Rainbow-electronics MAX16834 Manual de usuario descargar pdf (Pagina 11)

MAX16834

High-Power LED Driver with Integrated High-Side LED

Current Sense and PWM Dimming MOSFET Driver

______________________________________________________________________________________ 11

Boost Configuration

In the boost converter (Figure 2), the average inductor

current varies with the line voltage. The maximum aver-

age current occurs at the lowest line voltage. For the

boost converter, the average inductor current is equal

to the input current.

Calculate maximum duty cycle using the below equation.

where V

LED

is the forward voltage of the LED string in

volts, V

is the forward drop of the rectifier diode D1 in

volts (approximately 0.6V), V

INMIN

is the minimum input

supply voltage in volts, and V

FET

is the average drain to

source voltage of the MOSFET Q1 in volts when it is on.

Use an approximate value of 0.2V initially to calculate

MAX

. A more accurate value of the maximum duty

cycle can be calculated once the power MOSFET is

selected based on the maximum inductor current.

Use the following equations to calculate the maximum

average inductor current IL

AVG

, peak-to-peak inductor

current ripple ∆I

, and the peak inductor current IL

amperes:

AVG

LED

MAX

−1

VVV

MAX

LED D

INMIN

LEDDFET

+−

NDRV

OFF

PWMDIM

SGND

R10

MAX16834

FLT

DIMOUT

SENSE+

OVP+

CLV

COMP

PGND

UVEN

RT/SYNC

REF

REFI

LED+

LEDs

LED-

Figure 2. Boost LED Driver

1 2 ... 6 7 8 9 10 11 12 13 14 15 16 ... 21 22

MAX16834 1

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Rainbow-electronics MAX16834 Manual de usuario Pagina 11

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