MAX703/MAX704
Low-Cost Microprocessor Supervisory
Circuits with Battery Backup
General Description
The MAX703/MAX704 microprocessor (μP) supervisory
circuits reduce the complexity and number of components
required for power-supply monitoring and battery control
functions in μP systems. These devices significantly
improve system reliability and accuracy compared 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 supplyvolt-
age monitor levels. The MAX703 generates a reset when
the supply drops below 4.65V, while the MAX704 gener-
ates 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
Ordering Information
PART
MAX703C/D
MAX703CPA
MAX703CSA
MAX703EPA
MAX703ESA
MAX703MJA
MAX704C/D
MAX704CPA
MAX704CSA
MAX704EPA
MAX704ESA
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
PIN-PACKAGE
Dice*
8 PDIP
8 SO
8 PDIP
8 SO
8 CERDIP**
Dice*
8 PDIP
8 SO
8 PDIP
8 SO
Applications
●
●
●
●
Computers
Controllers
Intelligent Instruments
Critical μP Power Monitoring
Typical Operating Circuit
UNREGULATED DC
R1
REGULATED +5V
MICROPROCESSOR
V
CC
0.1µF
PFI
MAX703
MAX704
V
BATT
MR
GND
V
OUT
V
CC
CMOS RAM
GND
V
CC
RESET
PFO
RESET
NMI
BUS
GND
MAX704MJA
-55°C to +125°C
8 CERDIP**
*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(Pb)-free packaging. Specify lead(Pb)-free by adding
the “+” symbol at the end of the part number when ordering.
Lead(Pb)-free not available for CERDIP package.
R2
3.6V
LITHIUM
BATTERY
Pin Configuration
TOP VIEW
V
OUT
1
8
V
BATT
RESET
MR
PFO
V
CC
2
GND
3
MAX703
MAX704
7
6
5
PUSHBUTTON
SWITCH
PFI 4
DIP/SO
19-0130; Rev 3; 5/14
MAX703/MAX704
Absolute Maximum Ratings
Low-Cost Microprocessor Supervisory
Circuits with Battery Backup
Terminal Voltage (with respect to GND)
Rate-of-Rise V
BATT
, V
CC
................................................100V/μs
V
CC
...................................................................-0.3V to +6.0V
Operating Temperature Range
V
BATT
................................................................-0.3V to +6.0V
C Suffix................................................................0°C to +70°C
All Other Inputs (Note 1).......................-0.3V to (V
CB
+ 0.3V)
E Suffix.............................................................-40°C to +85°C
Input Current
M Suffix..........................................................-55°C to +125°C
V
CC
..............................................................................200mA
Continuous Power Dissipation (T
A
= +70°C)
V
BATT
............................................................................50mA
8-Pin PDIP (derated 9.09mW/°C above +70°C)..........727mW
GND................................................................................20mA
8-Pin SO (derated 5.88mW/°C above +70°C).............471mW
Output Current
8-Pin CERDIP (derated 8.00mW/°C above +85°C).....640mW
V
OUT
..............................Short-Circuit Protected for Up to 10s
Storage Temperature Range ............................-65°C to +160°C
All Other Outputs ............................................................20mA
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
)
VBATT Standby Current
(Note 3)
V
OUT
Output
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
I
OUT
= 50mA
I
OUT
= 250µA, V
CC
< V
BATT
- 0.2V
V
CC
< V
RST
Power-up
Power-down
4.50
4.25
140
I
SOURCE
= 800µA
I
SINK
= 3.2mA
V
OL
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
V
CC
-
1.5
0.4
0.3
0.3
V
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
-
V
CC
-
0.05
0.025
V
CC
-
V
CC
-
0.5
0.25
V
BATT
- V
BATT
-
0.1
0.02
20
-20
40
V
RST
MAX703
MAX704
4.65
4.40
40
t
RST
V
OH
RESET
Output Voltage
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
VOUT in Battery-Backup Mode
Battery Switch Threshold (V
CC
-
V
BATT
)
Battery Switchover Hysteresis
RESET
Threshold
RESET
Threshold Hysteresis
RESET
Pulse Width
V
mV
mV
V
mV
ms
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MAX703/MAX704
Electrical Characteristics (continued)
Low-Cost Microprocessor Supervisory
Circuits with Battery Backup
(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
V
OL
I
SOURCE
= 800µA
I
SINK
= 3.2mA
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
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
OUTPUT VOLTAGE vs. LOAD CURRENT
MAX703 toc01
(V
CC
= +5V, V
BATT
= 2.8V, T
A
= +25°C, unless otherwise noted.)
OUTPUT VOLTAGE vs. LOAD CURRENT
V
CC
= 0V
V
BATT
= +2.8V
T
A
= +25°C
MAX703 toc02
5.00
4.95
4.90
4.85
4.80
4.75
V
CC
= +5V
V
BATT
= +2.8V
T
A
= +25°C
2.80
2.78
2.76
2.74
2.72
2.70
MAX703
RESET
OUTPUT VOLTAGE
vs. SUPPLY VOLTAGE
V
BATT
= 0V
T
A
= +25°C
MAX703 toc03
+5V
V
CC
V
OUT
(V)
V
OUT
(V)
1V/div
SLOPE = 5Ω
SLOPE = 80Ω
OV
V
CC
RESET
V
CC
RESET
GND
2kΩ
RESET
330pF
+5V
1V/div
0
10
20
30
40
50
0
0.2
0.4
0.6
0.8
1.0
I
OUT
(mA)
I
OUT
(mA)
0V
500ms/div
MAX703
RESET
RESPONSE TIME
+5V
V
CC
MAX703 toc04
POWER-FAIL COMPARATOR
RESPONSE TIME
+4V
+5V
PFO
PFI
PFO
+5V
1kΩ
MAX703 toc05
POWER-FAIL COMPARATOR
RESPONSE TIME
PFI
+5V
PFO
MAX703 toc06
V
CC
= +5V
T
A
= +25°C
1kΩ
+5V
1V/div
10kΩ
RESET
30pF
PFO
1.25V
30pF
+3V
RESET
V
CC
V
CC
RESET
GND
T
A
= +25ºC
+1.30V
0V
PFI
1.25V
30pF
0V
0V
PFI
+1.30V
V
CC
= +5V
T
A
= +25°C
400ns/div
+1.20V
+1.20V
400ns/div
2µs/div
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Maxim Integrated │
3
MAX703/MAX704
Low-Cost Microprocessor Supervisory
Circuits with Battery Backup
Pin Description
PIN NAME
1
2
3
4
5
6
7
8
V
OUT
V
CC
GND
PFI
PFO
MR
RESET
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.
