Datasheet

( )
straightwire VIN
4 L
L 0.2 L V 0.75 nH
D
´
æ ö
» ´ ´ -
ç ÷
è ø
( )
NOM LOAD
SPIKE absolute
L
V V I
C
= + ´
TPS2421-1
TPS2421-2
SLUS907H –JANUARY 2009–REVISED JANUARY 2014 www.ti.com
The following equation estimates the magnitude of these voltage spikes:
where
• V
NOM
is the nominal supply voltage
• I
LOAD
is the load current
• C is the capacitance present at the input or output of the TPS2421 device
• L equals the effective inductance seen looking into the source or the load (20)
Calculating the inductance due to a straight length of wire is shown in Equation 21.
where
• L is the length of the wire
• D is diameter of the wire (21)
Some applications may require the addition of a TVS to prevent transients from exceeding the absolute ratings if
sufficient capacitance cannot be included.
Layout
Support Components
Locate all TPS2421 support components, R
RSET
, C
CT
, or any input or output voltage clamps, close to their
connection pin. Connect the other end of the component to the inner layer GND without trace length. The trace
routing the R
RSET
resistor to the TPS2421 device must be as short as possible to reduce parasitic effects on fault
and current-limit accuracy.
PowerPad™
When properly mounted the PowerPad package provides significantly greater cooling ability than an ordinary
package. To operate at rated power the Power Pad must be soldered directly to the PC board GND plane
directly under the device. The PowerPad is at GND potential and can be connected using multiple vias to inner
layer GND. Other planes, such a the bottom side of the circuit board can be used to increase heat sinking in
higher current applications. Refer to Technical Briefs: PowerPad™ Thermally Enhanced Package (SLMA002)
and PowerPad™ Made Easy (SLMA004) or more information on using this PowerPad™ package. These
documents are available at www.ti.com (Search by Keyword).
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Product Folder Links: TPS2421-1 TPS2421-2