Data Sheet
10
www.fairchildsemi.com
FPF2123-FPF2125 Rev. F
FPF2123-FPF2125 IntelliMAX™ Advanced Load Management Products
Application Information
Typical Application
OFF ON ON
V
IN
GND
FPF2123- FPF2125
ISET
V
OUT
Battery
5.5V
C1=4.7F
R
SET
C2=0.1F
R2=110
5.5V MAX
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,
R
SET
is in Ohms and that of I
LIM
is Amps
The table below can also be used to select R
SET
. A typical
application would be the 500mA current that is required by a
single USB port. Using the table below an appropriate selection
for the R
SET
resistor would be 604. This will ensure that the
port load could draw 570mA, but not more than 950mA.
Likewise for a dual port system, an R
SET
of 340 would always
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
between V
IN
and GND. A 4.7F ceramic capacitor, C
IN
, must be
placed close to the V
IN
pin. A higher value of C
IN
can be used to
further reduce the voltage drop experienced as the switch is
turned on into a large capacitive load.
Output Capacitor
A 0.1F 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. For the
FPF2123 and FPF2124, the total output capacitance needs to
be kept below a maximum value, C
OUT(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,
Current Limit Various R
SET
Values
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
Time, t
RESTART
, and the Over Current Blanking Time, t
BLANK
, so
that the maximum power dissipated is,
R
SET
460
I
LIM
----------=
C
OUT
max( )
I
LIM
min( ) t
BLANK
min( )×
V
IN
-----------------------------------------------------------------
=
R
SET
[]
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
P I
LIM
( )=
2
R
ON
× 1.5( )
2
0.125×= 281mW=
(4)
20
80 20+
-------------------
5.5× 1.5×= 1.65W=
P max( )
t
BLANK
max( )
t
RESTART
min( ) t
BLANK
max( )+
---------------------------------------------------------------------------------
V
IN
max( )× I
LIM
max( )×=