Backup-Battery Input. When V
CC
falls below the reset threshold, V
BATT
is switched to V
OUT
if V
BATT
is 20mV greater
V
BATT
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
BATTERY-SWITCHOVER
CIRCUITRY
V
OUT
0V
V
RST
V
BATT
= 3.0V
+5V
RESET
GENERATOR
V
OUT
3.0V
0V
+5V
1.25V
RESET
t
RST
RESET
0V
MR
PFI
PFO
+5V
PFO*
0V
1.25V
MAX703
MAX704
GND
*PFO DEPENDS ON PFI EXCEPT IN BATTERY-BACKUP MODE, WHERE
PFO
IS LOW.
Figure 1. Block Diagram
Figure 2. Timing Diagram
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MAX703/MAX704
Low-Cost Microprocessor Supervisory
Circuits with Battery Backup
MAX704 substrate, regardless of the voltage applied to
V
BATT
(Figure 3). During this time, diode D1 (between
V
BATT
and the substrate) conducts current from V
BATT
to
V
CC
if V
BATT
≥ (V
CC
+ 0.6V).
When the battery-backup mode is activated, V
BATT
con-
nects to V
OUT
. In this mode, the substrate connects to
V
BATT
and internal circuitry is powered from the battery
(Figure 3). Table 1 shows the status of the MAX703/
MAX704 inputs and outputs in battery-backup mode.
When V
CC
is below, but within, 1V of V
BATT
, the internal
switchover comparator draws about 30μA. Once V
CC
Detailed Description
RESET
Output
A μP’s reset input starts the μP in a known state.
Whenever the μP is in an unknown state, it should be held
in reset. The MAX703/MAX704 assert reset when V
CC
is
low, preventing code-execution errors during power-up,
power-down, or brownout conditions.
When V
BATT
is 2V or more,
RESET
is always valid,
irrespective of V
CC
. On power-up, as V
CC
rises,
RESET
remains low. When V
CC
exceeds the reset threshold, an
internal timer holds
RESET
low for a time equal to the
reset pulse width (typically 200ms); after this interval,
RESET
goes high (Figure 2). If a power-fail or brown-
out condition occurs (i.e., V
CC
drops below the reset
threshold),
RESET
is asserted. As long as V
CC
remains
below the reset threshold, the internal timer is continually
restarted, causing the
RESET
output to remain low. Thus,
a brownout condition that interrupts a previously initiated
reset pulse causes an additional 200ms delay from the
end of the last interruption.
Table 1. Input and Output Status in
Battery-Backup Mode
SIGNAL
VCC
VOUT
VBATT
RESET
PFI
PFO
MR
V
BATT
STATUS
Disconnected from VOUT.
Connected to VBATT through an internal 80Ω
p-channel MOSFET switch.
Connected to VOUT. Supply current is < 1µA
when VCC < (VBATT - 1V).
Logic-low.
Power-fail comparator is disabled.
Logic-low.
Disabled.
V
CC
Power-Fail Comparator
The PFI input is compared to an internal reference. If PFI
is less than 1.25V,
PFO
goes low. The power-fail com-
parator can be used as an undervoltage detector to signal
a failing power supply. In the
Typical Operating Circuit,
an external voltage-divider at PFI is used to monitor the
unregulated DC voltage from which the regulated +5V
supply is derived.
The voltage-divider can be chosen so the voltage at PFI falls
below 1.25V just before the +5V regulator drops out.
PFO
is
then used as an interrupt to prepare the μP for power-down.
To conserve power, the power-fail comparator is turned off
and
PFO
is forced low when the MAX703/MAX704 enter
battery-backup mode.
S1
S2
MAX703
MAX704
D1
D2
S3
S4
SUBSTRATE
D3
Backup-Battery Switchover
In the event of a brownout or power failure, it may be nec-
essary to preserve the contents of RAM. With a backup
battery installed at V
BATT
, the MAX703/MAX704 auto-
matically switch RAM to backup power when V
CC
fails.
As long as V
CC
exceeds the reset threshold, V
CC
con-
nects to V
OUT
through a 5Ω p-channel MOSFET power
switch. Once V
CC
falls below the reset threshold,
RESET
goes low and V
CC
or V
BATT
(whichever is higher) switch-
es to V
OUT
. Note that V
BATT
switches to V
OUT
through
an 80Ω switch only if V
CC
is below the resetthreshold volt-
age
and
V
BATT
is greater than V
CC
. When V
CC
exceeds
the reset threshold, it is connected to the MAX703/
V
OUT
CONDITION
V
CC
> Reset Threshold
V
CC
< Reset Threshold and
V
CC
> V
BATT
V
CC
< Reset Threshold and
V
CC
< V
BATT
S1/S2
Open
Open
Closed
S1/S2
Closed
Closed
Open
Figure 3. Battery-Switchover Block Diagram
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