ICL7673 Intersil Corporation, ICL7673 Datasheet - Page 5

• Manufacturer Part Number: ICL7673
• Description: Automatic Battery Back-Up Switch
• Manufacturer: Intersil Corporation

Applications for the ICL7673 include volatile semiconductor
memory storage systems, real-time clocks, timers, alarm
systems, and over/under the voltage detectors. Other
systems requiring DC power when the master AC line supply
fails can also use the ICL7673.
PRIMARY
FIGURE 8. APPLICATION REQUIRING RECHARGEABLE
SUPPLY
PRIMARY
BATTERY
SUPPLY
LITHIUM
FIGURE 7. ICL7673 BATTERY BACKUP CIRCUIT
+5V
RECHARGEABLE
GND
120/240
GND
VAC
+5V
POWER
BATTERY BACKUP
MAIN
BATTERY
+5V
R
C
+
-
2
8
FUSE
V
V
P
S
+
-
FIGURE 9. POWER SUPPLY FOR LOW POWER PORTABLE AC TO DC SYSTEMS
GND
2
DETECTOR
8
POWER
5
TRANSFORMER
4
FAIL
V
V
Pbar
P
S
STEPDOWN
V
FIGURE 10. TYPICAL MICROPROCESSOR MEMORY APPLICATION
O
GND
6
1
4
V
INTERRUPT SIGNAL
O
RECTIFIER
1
BRIDGE
V
+5V OR +3V
R
STATUS
INDICATOR
O
I
V
+5V OR +3V
O
C
1
MICROPROCESSOR
ICL7673
REGULATOR
8
ICL7663
4
A typical application, as illustrated in Figure 12, would be a
microprocessor system requiring a 5V supply. In the event of
primary supply failure, the system is powered down, and a
3V battery is employed to maintain clock or volatile memory
data. The main and backup supplies are connected to V
and V
clock or volatile memory. The ICL7673 will sense the main
supply, when energized, to be of greater potential than V
and connect, via its internal MOS switches, V
The backup input, V
event of main supply failure, the circuit will sense that the
backup supply is now the greater potential, disconnect V
from V
Figure 11 illustrates the use of external PNP power
transistors to increase the power switching capability of the
circuit. In this application the output current is limited by the
beta and thermal characteristics of the power transistors.
If hysteresis is desired for a particular low power application,
positive feedback can be applied between the input V
open drain output S
Figure 12. For high power applications hysteresis can be
applied as shown in Figure 13.
The ICL7673 can also be used as a clipping circuit as
illustrated in Figure 14. With high impedance loads the
circuit output will be nearly equal to the greater of the two
input signals.
VOLATILE
2
6
RAM
S
O
R
R
, with the circuit output V
, and connect V
2
1
V
O
R
3
D
BAR
S
1
BACKUP CIRCUIT
will be disconnected internally. In the
+
-
S
through a resistor as illustrated in
.
ICL7673
V
BATTERY
STACK
V
P
S
V
2
O
8
P
BATTERY
BACK-UP
ICL7673
supplying power to the
4
GND
1
V
S
P
to output V
+
-
V
July 22, 2005
O
P
FN3183.4
and
P
S
P
O
.