LM3409MY-NOPB Datasheet, PDF (23/43 Pages) Texas Instruments – PFET Buck Controller for High Power LED Drivers

LM3409, LM3409HV, LM3409-Q1
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R_{EXT =}
¨©§I_LED
+
'i_L-PP¸·
2_¹
x
R_SNS
1 PA
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
R_UV2
R_UV1
1
UVLO
2
IADJ
10
VIN
C_F
9
VCC
PWM
R_OFF
C_OFF
3
EN
LM3409HV
8
CSP
4
COFF
5
GND
DAP
7
CSN
6
PGATE
R_SNS
Q1
L1
C_IN1 C_IN2
V_IN = 48V
V_O = 35V
I_LED = 2A
D1
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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