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| LM3409 Datasheet, PDF (18/30 Pages) National Semiconductor (TI) – PFET Buck Controller for High Power LED Drives | |||
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Design Example #1
EN PIN PWM DIMMING APPLICATION FOR 10 LEDS
SPECIFICATIONS
fSW = 525kHz
VIN = 48V; VIN-MAX = 75V
VO = 35V
ILED = 2A
ÎiLED-PP = ÎiL-PP = 1A
ÎvIN-PP = 1.44V
VTURN-ON = 10V; VHYS = 1.1V
η = 0.95
1. NOMINAL SWITCHING FREQUENCY
Assume COFF = 470pF and η = 0.95. Solve for ROFF:
30085618
The chosen components from step 1 are:
2. INDUCTOR RIPPLE CURRENT
Solve for L1:
The closest standard inductor value is 15 µH therefore the
actual ÎiL-PP is:
The closest 1% tolerance resistor is 24.9 k⦠therefore the
actual tOFF and target fSW are:
The chosen component from step 2 is:
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