B0530W データシートの表示（PDF） - Linear Technology

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B0530W

Step-Down 1A LED Driver

Linear Technology 

LT3474/LT3474-1

PIN FUNCTIONS

DNC (Pins 1, 16): Do not connect external circuitry to these

pins, or tie them to GND. Leave the DNC pins floating.

OUT (Pin 2): The OUT pin is the input to the current sense

resistor. Connect this pin to the inductor and the output

capacitor.

LED (Pin 3): The LED pin is the output of the current sense

resistor. Connect the anode of the LED here.

VIN (Pin 4): The VIN pin supplies current to the internal

circuitry and to the internal power switch and must be

locally bypassed.

SW (Pin 5): The SW pin is the output of the internal power

switch. Connect this pin to the inductor and switching

diode.

BOOST (Pin 6): The BOOST pin is used to provide a drive

voltage, higher than the input voltage, to the internal bipolar

NPN power switch.

BIAS (Pin 7): The BIAS pin connects through a Schottky

diode to BOOST. Tie to OUT.

GND (Pins 8, 15, Exposed Pad Pin 17): Ground. Tie both

GND pins and the Exposed Pad directly to the ground

plane. The Exposed Pad metal of the package provides both

electrical contact to ground and good thermal contact to

the printed circuit board. It must be soldered to the circuit

board for proper operation.

RT (Pin 9): The RT pin is used to set the internal oscilla-

tor frequency. Tie an 80.6k resistor from RT to GND for a

500kHz switching frequency.

SHDN (Pin 10): 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

under-voltage lockout. Pull below 0.3V to shut down the

LT3474/LT3474-1. Pull above 2.65V to enable the LT3474/

LT3474-1. Tie to VIN if the SHDN function is unused.

REF (Pin 11): The REF pin is the buffered output of the

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

a 1A output current, or use a resistor divider to generate a

lower voltage at the VADJ pin. Leave this pin unconnected

if unused.

VC (Pin 12): 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.

VADJ (Pin 13): The VADJ pin is the input to the internal

voltage to current amplifier. Connect the VADJ pin to the

REF pin for a 1A output current. For lower output cur-

rents, program the VADJ pin using the following formula:

ILED = 1A • VADJ/1.25V.

PWM (Pin 14): 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.

3474fd

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