LM3409MYX National Semiconductor Corporation, LM3409MYX Datasheet - Page 21

• Manufacturer Part Number: LM3409MYX
• Description: Pfet Buck Controller For High Power Led Drives
• Manufacturer: National Semiconductor Corporation

Design Example #2
ANALOG DIMMING APPLICATION FOR 4 LEDS
SPECIFICATIONS
f
V
V
I
Δi
Δv
V
η = 0.90
1. NOMINAL SWITCHING FREQUENCY
Assume C
The closest 1% tolerance resistor is 15.4 kΩ therefore the
actual t
SW
LED
IN
O
TURN-ON
L-PP
IN-PP
= 14V
= 500kHz
= 24V; V
= 1A
= 450mA; Δi
OFF
= 1V
= 10V; V
OFF
and target f
IN-MAX
= 470pF and η = 0.90. Solve for R
HYS
= 42V
LED-PP
= 1.1V
SW
= 50mA
are:
OFF
:
21
The chosen components from step 1 are:
2. INDUCTOR RIPPLE CURRENT
Solve for L1:
The closest standard inductor value is 22 µH therefore the
actual Δi
The chosen component from step 2 is:
L-PP
is:
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