LM3410_08 Datasheet, PDF (18/32 Pages) National Semiconductor (TI) – PowerWise® 525kHz/1.6MHz, Constant Current Boost and SEPIC LED Driver with Internal Compensation

Steady State Analysis with Loss
Elements
FIGURE 15. SEPIC Simplified Schematic
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Using inductor volt-second balance & capacitor charge bal-
ance, the following equations are derived:
I_L2 = (I_LED)
and
I_L1 = (I_LED) x (D/D')
TABLE 3. Efficiencies for Typical SEPIC Applications
V_IN
V_OUT
I_IN
I_LED
η
2.7V
3.1V
770mA
500mA
75%
V_IN
V_OUT
I_IN
I_LED
η
3.3V
3.1V
600mA
500mA
80%
V_IN
V_OUT
I_IN
I_LED
η
5V
3.1V
375mA
500mA
83%
SEPIC Converter PCB Layout
The layout guidelines described for the LM3410 Boost-Con-
verter are applicable to the SEPIC OLED Converter. Figure
16 is a proper PCB layout for a SEPIC Converter.
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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FIGURE 16. HB/OLED SEPIC PCB Layout
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