Datasheet
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TPS5401
www.ti.com
SLVSAB0 –DECEMBER 2010
APPLICATION INFORMATION
Typical Application
The TPS5401 is good for the E-meter application. The power supply design is a challenge work to E-meter
designers because it must get enough output current from a wide input voltage range with a limited input power.
For example, in China, a single-phase or three-phase E-meter must work properly with an input AC electricity
voltage range from 0.7 Un to 1.9 Un. Here Un is the phase voltage of 220 V. The input active power limit is 1.5
W. A typical power supply design uses a transformer followed by a rectifier bridge to get a low unregulated dc
voltage. Then a voltage regulator generates 5 V for the whole system. Considering the ac transformer has large
internal dc resistance and the following rectifier has a voltage drop, the output voltage of the rectifier circuit is
different between empty load and heavy load. So the input voltage for the voltage regulator within the whole ac
input voltage range may have a maximum-to-minimum ratio of 4. In this situation, a linear regulator is not suitable
due to its very low efficiency at high input voltage.
Figure 40 shows a typical TPS5401 application schematic for this requirement. The input range is set to 7.5 V to
35 V. With such a wide input voltage range, an inexpensive transformer with high dc resistance can be used to
save total cost.
Figure 40. Typical Application Schematic
Step-by-Step Design Procedure
The following design procedure can be used to select component values for the TPS5401. Alternately, the
SwitcherPro software may be used to generate a complete design. The SwitcherPro software uses an iterative
design procedure and accesses a comprehensive database of components when generating a design. This
section presents a simplified discussion of the design process. To begin the design process, a few parameters
must be decided upon. Table 3 lists the parameters the designer needs to know.
Table 3.
DESIGN PARAMETER EXAMPLE VALUE
Input voltage range 7.5 V to 35 V
Output voltage 5 V
Input ripple voltage 300 mV
Output ripple voltage 1% of V
OUT
Output transient response for 0 to 500-mA load step 4% of V
OUT
Maximum output current 500 mA
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