LM3410_08 Datasheet, PDF(8/32 Page) National Semiconductor (TI) – PowerWise® 525kHz/1.6MHz, Constant Current Boost and SEPIC LED Driver with Internal Compensation

English

English German Russian Spanish Italian Polish Chinese Japanese Korean French Portuguese	Language :

LM3410_08 Datasheet, PDF (8/32 Pages) National Semiconductor (TI) – PowerWise® 525kHz/1.6MHz, Constant Current Boost and SEPIC LED Driver with Internal Compensation

◁

Simplified Internal Block Diagram

FIGURE 1. Simplified Block Diagram

30038514

Application Information

THEORY OF OPERATION

The LM3410 is a constant frequency PWM, boost regulator

IC. It delivers a minimum of 2.1A peak switch current. The

device operates very similar to a voltage regulated boost con-

verter except that it regulates the output current through

LEDs. The current magnitude is set with a series resistor. This

series resistor multiplied by the LED current creates the feed-

back voltage (190 mV) which the converter regulates to. The

regulator has a preset switching frequency of either 525 kHz

or 1.60 MHz. This high frequency allows the LM3410 to op-

erate with small surface mount capacitors and inductors,

resulting in a DC/DC converter that requires a minimum

amount of board space. The LM3410 is internally compen-

sated, so it is simple to use, and requires few external com-

ponents. The LM3410 uses current-mode control to regulate

the LED current. The following operating description of the

LM3410 will refer to the Simplified Block Diagram (Figure 1)

the simplified schematic (Figure 2), and its associated wave-

forms (Figure 3). The LM3410 supplies a regulated LED

current by switching the internal NMOS control switch at con-

stant frequency and variable duty cycle. A switching cycle

begins at the falling edge of the reset pulse generated by the

internal oscillator. When this pulse goes low, the output con-

trol logic turns on the internal NMOS control switch. During

this on-time, the SW pin voltage (VSW) decreases to approx-

imately GND, and the inductor current (IL) increases with a

linear slope. IL is measured by the current sense amplifier,

which generates an output proportional to the switch current.

The sensed signal is summed with the regulatorâs corrective

ramp and compared to the error amplifierâs output, which is

proportional to the difference between the feedback voltage

and VREF. When the PWM comparator output goes high, the

output switch turns off until the next switching cycle begins.

During the switch off-time, inductor current discharges

through diode D1, which forces the SW pin to swing to the

output voltage plus the forward voltage (VD) of the diode. The

regulator loop adjusts the duty cycle (D) to maintain a regu-

lated LED current.

www.national.com

▷