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LTC4066EPF View Datasheet(PDF) - Linear Technology

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LTC4066/LTC4066-1
APPLICATIONS INFORMATION
In USB applications, the minimum value for RCLPROG
should be 2.1k. This will prevent the application current
from exceeding 500mA due to LTC4066/LTC4066-1 toler-
ances and quiescent currents. A 2.1k CLPROG resistor will
give a typical current limit of 476mA in high power mode
(HPWR = 1) or 95mA in low power mode (HPWR = 0).
VCLPROG will typically servo to 1V; however, if IOUT + IBAT
< ICL then VCLPROG will track the input current according
to the following equation:
IIN
=
VCLPROG
RCLPROG
1000
For best stability over temperature and time, 1% metal
film resistors are recommended.
Ideal Diode from BAT to OUT
If a battery is the only power supply available or if the load
current exceeds the programmed input current limit, then
the battery will automatically deliver power to the load via
an ideal diode circuit between the BAT and OUT pins. The
ideal diode circuit (along with the recommended 4.7μF
capacitor on the OUT pin) allows the LTC4066/LTC4066-1
to handle large transient loads and wall adapter or USB
VBUS connect/disconnect scenarios without the need for
large bulk capacitors. The ideal diode responds within a
few microseconds and prevents the OUT pin voltage from
dipping below the BAT pin voltage by more than 50mV.
Forward regulation for the ideal diode from BAT to OUT
has three operational ranges, depending on the magni-
tude of the diode load current. For small load currents,
the LTC4066/LTC4066-1 will provide a constant voltage
drop; this operating mode is referred to as “constant
VON” regulation. As the current exceeds IFWD the voltage
drop will increase linearly with the current with a slope of
1/RDIO(ON); this operating mode is referred to as “constant
RON” regulation. As the current increases further, exceeding
IMAX, the forward voltage drop will increase rapidly; this
operating mode is referred to as “constant ION” regulation.
The characteristics for parameters RFWD, RON, VFWD and
IFWD are specified with the aid of Figure 3.
IMAX
LTC4066
CONSTANT
ION
SLOPE: 1/RDIO(ON)
CONSTANT
RON
IFWD
SLOPE: 1/RFWD
SCHOTTKY
DIODE
CONSTANT
VON
0
VFWD
FORWARD VOLTAGE (V)
4066 F03
Figure 3. LTC4066/LTC4066-1 vs Schottky Diode Forward Voltage Drop
4066fc
16
 

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