10

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FPF2123-FPF2125 Rev. C

Application Information

Typical Application

OFF ON

ON

GND

FPF2123- FPF2125

ISET

Battery

1.8V-5.5V

C1 = 10

µF

R1 = 100K

Ω

C2 = 0.1

µF

LOAD

R2 = 499

Ω

Setting Current Limit

The FPF2123, FPF2124, and FPF2125 have a current limit

which is set with an external resistor connected between ISET

and GND. This resistor is selected by using the following

equation,

application would be the 500mA current that is required by a

single USB port. Using the table below an appropriate selection

port load could draw 570mA, but not more than 950mA.

deliver at least 1120mA and never more than 1860mA.

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

capacitance or a short-circuit, a capacitor needs to be placed

be used to further reduce the voltage drop.

Output Capacitor

GND. This capacitor will prevent parasitic board inductances

the FPF2123 and FPF2124, the total output capacitance needs

part from registering an over-current condition and turning-off

the switch. The maximum output capacitance can be

determined from the following formula,

Power Dissipation

During normal operation as a switch, the power dissipated in the

part will depend upon the level at which the current limit is set.

The maximum allowed setting for the current limit is 1.5A and

this will result in a typical power dissipation of,

If the part goes into current limit the maximum power dissipation

will occur when the output is shorted to ground.

For the

FPF2123 the power dissipation will scale by the Auto-Restart

so that the maximum power dissipated is,

LIM

SET

I

460

R

=

IN

BLANK

LIM

OUT

V

(min)

t

(max)

I

(max)

C

∗

=

[

Ω]

Min. Current

Limit

[mA]

Typ. Current

Limit

[mA]

Max. Current

Limit

[mA]

309

1120

1490

1860

340

1010

1350

1690

374

920

1230

1540

412

840

1120

1400

453

760

1010

1270

499

690

920

1150

549

630

840

1050

576

600

800

1000

604

570

760

950

732

470

630

790

887

390

520

650

1070

320

430

540

1300

260

350

440

1910

180

240

300

3090

110

150

190

81mW

2

0.125

(1.5)

R

)

(I

P

2

2

ON

LIM

=

∗

=

∗

=

(2)

(1)

(3)