Datasheet

SHORT
ILIMx
48000
I
R
=
SHORT _ min
1.037
ILIMx
48000
I
R
=
SHORT _ max
0.962
ILIMx
48000
I
R
=
TPS2554
TPS2555
www.ti.com SLVSAM0 –JUNE 2011
APPLICATION INFORMATION
Input and Output Capacitance
Capacitance added to the input and output of the TPS2554/55 improves the performance of the device; the
actual capacitance should be optimized for the particular application. For all applications, a 100 nF or greater
ceramic bypass capacitor between IN and GND is recommended as close to the device as possible for local
noise decoupling. This precaution reduces ringing on the input due to power-supply transients. Additional input
capacitance may be needed on the input to prevent voltage overshoot from exceeding the absolute-maximum
voltage of the device during heavy transient conditions. This is especially important during bench testing when
long, inductive cables are used to connect the evaluation board to the bench power supply.
Output capacitance is not required for proper operation of the TPS2554/55, but placing a high-value electrolytic
capacitor on the output pin is recommended when large transient currents are expected on the output.
Programming the Current-Limit Threshold
Two overcurrent thresholds are user-programmable via two external resistors. The recommended 1% resistor
range for R
ILIMx
is 16.9 kΩ ≤ R
ILIM
≤ 750 kΩ to ensure stability of the internal regulation loop. Best accuracy is
obtained with R
ILIMx
values less than 210 kΩ. Many applications require that the minimum current limit is above a
certain current level or that the maximum current limit is below a certain current level, so it is important to
consider the tolerance of the overcurrent threshold when selecting a value for R
ILIMx
. The following equations
approximate the resulting overcurrent threshold for a given external resistor value, R
ILIMx
. Consult the Electrical
Characteristics table for specific current-limit settings. Printed-circuit-board traces routing the R
ILIMx
resistor to the
TPS2554/55 should be as short as possible to reduce parasitic effects on the current-limit accuracy.
The equations and the graph below can be used to estimate the minimum and maximum variation of the
current-limit threshold for a predefined resistor value. This variation is an approximation only and does not take
into account, for example, the resistor tolerance. For examples of more-precise variation of I
SHORT
refer to the
current-limit section of the Electrical Characteristics table.
(2)
(3)
(4)
• I
SHORT
= Current-limit threshold, mA
• R
ILIM
= Resistance at ILIMx pin, kΩ
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Product Folder Link(s): TPS2554 TPS2555