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Low-Cost Microprocessor Supervisory
Circuits with Battery Backup
General Description
The MAX703/MAX704 microprocessor (µP) supervisory
circuits reduce the complexity and number of compo-
nents required for power-supply monitoring and battery
control functions in µP systems. These devices signifi-
cantly improve system reliability and accuracy com-
pared to that obtained with separate ICs or discrete
components.
The MAX703/MAX704 are available in 8-pin DIP and SO
packages and provide four functions:
1) An active-low reset during power-up, power-down,
and brownout conditions.
2) Battery-backup switching for CMOS RAM, CMOS
µPs, or other low-power logic circuitry.
3) A 1.25V threshold detector for power-fail warning,
low-battery detection, or for monitoring a power
supply other than +5V.
4) An active-low manual reset input.
The MAX703 and MAX704 differ only in their supply-
voltage monitor levels. The MAX703 generates a reset
when the supply drops below 4.65V, while the MAX704
generates a reset below 4.40V.
Features
♦
Battery-Backup Power Switching
♦
Precision Supply-Voltage Monitor
4.65V (MAX703)
4.40V (MAX704)
♦
200ms Reset Pulse Width
♦
Debounced TTL/CMOS-Compatible Manual Reset
Input
♦
200µA Quiescent Current
♦
50nA Quiescent Current in Battery-Backup Mode
♦
Voltage Monitor for Power-Fail or Low-Battery
Warning
♦
8-Pin DIP and SO Packages
♦
Guaranteed
RESET
Assertion to V
CC
= 1V
MAX703/MAX704
Ordering Information
PART
MAX703C/D
MAX703CPA
MAX703CSA
MAX703EPA
MAX703ESA
MAX703MJA
MAX704C/D
MAX704CPA
MAX704CSA
MAX704EPA
MAX704ESA
MAX704MJA
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
-55°C to +125°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
-55°C to +125°C
PIN-PACKAGE
Dice*
8 PDIP
8 SO
8 PDIP
8 SO
8 CERDIP**
Dice*
8 PDIP
8 SO
8 PDIP
8 SO
8 CERDIP**
Applications
Computers
Controllers
Intelligent Instruments
Automotive Systems
Critical µP Power Monitoring
Typical Operating Circuit
UNREGULATED DC
R1
REGULATED +5V
MICROPROCESSOR
V
CC
0.1µF
V
CC
PFI
3.6V
LITHIUM
BATTERY
V
BATT
MR
MAX703
MAX704
V
OUT
V
CC
CMOS RAM
PUSHBUTTON
SWITCH
GND
RESET
PFO
RESET
NMI
GND
*Dice
are tested at T
A
= +25°C only.
**Contact
factory for availability and processing to MIL-STD-883.
Devices in PDIP and SO packages 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. Lead free
not available for CERDIP package.
Pin Configuration
TOP VIEW
V
OUT
1
V
CC
GND
2
3
8
7
V
BATT
RESET
MR
PFO
R2
BUS
GND
MAX703
MAX704
6
5
PFI 4
DIP/SO
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
Low-Cost Microprocessor Supervisory
Circuits with Battery Backup
MAX703/MAX704
ABSOLUTE MAXIMUM RATINGS
Terminal Voltage (with respect to GND)
V
CC
....................................................................-0.3V to +6.0V
V
BATT
.................................................................-0.3V to +6.0V
All Other Inputs (Note 1).........................-0.3V to (V
CB
+ 0.3V)
Input Current
V
CC
...............................................................................200mA
V
BATT
..............................................................................50mA
GND ................................................................................20mA
Output Current
V
OUT
...............................Short-Circuit Protected for Up to 10s
All Other Outputs ............................................................20mA
Rate-of-Rise V
BATT
, V
CC
.................................................100V/µs
Operating Temperature Range
C Suffix................................................................0°C to +70°C
E Suffix .............................................................-40°C to +85°C
M Suffix ..........................................................-55°C to +125°C
Continuous Power Dissipation (T
A
= +70°C)
8-Pin PDIP (derated 9.09mW/°C above +70°C) ..........727mW
8-Pin SO (derated 5.88mW/°C above +70°C) .............471mW
8-Pin CERDIP (derated 8.00mW/°C above +85°C) .....640mW
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10s) .................................+300°C
Note 1:
V
CB
is the greater of V
CC
and V
BATT
. The input voltage limits on PFI and
MR
may be exceeded if the current into these pins
is limited to less than 10mA.
