LT3475IFE-PBF Ver la hoja de datos (PDF) - Linear Technology

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Fabricante

LT3475IFE-PBF

Dual Step-Down 1.5A LED Driver

Linear Technology 

LT3475/LT3475-1

PI FU CTIO S

RT (Pin 14): The RT pin is used to set the internal

oscillator frequency. Tie a 24.3k resistor from RT to GND

for a 600kHz switching frequency.

SHDN (Pin 16): The SHDN pin is used to shut down the

switching regulator and the internal bias circuits. The

2.6V switching threshold can function as an accurate

undervoltage lockout. Pull below 0.3V to shut down the

LT3475/LT3475-1. Pull above 2.6V to enable the LT3475/

LT3475-1. Tie to VIN if the SHDN function is unused.

REF (Pin 17): The REF pin is the buffered output of the

internal reference. Either tie the REF pin to the VADJ pin

for a 1.5A output current, or use a resistor divider to

generate a lower voltage at the VADJ pin. Leave this pin

unconnected if unused.

VC1, VC2 (Pins 18, 13): The VC pin is the output of the

internal error amp. The voltage on this pin controls the

peak switch current. Use this pin to compensate the

control loop.

VADJ1, VADJ2 (Pins 19, 12): The VADJ pin is the input to

the internal voltage-to-current amplifier. Connect the VADJ

pin to the REF pin for a 1.5A output current. For lower

output currents, program the VADJ pin using the following

formula: ILED = 1.5A • VADJ/1.25V.

PWM1, PWM2 (Pins 20, 11): The PWM pin controls the

connection of the VC pin to the internal circuitry. When

the PWM pin is low, the VC pin is disconnected from the

internal circuitry and draws minimal current. If the PWM

feature is unused, leave this pin unconnected.

BLOCK DIAGRAM

VIN

CIN

VIN

SHDN

RT

RT

VIN

D1

BOOST1

INT REG

AND

UVLO

MASTER

OSC

BOOST2

D2

C1

Q1

L1

SW1

DRIVER

D3

OUT1

COUT1

LED1

0.067Ω 100Ω

C1

QR

QS

DLED1

PWM 1

VC1

CC1

gm1

Q3

1.25k

∑ SLOPE COMP

MOSC 1

SLAVE

OSC

SLOPE COMP ∑

MOSC 2

SLAVE

OSC

FREQUENCY

FOLDBACK

FREQUENCY

FOLDBACK

–

+

2V

2V

1.25V

C2

RQ

SQ

C2

Q2

SW2

L2

DRIVER

D4

100Ω

0.067Ω

OUT2

LED2

COUT2

gm2

Q4

1.25k

DLED 2

PWM2

VC2

CC2

VADJ1

REF

VADJ2 EXPOSED

GND

PAD

3475 BD

3475fb

6

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