ICL7673CBA Intersil, ICL7673CBA Datasheet - Page 4

• Manufacturer Part Number: ICL7673CBA
• Description: IC SWITCH BATTERY BACKUP 8-SOIC
• Manufacturer: Intersil

Specifications of ICL7673CBA

• Applications: Battery Backup, Industrial/Automotive, High Current Switch
• Fet Type: N and P-Channel
• Number Of Outputs: 1
• Internal Switch(s): Yes
• Voltage - Supply: 2.5 V ~ 15 V
• Current - Supply: 1.5µA
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Delay Time - On: -
• Delay Time - Off: -

Detailed Description
As shown in the Functional Diagram, the ICL7673 includes a
comparator which senses the input voltages V
output of the comparator drives the first inverter and the
open-drain N-Channel transistor P
drives a large P-Channel switch, P
another open-drain N-Channel transistor, S
inverter drives another large P-Channel switch P
ICL7673, connected to a main and a backup power supply,
will connect the supply of greater potential to its output. The
circuit provides break-before-make switch action as it
switches from main to backup power in the event of a main
power supply failure. For proper operation, inputs V
must not be allowed to float, and, the difference in the two
supplies must be greater than 50mV. The leakage current
through the reverse biased parasitic diode of switch P
very low.
Output Voltage
The output operating voltage range is 2.5V to 15V. The
insertion loss between either input and the output is a
function of load current, input voltage, and temperature. This
is due to the P-Channels being operated in their triode
region, and, the ON-resistance of the switches is a function
of output voltage V
have positive temperature coefficients, and therefore as
temperature increases the insertion loss also increases. At
1000pA
100mA
FIGURE 5. I
10nA
10pA
1mA
1nA
1pA
0
FUNCTION OF INPUT VOLTAGE
S
LEAKAGE CURRENT V
2
I
V
O
LOAD
S
. The ON-resistance of the P-Channels
= 0V
= 10mA
4
INPUT V
5
4
6
BAR
1
P
, a second inverter, and
(V)
P
. The first inverter
TO V
8
BAR
S
P
AS A
. The second
and V
2
10
. The
P
85°C
25°C
and V
S
2
. The
is
12
S
ICL7673
low load currents the output voltage is nearly equal to the
greater of the two inputs. The maximum voltage drop across
switch P
drain parasitic diode will become forward biased. Complete
switching of the inputs and open-drain outputs typically
occurs in 50µs.
Input Voltage
The input operating voltage range for V
15V. The input supply voltage (V
limited to 2V per microsecond to avoid potential harm to the
circuit. In line-operated systems, the rate-of-rise (or fall) of
the supply is a function of power supply design. For battery
applications it may be necessary to use a capacitor between
the input and ground pins to limit the rate-of-rise of the
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.
DC POWER
PRIMARY
FIGURE 6. DISCRETE BATTERY BACKUP CIRCUIT
GND
1
+5V
or P
2
is 0.5V, since above this voltage the body-
NiCAD
BATTERY
STACK
P
or V
S
P
) slew rate should be
or V
S
is 2.5V to
+5V OR
+3V
V
STATUS
INDICATOR
O
July 22, 2005
FN3183.4