LM3410YSDX National Semiconductor Corporation, LM3410YSDX Datasheet - Page 18

• Manufacturer Part Number: LM3410YSDX
• Description: Lm3410/lm3410q 525khz/1.6mhz, Constant Current Boost And Sepic Led Driver With Internal Compensation
• Manufacturer: National Semiconductor Corporation

www.national.com
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.
I
L1
= (I
I
L2
LED
= (I
and
) x (D/D')
LED
)
FIGURE 15. SEPIC Simplified Schematic
18
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.
TABLE 3. Efficiencies for Typical SEPIC Applications
V
I
V
LED
I
OUT
IN
η
IN
FIGURE 16. HB/OLED SEPIC PCB Layout
770mA
500mA
2.7V
3.1V
75%
V
I
V
LED
I
OUT
η
IN
IN
600mA
500mA
3.3V
3.1V
80%
V
I
30038559
V
LED
I
OUT
η
30038565
IN
IN
375mA
500mA
3.1V
83%
5V