19-0151; Rev 0; 6/93
µP Power-Supply Monitor
with Reset
_______________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 1/27
th
the power from a +5V supply.
The MAX7705 monitors the power supply in µP and digital
systems. The
RESET
output is valid for V
CC
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 V
CC
is below the
reset threshold,
RESET
is low and holds the µP in reset.
RESET
will go high 280ms after V
CC
rises above the
reset threshold. The MAX7705 is available in 8-pin DIP
and SO packages.
FEATURE
MAX7705
0
65µA
35µA
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
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
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
V
CC
N.C.
N.C.
RESET
MAX7705
N.C.
N.C.
N.C.
GND
V
CC
8
N.C. 7
N.C. 6
RESET 5
RESET
GND
µP
*
*
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.
µP Power-Supply Monitor
with Reset
MAX7705
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 Disipation (T
A
= +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
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
MAX7705C
V
CC
Range
MAX7705E
MAX7705C, V
CC
< 5.5V
Supply Current
MAX7705E, V
CC
< 5.5V
RESET
Threshold
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
= 3.2mA, V
CC
= reset threshold min
RESET
Output Voltage
I
SINK
= 50µA, V
CC
≥
1.0V, MAX7705C
I
SINK
= 100µA, V
CC
≥
1.2V, MAX7705E
I
SOURCE
= 800µA, V
CC
≥
reset threshold max
V
CC
- 1.5
140
4.50
65
4.65
20
280
560
0.4
0.3
V
0.4
200
4.75
V
µs
ms
1.2
65
5.5
150
µA
CONDITIONS
MIN
1.0
TYP
MAX
5.5
V
UNITS
2
_______________________________________________________________________________________
µP Power-Supply Monitor
with Reset
__________________________________________Typical Operating Characteristics
(T
A
= +25°C, 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)
V
CC
= RESET THRESHOLD MAX
V
CC
RISING
SUPPLY CURRENT (µA)
100
SUPPLY CURRENT
vs. TEMPERATURE
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)
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 (µs)
20
16
12
8
4
0
-60
-20
20
60
100
TEMPERATURE (°C)
V
CC
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
V
CC
FUNCTION
No Connection. There is no internal connection to these pins.
Ground
Reset Output remains low while V
CC
is below the reset threshold, and for 280ms after V
CC
rises above the
reset threshold.
+5V Supply Voltage
_______________________________________________________________________________________
3
µP Power-Supply Monitor
with Reset
MAX7705
MAXIMUM TRANSIENT DURATION (µs)
150
T
A
= +25°C
100
50
10ns
0
10
100
1k
10k
RESET COMPARATOR OVERDRIVE, V
TH
- V
CC
(mV)
mum pulse width 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, 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.
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 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 V
CC
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.
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: V
CC
, 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 V
CC
voltage and asserts
reset whenever V
CC
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).
V
CC
MAX7705
RESET
R1
GND
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 V
CC
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 V
CC
, 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 V
CC
= Ground Circuit
4
_______________________________________________________________________________________
µP Power-Supply Monitor
with Reset
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 4.7kΩ resistor between the MAX7705
RESET
output and the µP 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)
V
CC
V
CC
µP
RESET
MAX7705
RESET
4.7k
TRANSISTOR COUNT = 380;
SUBSTRATE CONNECTED TO V
CC
.
GND
GND
Figure 3. Interfacing to µPs with Bidirectional Reset I/O
_______________________________________________________________________________________
5
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