Datasheet

IADJ
EN
CSN
LM3409HV
UVLO
D1
L1
V
IN
= 48V
I
LED
= 2A
VCC
COFF
GND
Q1
CSP
C
F
R
OFF
PGATE
C
OFF
R
UV2
R
UV1
DAP
VIN
V
O
= 35V
R
SNS
1
2
3
4
5 6
7
8
9
10
PWM
C
IN1
C
IN2
PA
1
R
EXT
=
I
LED
+
¨
©
§
2
x R
SNS
¸
¹
·
i
L-PP
'
LM3409, LM3409HV, LM3409-Q1
www.ti.com SNVS602J –MARCH 2009–REVISED MAY 2013
(44)
10. PWM DIMMING METHOD
There are two methods to PWM dim using the LM3409/09HV:
Method #1: Apply an external PWM signal to the EN terminal.
Method #2: Perform external parallel FET shunt dimming as detailed in the EXTERNAL PARALLEL FET PWM
DIMMING section.
Design Example #1
EN PIN PWM DIMMING APPLICATION FOR 10 LEDS
SPECIFICATIONS
f
SW
= 525kHz
V
IN
= 48V; V
IN-MAX
= 75V
V
O
= 35V
I
LED
= 2A
Δi
LED-PP
= Δi
L-PP
= 1A
Δv
IN-PP
= 1.44V
V
TURN-ON
= 10V; V
HYS
= 1.1V
η = 0.95
1. NOMINAL SWITCHING FREQUENCY
Assume C
OFF
= 470pF and η = 0.95. Solve for R
OFF
:
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