAX709L/M/ R/S/T MAX791 MAX792L/M/ R/S/T MAX800L/M MAX802L/M MAX805L MAX813L MAX820L/M/ R/S/T MAX1232 MAX1259
Minimum Nominal Reset Reset Pulse Threshold Width (V) (ms)
4.65/4.40 4.65/4.40 Adj. Adj. 4.65/adj. 4.65/4.40 4.65/4.40 2.63 2.63/2.93/ 3.08 4.65/4.40 2.63/2.93/ 3.08 140 140/adj. 35/adj. 35/adj. 200 140 140 140 140 140 140
Nominal Watchdog Timeout Backup- CE Period Battery Write (sec) Switch Protect
1.6 1.6/adj. 1.6/adj. 1.6/adj. 1.6 1.6 1.6 1 1 1.6/adj. 1.6 1.6 1.6 1 0.15/0.60/1.2 /10ns /10ns /10ns /10ns /10ns
PowerFail Comparator
Manual- Watch- LowReset dog Line Input Output Output
Active- BatteryHigh On Reset Output
4.65/4.40/ 140 2.63/2.93/3.08 4.65 140 4.65/4.40/ 140 2.63/2.93/3.08 4.60/4.40 4.60/4.40 4.65 4.65 140 140 140 140
/2% /2%
4.65/4.40/ 140 2.63/2.93/3.08 4.37/4.62 250 -
/2%
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 (c) 1993 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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