LM3410 datasheet(10/49 Pages) TI1

10 / 49 page

VFB

RSET

= ILED

ILED

VFB

RSET

LM3410, LM3410Q

SNVS541G – OCTOBER 2007 – REVISED MAY 2013

www.ti.com

Design Guide

SETTING THE LED CURRENT

Figure 16. Setting ILED

The LED current is set using the following equation:

where

•

RSET is connected between the FB pin and GND.

(1)

DIM PIN / SHUTDOWN MODE

The average LED current can be controlled using a PWM signal on the DIM pin. The duty cycle can be varied

between 0 and 100% to either increase or decrease LED brightness. PWM frequencies in the range of 1 Hz to

25 kHz can be used. For controlling LED currents down to the µA levels, it is best to use a PWM signal

frequency between 200 and 1 kHz. The maximum LED current would be achieved using a 100% duty cycle, i.e.

the DIM pin always high.

LED-DRIVE CAPABILITY

When using the LM3410 in the typical application configuration, with LEDs stacked in series between the VOUT

and FB pin, the maximum number of LEDs that can be placed in series is dependent on the maximum LED

forward voltage (VFMAX).

(VFMAX x NLEDs) + 190 mV < 24V

(2)

When inserting a value for maximum VFMAX the LED forward voltage variation over the operating temperature

range should be considered.

THERMAL SHUTDOWN

Thermal shutdown limits total power dissipation by turning off the output switch when the IC junction temperature

exceeds 165°C. After thermal shutdown occurs, the output switch doesn’t turn on until the junction temperature

drops to approximately 150°C.

INDUCTOR SELECTION

The inductor value determines the input ripple current. Lower inductor values decrease the physical size of the

inductor, but increase the input ripple current. An increase in the inductor value will decrease the input ripple

current.

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