LM3424 datasheet(34/69 Pages) TI1

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P =

r x

P =

r x

1 Z

SLP

LIM

1.5x10

x L1

V xR xR

LIM

245 mV

1-DMAX

DMAX

ICO-RMS = ILED x

RMS

LED

LM3424, LM3424-Q1

SNVS603C – AUGUST 2009 – REVISED AUGUST 2015

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Typical Applications (continued)

To set the worst case LED ripple current, use DMAX when solving for CO. Remember, when PWM dimming it is

recommended to use a minimum of 40 µF of output capacitance to improve performance.

The minimum allowable RMS output capacitor current rating (ICO-RMS) can be approximated:

Buck

(52)

Boost and Buck-Boost

(53)

8.2.1.2.7

Peak Current Limit

Set the peak current limit (ILIM) by solving for the transistor path sense resistor (RLIM):

(54)

8.2.1.2.8

Slope Compensation

For all topologies, the preferred method to set slope compensation is to ensure any duty cycle is attainable for

the nominal VO and chosen L by solving for RSLP:

(55)

8.2.1.2.9

Loop Compensation

Using a simple first order peak current mode control model, neglecting any output capacitor ESR dynamics, the

necessary loop compensation can be determined.

First, the uncompensated loop gain (TU) of the regulator can be approximated:

Buck

(56)

Boost and Buck-Boost

(57)

Where the pole (

ωP1) is approximated:

Buck

(58)

Boost

(59)

Buck-Boost

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