Datasheet


SLUS599A − JUNE 2004 − REVISED AUGUST 2008
6
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APPLICATION INFORMATION
When the TPS2400 disconnects the load from the power supply, the power-supply output-voltage spikes as the
stored energy in inductor L
S
is released. A zener diode D1 or a small ceramic capacitor can be used to keep
the voltage spike at a safe level.
AppliancePower Supply
+
LOAD
F2S1
D1
(Optional)
U1
TPS2400
5
4
2
D2
(Optional)
V
S
L
S
R
S
F1
Q1
UDG−04058
Figure 3. TPS2400 Application Block Diagram
Controlling the Load Inrush-Current
Figure 4 is a simplified representation of an appliance with a plug-in power supply (e.g., wall adapter). When
power is first applied to the load in Figure 4, the large filter capacitor C
LOAD
acts like a short circuit, producing
an immediate inrush-current that is limited by the power-supply output resistance and inductance, R
S
and L
S
,
respectively.
This current can be several orders of magnitude greater than the steady-state load current. The
large inrush current can damage power connectors P1 and J1 and power switch S1, and stress components.
Increasing the power-supply output resistance and inductance lowers the inrush current. However, the former
increases system power-dissipation and the latter decreases connector and switch reliability by encouraging
the contacts to arc when they bounce.
V
S
L
S
R
S
F1
UDG−04059
C
LOAD
AppliancePower Supply
+
LOAD
F2S1J1 P1
Figure 4. Power-Supply Output Resistance and Inductance Circuit Model