LT3598 Просмотр технического описания (PDF) - Linear Technology

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LT3598

6-String 30mA LED Driver with ±1.5% Current Matching

Linear Technology 

LT3598

PIN FUNCTIONS (QFN/TSSOP)

LED1-6 (Pins 1, 2, 3, 4, 5, 6/Pins 4, 5, 6, 7, 8, 9): LED

String Output. Connect the bottom cathode of each LED string

to these pins. Tie pins to VOUT if the string is not used.

OPENLED (Pin 7/Pin 10): Open LED Flag When Any LED

String Opens. The output is open-collector. Tie a resistor

to other supply for open LED flag function.

ISET (Pin 8/Pin 11): Programs LED Current for Each String.

Connect a 14.7k resistor between ISET and GND to program

each LED string current to 20mA. A 47pF capacitor on the

ISET pin reduces current ripple in each LED string.

CTRL (Pin 9/Pin 12): LED Current Control. If the CTRL

pin is not used, tie this pin to VREF through a 10k to 20k

resistor.

VC (Pin 10/Pin 13): Error Amplifier Output Pin. Tie the

external compensation network to this pin.

FB (Pin 11/Pin 14): Feedback Pin for Overvoltage

Protection. Reference voltage is 1.230V. Connect the

resistive divider tap here. Minimize trace area at FB. Set VOUT

according to VOUT = 1.230(1 + R2/R1) when overvoltage

protection occurs (see Figure 2).

TSET (Pin 12/Pin 15): An external resistor divider from

VREF programs a decrease in LED current versus internal

junction temperature (setting temperature breakpoint and

slope). If the TSET pin is not used, tie this pin to VREF.

NC (Pin 13/Pin 16): No Connection.

SYNC (Pin 14/Pin 17): Frequency Synchronization Pin.

This input allows for synchronizing the operating frequency

to an external clock. The RT resistor should be chosen to

program a switching frequency 20% slower than SYNC

pulse frequency. This pin should be grounded if this

feature is not used.

PWM (Pin 15/Pin 18): Input Pin for PWM Dimming Control.

Above 1V allows converter switching and below 0.4V

disables switching with VC pin level maintained. A PWM

signal driving the PWM pin provides accurate dimming

control. The PWM signal can be driven from 0V to 5V. If

unused, the pin should be connected to VREF.

RT (Pin 16/Pin 19): A resistor to ground programs

switching frequency between 200kHz and 2.5MHz. For

SYNC function, choose the resistor to program a frequency

20% slower than the SYNC pulse frequency. Do not leave

this pin open.

SS (Pin 17/Pin 20): Soft-Start Pin. Place a soft-start

capacitor here. Upon start-up, a 10μA current charges

the capacitor. Use a larger capacitor for slower start-up.

Leave open if not used.

VREF (Pin 18/Pin 21): Bandgap Voltage Reference.

Internally set to 1.230V. This pin can supply up to 100μA.

Can be used to program the CTRL pin voltage using resistor

dividers to ground.

GND (Pin 19/Pin 22): Ground. Tie directly to local ground

plane.

SHDN (Pin 20/ Pin 23): Shutdown Pin. Tie to 1.6V or more

to enable the device. Tie below 0.4V or less to disable

device. Do not float this pin.

VIN (Pin 21/Pin 24): Input Supply Pin. Must be locally

bypassed with a capacitor to ground.

SW (Pin 22/Pin 1): Switch Pin. This is the collector of the

internal NPN power switch. Minimize the metal trace area

connected to this pin to minimize EMI.

VOUT (Pin 23/ Pin 2): Output Pin. This pin provides power

to all LEDs.

VO_SW (Pin 24/ Pin 3): Drain of an Internal PMOS. The

internal PMOS disconnects the feedback resistors from

the VOUT pin during shutdown and the PWM transitioned

to low.

Exposed Pad (Pin 25/ Pin 25): Ground. The Exposed Pad

must be soldered to the PCB.

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