ICL7673CPA(1999) Ver la hoja de datos (PDF) - Intersil
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ICL7673CPA Datasheet PDF : 7 Pages
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ICL7673
supply voltage. A low-impedance capacitor such as a
0.047µF disc ceramic can be used to reduce the rate-of-rise.
Status Indicator Outputs
The N-Channel open drain output transistors can be used to
indicate which supply is connected, or can be used to drive
external PNP transistors to increase the power switching
capability of the circuit. When using external PNP power
transistors, the output current is limited by the beta and
thermal characteristics of the power transistors. The
application section details the use of external PNP
transistors.
Applications
A typical discrete battery backup circuit is illustrated in Figure
6. This approach requires several components, substantial
printed circuit board space, and high labor cost. It also
consumes a fairly high quiescent current. The ICL7673
battery backup circuit, illustrated in Figure 7, will often replace
such discrete designs and offer much better performance,
higher reliability, and lower system manufacturing cost. A
trickle charge system could be implemented with an additional
resistor and diode as shown in Figure 8. A complete low
power AC to regulated DC system can be implemented using
the ICL7673 and ICL7663S micropower voltage regulator as
shown in Figure 9.
+5V
PRIMARY
DC POWER
VO
+5V OR
+3V
STATUS
INDICATOR
NiCAD
BATTERY
STACK
GND
FIGURE 6. DISCRETE BATTERY BACKUP CIRCUIT
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.
+5V
PRIMARY
SUPPLY
8
VP
1
VO
VO
+5V OR +3V
LITHIUM
BATTERY
GND
2 VS
Pbar 6
GND
+
4
-
RI
STATUS
INDICATOR
FIGURE 7. ICL7673 BATTERY BACKUP CIRCUIT
+5V
PRIMARY
SUPPLY
RC
RECHARGEABLE
BATTERY
GND
8
VP
1
VO
2 VS
+
GND
4
-
VO
+5V OR +3V
FIGURE 8. APPLICATION REQUIRING RECHARGEABLE
BATTERY BACKUP
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 VP
and VS, with the circuit output VO supplying power to the
clock or volatile memory. The ICL7673 will sense the main
supply, when energized, to be of greater potential than VS
and connect, via its internal MOS switches, VP to output VO.
The backup input, VS will be disconnected internally. In the
event of main supply failure, the circuit will sense that the
backup supply is now the greater potential, disconnect VP
from VO, and connect VS.
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 VP and
open drain output SBAR through a resistor as illustrated in
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.
3-85
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