LM3410YSDX National Semiconductor Corporation, LM3410YSDX Datasheet - Page 7

• Manufacturer Part Number: LM3410YSDX
• Description: Lm3410/lm3410q 525khz/1.6mhz, Constant Current Boost And Sepic Led Driver With Internal Compensation
• Manufacturer: National Semiconductor Corporation

Simplified Internal Block Diagram
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
FIGURE 1. Simplified Block Diagram
7
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 (V
imately GND, and the inductor current (I
linear slope. I
which generates an output proportional to the switch current.
The sensed signal is summed with the regulator’s corrective
ramp and compared to the error amplifier’s output, which is
proportional to the difference between the feedback voltage
and V
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 (V
regulator loop adjusts the duty cycle (D) to maintain a regu-
lated LED current.
REF
. When the PWM comparator output goes high, the
L
is measured by the current sense amplifier,
SW
) decreases to approx-
30038514
L
D
) increases with a
) of the diode. The
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