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FPF2193 View Datasheet(PDF) - ON Semiconductor

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FPF2193 Datasheet PDF : 14 Pages
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Application Information
Figure 28. Typical Application
Setting Current Limit
The FPF2193, FPF2194, and FPF2195 current limit is
set w ith an external resistor connected betw een ISET and
GND. This resistor is selected using the follow ing
equation:
RSET
551.6
ILIM
(1)
RSET is in and ISET is in Amps.
Table 1 can also be used to select RSET. A typical
application w ould be the 500 mA current required by a
single USB port. Using Table 1, an appropriate selection
for the RSET resistor w ould be 788 Ω. This ensures that
the port load could draw 525 mA, but not more than
875 mA. Likew ise for a dual-port system; an RSET of
368 Ω alw ays delivers at least 1125 mA and never more
than 1875 mA.
Table 1. Current Lim it Various RSET Values
Input Capacitor
To limit the voltage drop on the input supply caused by
transient inrush currents w hen the sw itch is turned on
into a discharged load capacitor or a short-circuit, a
capacitor needs to be placed betw een V IN and GND. A
0.1 µF 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 0.1 µF capacitor, COUT, should be placed betw een
VOUT and GND. This capacitor prevents parasitic board
inductances from forcing VOUT below GND w hen the
sw itch turns off. For the FPF2193 and FPF2194, 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
sw itch. The maximum output capacitance can be
determined from the follow ing formula:
RSET()
Min. Current
Lim it (m A)
368
1125
Typ. Current
Lim it (m A)
1500
Max. Current
Lim it (m A)
1875
COUT
(max)
ILIM(max)tBLANK(min)
VIN
(2)
441
928
552
750
613
675
690
600
788
525
919
450
1103
375
1226
338
1379
300
1576
263
1839
225
2206
188
2758
150
3677
113
5516
75
15800(4)
35
1250
1000
900
800
700
600
500
450
400
350
300
250
200
150
100
45
1562
1250
1125
1000
875
750
625
563
500
438
375
313
250
188
125
60
Power Dissipation
During normal operation as a sw itch, the pow er
dissipated depends upon the level at w hich the current
limit is set. The maximum allow ed setting for the current
limit is 1.5 A and results in a pow er dissipation of :
P (ILIM)2 RON (1.5)2 0.055 123.75mW (3)
If the part goes into current limit, the maximum pow er
dissipation occurs w hen the output is shorted to ground.
For the FPF2193, the pow er dissipation scales by the
auto-restart time, tRSTRT, and the over-current blanking
time, tBLANK, so that the maximum pow er dissipated is:
P(max)
tBLANK
tBLANK tRSTRT
VIN(max)ILIM(max)
(4)
30 5.5 1.5 515.6mW
30 450
Note :
4. FPF2195BUCX only.
www.onsemi.com
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