Datasheet

OUT D
OUT D IN
V V
D
V V V
+
=
+ +
VIN
6-18V
VIN
VIN
12V, 1A
49.9
86.6k
1
1
Not Populated
TP3
SYNC
SYNC
TP2
TP5
TP4
Lb
La
TPS55340
www.ti.com SLVSBD4B –MAY 2012–REVISED OCTOBER 2012
DESIGN GUIDE-STEP-BY-STEP DESIGN PROCEDURE OF SEPIC CONVERTER
Figure 24. SEPIC Converter Application Schematic
The following parameters are used for a SEPIC converter design. These calculations are performed only for
CCM operation, and the use of a coupled inductor is assumed.
Table 2. Key Parameters of SEPIC Converter Example
PARAMETER VALUE
Output Voltage 12 V
Input Voltage 6 V to 18 V, 12 V nominal
Maximum Output Current 1 A
Transient Response 50% load step (ΔV
OUT
= 4%) 480 mV
Output Voltage Ripple (0.5% of V
OUT
) 60 mV
SELECTING THE SWITCHING FREQUENCY (R4)
A 500 kHz switching frequency (ƒ
SW
) is selected for this design. Using Equation 1, R4 is calculated and the
nearest standard value 95.3 kΩ is used.
DUTY CYCLE
The duty cycle of a SEPIC converter is calculated with Equation 40. With the 6 V minimum input the duty cycle is
68% and with the 18 V maximum input voltage the duty cycle is 41%.
(40)
Copyright © 2012, Texas Instruments Incorporated Submit Documentation Feedback 21
Product Folder Links :TPS55340