lm2735xsdx National Semiconductor Corporation, lm2735xsdx Datasheet - Page 19

• Manufacturer Part Number: lm2735xsdx
• Description: 520khz/1.6mhz - Space-efficient Boost And Sepic Dc-dc Regulator
• Manufacturer: National Semiconductor Corporation

Steady State Analysis with Loss
Elements
Using inductor volt-second balance & capacitor charge bal-
ance, the following equations are derived:
Therefore:
One can see that all variables are known except for the duty
cycle (D). A quadratic equation is needed to solve for D. A
less accurate method of determining the duty cycle is to as-
sume efficiency, and calculate the duty cycle.
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SEPIC Converter PCB Layout
The layout guidelines described for the LM2735 Boost-Con-
verter are applicable to the SEPIC Converter. Below is a
proper PCB layout for a SEPIC Converter.
LLP Package
The LM2735 packaged in the 6–pin LLP:
For certain high power applications, the PCB land may be
modified to a "dog bone" shape (see Figure 19). Increasing
the size of ground plane, and adding thermal vias can reduce
the R
θJA
Efficiencies for Typical SEPIC Application
for the application.
FIGURE 18. Internal LLP Connection
FIGURE 19. PCB Dog Bone Layout
FIGURE 17. SEPIC PCB Layout
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