Datasheet

TPS54320
www.ti.com SLVS982A –AUGUST 2010–REVISED SEPTEMBER 2010
APPLICATION INFORMATION
Design Guide – Step-By-Step Design Procedure
This example details the design of a high frequency switching regulator using ceramic output capacitors. A few
parameters must be known in order to start the design process. These parameters are typically determined at the
system level. For this example, we start with the following known parameters:
PARAMETER VALUE
Output Voltage 3.3 V
Output Current 3 A
Transient Response 0.75 A (25%) load step ΔV
OUT
= 4 %
Input Voltage 12 V nominal, 8 V to 17 V
Output Voltage Ripple 1% (33 mV
PP
)
Start Input Voltage (Rising Vin) 6.806 V
Stop Input Voltage (Falling Vin) 4.824 V
Switching Frequency 480 kHz
Typical Application Schematic
The application schematic of Figure 34 was developed to meet the requirements above. This circuit is available
as the TPS54320EVM-513 evaluation module. The design procedure is given in this section. For more
information about Type II and Type III frequency compensation circuits, see Designing Type III Compensation for
Current Mode Step-Down Converters (SLVA352) and Design Calculator (SLVC219).
Figure 34. Typical Application Circuit
Operating Frequency
The first step is to decide on a switching frequency for the regulator. There is a trade off between higher and
lower switching frequencies. Higher switching frequencies may produce a smaller solution size using lower
valued inductors and smaller output capacitors compared to a power supply that switches at a lower frequency.
However, the higher switching frequency causes additional switching losses, which negatively impact the
converter’s efficiency and thermal performance. In this design, a moderate switching frequency of 480kHz is
selected to achieve both a small solution size and a high efficiency operation. This frequency is set using the
resistor at the RT/CLK pin (R3). Using Equation 4, the resistance required for a switching frequency of 480kHz is
102 kΩ. A 100kΩ resistor is used for this design.
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