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
= +4.75V to +5.5V for MAX703, V
CC
= +4.5V to +5.5V for MAX704, V
BATT
= 2.8V, T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETER
Operating Voltage Range
V
CC
, V
BATT
Supply Current (Excluding
I
OUT
)
I
SUPPLY
in Battery-Backup
Mode (Excluding I
OUT
)
V
BATT
Standby Current
(Note 3)
I
SUPPLY
SYMBOL
(Note 2)
MAX70_C
MAX70_E/M
V
CC
= 0V, V
BATT
=
2.8V
5.5V > V
CC
> V
BATT
+ 0.2V
I
OUT
= 5mA
V
OUT
Output
I
OUT
= 50mA
V
OUT
in Battery-Backup
Mode
Battery Switch Threshold
(V
CC
- V
BATT
)
Battery Switchover Hysteresis
RESET
Threshold
RESET
Threshold Hysteresis
RESET
Pulse Width
t
RST
V
OH
RESET
Output Voltage
V
OL
I
SOURCE
= 800µA
I
SINK
= 3.2mA
MAX70_C, V
CC
= 1V, V
CC
falling,
V
BATT
= 0V, I
SINK
= 50µA
MAX70_E/M, V
CC
= 1.2V, V
CC
falling,
V
BATT
= 0V, I
SINK
= 100µA
140
V
CC
-
1.5
0.4
0.3
0.3
V
V
RST
MAX703
MAX704
4.50
4.25
I
OUT
= 250µA, V
CC
< V
BATT
- 0.2V
V
CC
< V
RST
Power-up
Power-down
T
A
= +25°C
T
A
= T
MIN
to T
MAX
T
A
= +25°C
T
A
= T
MIN
to T
MAX
-0.10
-1.00
V
CC
-
0.05
V
CC
-
0.5
V
BATT
-
0.1
V
CC
-
0.025
V
CC
-
0.25
V
BATT
-
0.02
20
-20
40
4.65
4.40
40
200
280
4.75
4.50
CONDITIONS
MIN
0
200
200
0.05
TYP
MAX
5.5
350
500
1.0
5.0
+0.02
+0.02
UNITS
V
µA
µA
µA
V
V
mV
mV
V
mV
ms
2
_______________________________________________________________________________________
Low-Cost Microprocessor Supervisory
Circuits with Battery Backup
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= +4.75V to +5.5V for MAX703, V
CC
= +4.5V to +5.5V for MAX704, V
BATT
= 2.8V, T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETER
MR
Input Threshold
MR
Pulse Width
MR
to
RESET
Delay
MR
Pullup Current
PFI Input Threshold
PFI Input Current
PFO
Output Voltage
V
OH
I
SOURCE
= 800µA
SYMBOL
V
IL
V
IH
t
MR
t
MD
MR
= 0V
V
CC
= 5V
100
1.20
-25
V
CC
-
1.5
0.4
250
1.25
+0.01
Low
High
2.0
150
250
600
1.30
+25
CONDITIONS
MIN
TYP
MAX
0.8
UNITS
V
ns
ns
µA
V
nA
V
MAX703/MAX704
I
SINK
= 3.2mA
V
OL
Note 2:
Either V
CC
or V
BATT
can go to 0V if the other is greater than 2.0V.
Note 3:
“-“ = battery-charging current, “+” = battery-discharging current.
Typical Operating Characteristics
(V
CC
= +5V, V
BATT
= 2.8V, T
A
= +25°C, unless otherwise noted.)
