FPF2104(2005) 查看數據表（PDF） - Fairchild Semiconductor

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FPF2104
(Rev.:2005)

IntelliMAX™ Advanced Load Management Products

Fairchild Semiconductor 

Application Information

Typical Application

Battery

1.8V-5.5V

OFF ON

C1 = 10µF

VIN

VOUT

FPF2100 - FPF2107

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 VIN and GND. A 0.1uF ceramic capacitor, CIN, placed

close to the pins is usually sufficient. Higher values of CIN can

be used to further reduce the voltage drop.

Output Capacitor

A 0.1uF capacitor COUT, should be placed between VOUT and

GND. This capacitor will prevent parasitic board inductances

from forcing VOUT below GND when the switch turns-off. For

the FPF2100-FPF2102 and the FPF2104-FPF2106, the total

output capacitance needs to be kept below a maximum value,

COUT(max), to prevent the part from registering an over-current

condition and turning off the switch. The maximum output

capacitance can be determined from the following formula,

C OUT (max) = ILIM (max) ∗ tBLANK (min)

(1)

V IN

Due to the integral body diode in the PMOS switch, a CIN

greater than COUT is highly recommended. A COUT greater

than CIN can cause VOUT to exceed VIN when the system

supply is removed. This could result in current flow through the

body diode from VOUT to VIN.

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

(2)

If the part goes into current limit the maximum power dissipation

will occur when the output is shorted to ground. For the

FPF2100, FPF2101, FPF2104 and FPF2105, the power

dissipation will scale by the Auto-Restart Time, tRSTRT, and the

Over Current Blanking Time, tBLANK, so that the maximum

power dissipated is typically,

P(max) =

tBLANK

∗ VIN(max) ∗ILIM(max)

t + t RETRY BLANK

= 10 ∗ 5.5 ∗ 0.8 = 260mW (3)

10 + 160

When using the FPF2102 and FPF2106 attention must be given

to the manual resetting of the part. Continuously resetting the

part at a high duty cycle when a short on the output is present

can cause the temperature of the part to increase. The junction

temperature will only be allowed to increase to the thermal

shutdown threshold. Once this temperature has been reached,

toggling ON will not turn on the switch until the junction

temperature drops. For the FPF2103 and FPF2107, a short on

the output will cause the part to operate in a constant current

state dissipating a worst case power as calculated in (3) 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 VIN, VOUT and GND will help

minimize parasitic electrical effects along with minimizing the

case to ambient thermal impedance.

10

FPF2100-FPF2107 Rev. D2

www.fairchildsemi.com

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