Datasheet

IADJ
EN
CSN
LM3409/HV
UVLO
D1
L1
C
IN
V
IN
I
LED
VCC
COFF
GND
Q1
CSP
C
F
R
OFF
PGATE
C
OFF
R
UV2
R
UV1
DAP
VIN
V
O
R
SNS
1
2
3
4
5 6
7
8
9
10
LM3409, LM3409HV, LM3409-Q1
SNVS602J –MARCH 2009–REVISED MAY 2013 www.ti.com
Design Guide
TYPICAL APPLICATION
SPECIFICATIONS
Nominal input voltage: V
IN
Maximum input voltage: V
IN-MAX
Nominal output voltage (# of LEDs x forward voltage): V
O
LED string dynamic resistance: r
D
Switching frequency (at nominal V
IN
, V
O
): f
SW
Average LED current: I
LED
Inductor current ripple: Δi
L-PP
LED current ripple: Δi
LED-PP
Input voltage ripple: Δv
IN-PP
UVLO characteristics: V
TURN-ON
and V
HYS
Expected efficiency: η
1. NOMINAL SWITCHING FREQUENCY
Calculate switching frequency (f
SW
) at the nominal operating point (V
IN
and V
O
). Assume a C
OFF
value (between
470pF and 1nF) and a system efficiency (η). Solve for R
OFF
:
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