LM3410XMFE datasheet(11/49 Pages) TI

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VOUT - KVIN

D =

VOUT

VOUT x ILED

K =

VIN x IIN

'¶

VOUT

VIN

VOUT - VIN

D =

VOUT

1 - D

VOUT

VIN

2'iL

DTS

L =

¨¨

VIN

¸¸

¨¨

VIN

¸¸

x DTS

( )

VIN

OUT

IN -

LM3410, LM3410Q

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SNVS541G – OCTOBER 2007 – REVISED MAY 2013

Figure 17. Inductor Current

(3)

The Duty Cycle (D) for a Boost converter can be approximated by using the ratio of output voltage (VOUT) to input

voltage (VIN).

(4)

Therefore:

(5)

Power losses due to the diode (D1) forward voltage drop, the voltage drop across the internal NMOS switch, the

voltage drop across the inductor resistance (RDCR) and switching losses must be included to calculate a more

accurate duty cycle (See Calculating Efficiency and Junction Temperature for a detailed explanation). A more

accurate formula for calculating the conversion ratio is:

Where

•

η equals the efficiency of the LM3410 application.

(6)

Or:

(7)

Therefore:

(8)

Inductor ripple in a LED driver circuit can be greater than what would normally be allowed in a voltage regulator

Boost and Sepic design. A good design practice is to allow the inductor to produce 20% to 50% ripple of

maximum load. The increased ripple shouldn’t be a problem when illuminating LEDs.

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