OUTPUT VOLTAGE vs. LOAD CURRENT
MAX703 toc01
OUTPUT VOLTAGE vs. LOAD CURRENT
V
CC
= 0V
V
BATT
= +2.8V
T
A
= +25°C
MAX703 toc02
MAX703 RESET OUTPUT VOLTAGE
vs. SUPPLY VOLTAGE
MAX703 toc03
5.00
V
CC
= +5V
V
BATT
= +2.8V
T
A
= +25°C
2.80
+5V
V
BATT
= 0V
T
A
= +25°C
V
CC
1V/div
4.95
2.78
V
OUT
(V)
V
OUT
(V)
4.90
SLOPE = 5Ω
4.85
2.76
OV
2.74
SLOPE = 80Ω
RESET
V
CC
V
CC
RESET
GND
2kΩ
RESET
330pF
+5V
1V/div
4.80
2.72
4.75
0
10
20
30
40
50
I
OUT
(mA)
2.70
0
0.2
0.4
0.6
0.8
1.0
I
OUT
(mA)
0V
500ms/div
MAX703 RESET RESPONSE TIME
MAX703 toc04
POWER-FAIL COMPARATOR
RESPONSE TIME
MAX703 toc05
POWER-FAIL COMPARATOR
RESPONSE TIME
MAX703 toc06
+5V
V
CC
+5V
+4V
+5V
PFI
+5V
PFO
V
CC
= +5V
T
A
= +25°C
+3V
PFO
PFI
PFO
1kΩ
+5V
PFO
1.25V
30pF
30pF
1kΩ
1V/div
T
A
= +25°C
0V
+1.30V
PFI
0V
2µs/div
400ns/div
1.25V
RESET
V
CC
V
CC
RESET
GND
10kΩ
RESET
30pF
0V
+1.30V
PFI
V
CC
= +5V
T
A
= +25°C
+1.20V +1.20V
400ns/div
_______________________________________________________________________________________
3
Low-Cost Microprocessor Supervisory
Circuits with Battery Backup
MAX703/MAX704
Pin Description
PIN
1
2
3
4
5
6
NAME
V
OUT
V
CC
GND
PFI
PFO
MR
FUNCTION
Supply Output for CMOS RAM. When V
CC
is above the reset threshold, V
OUT
connects to V
CC
through a p-
channel MOSFET switch. When V
CC
is below the reset threshold, the higher of V
CC
or V
BATT
is connected to V
OUT
.
+5V Supply Input
Ground
Power-Fail Comparator Input. When PFI is less than 1.25V,
PFO
goes low; otherwise
PFO
remains high. Connect
PFI to GND or V
CC
when not used.
Power-Fail Comparator Output. It goes low and sinks current when PFI is less than 1.25V; otherwise
PFO
remains high.
Manual Reset Input. Generates a reset pulse when pulled below 0.8V. This active-low input is TTL/CMOS
compatible and can be shorted to ground with a switch. It has an internal 250µA pullup current. Leave floating
when not used.
Reset Output. Remains low while V
CC
is below the reset threshold (4.65V for the MAX703, 4.40V for the MAX704).
It remains low for 200ms after V
CC
rises above the reset threshold (Figure 2) or
MR
goes from low to high.
7
RESET
8
Backup-Battery Input. When V
CC
falls below the reset threshold, V
BATT
is switched to V
OUT
if V
BATT
is 20mV
V
BATT
greater than V
CC
. When V
CC
rises 20mV above V
BATT
, V
CC
is switched to V
OUT
. The 40mV hysteresis prevents
repeated switching if V
CC
falls slowly.
+5V
V
CC
V
BATT
V
CC
+5V
V
OUT
RESET
GENERATOR
RESET
0V
+5V
1.25V
BATTERY-SWITCHOVER
CIRCUITRY
V
OUT
0V
V
RST
V
BATT
= 3.0V
3.0V
t
RST
RESET
0V
MR
PFI
PFO
+5V
PFO*
1.25V
GND
MAX703
MAX704
0V
*PFO DEPENDS ON PFI EXCEPT IN BATTERY-BACKUP MODE, WHERE PFO IS LOW.
Figure 1. Block Diagram
4
Figure 2. Timing Diagram
_______________________________________________________________________________________
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