FPF2108 Datasheet, PDF (10/12 Pages) Fairchild Semiconductor – IntelliMAX Advanced Load Management Products

Application Information
Typical Application
Battery
1.8V-5.5V
OFF ON
C1 = 10µF
V_IN
V_OUT
FPF2108 - FPF2110
ON
FLAGB
GND
R1 = 100KΩ
LOAD
C2 = 0.1µF
R2 = 499Ω
Input Capacitor
To limit the voltage drop on the input supply caused by transient
in-rush currents when the switch turns-on into a discharged load
capacitor or a short-circuit, a capacitor needs to be placed
between V_IN and GND. A 0.1uF ceramic capacitor, C_IN, placed
close to the pins is usually sufficient. Higher values of C_IN can
be used to further reduce the voltage drop.
Output Capacitor
A 0.1uF capacitor C_OUT, should be placed between V_OUT and
GND. This capacitor will prevent parasitic board inductances
from forcing V_OUT below GND when the switch turns-off.
Power Dissipation
During normal operation as a switch, the power dissipation is
small and has little effect on the operating temperature of the
part. The parts with the higher current limits will dissipate the
most power and that will only typically be,
P = (ILIM)² ∗RDS = (0.8)² ∗ 0.125 = 80mW
When in current limit the maximum power dissipation will occur
when the output is shorted to ground. A short on the output will
cause the part to operate in a constant current state until the
thermal shutdown activates. It will then cycle in and out of
thermal shutdown so long as the ON pin is active and the short
is present.
Board Layout
For best performance, all traces should be as short as possible.
To be most effective, the input and output capacitors should be
placed close to the device to minimize the effects that parasitic
trace inductances may have on normal and short-circuit
operation. Using wide traces for V_IN, V_OUT and GND will help
minimize parasitic electrical effects along with minimizing the
case to ambient thermal impedance.
10
FPF2108-FPF2110 Rev. B
www.fairchildsemi.com