Datasheet


SLUS599A − JUNE 2004 − REVISED AUGUST 2008
7
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APPLICATION INFORMATION
The TPS2400 circuit in Figure 5 limits the inrush current without these draw backs. The TPS2400 charges the
transistor Q1 gate capacitance C
G
with a 5-µA source when Q1 is commanded to turn on. Transistor Q1 is wired
as a source follower so the gate-voltage slew rate and the load-voltage slew rate are identical and equal to
ēV
L
ēt
+
5 mA
C
G
The corresponding inrush current is:
I
INRUSH
[ C
L
ēV
L
ēt
+
ǒ
C
L
C
G
Ǔ
5 mA
An external capacitor and a series 1-kΩ resistor can be connected to the gate of Q1 and ground to reduce inrush
current further. In this case, the parameter C
G
in equations 1 and 2 is the sum of the internal and external FET
gate capacitance. The 1-kΩ resistor decouples the external gate capacitor so the TPS2400 can rapidly turn off
transistor Q1 in response to an overvoltage condition.
UDG−04060
C
LOAD
L
S
R
S
F1
Q1
AppliancePower Supply
+
LOAD
F2S1
D1
(Optional)
U1
TPS2400
5
4
2
J1 P1
Figure 5. Turn-On Voltage Slew Rate Control Using the TPS2400
(1)
(2)