LT3599(RevD) Просмотр технического описания (PDF) - Linear Technology

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LT3599
(Rev.:RevD)

4-Channel 120mA LED Driver with ±1.5% Current Matching

Linear Technology 

LT3599

Pin Functions

CTRL: LED Current Control. If the CTRL pin is not used,

tie this pin to VREF.

DISABLE4: Allows Disabling Channel 4. Connect to VREF

to disable channel 4. If channel 4 is disabled, the LED4 pin

should be connected to the LED3 pin. Connect DISABLE4

to ground to allow operation of channel 4.

Exposed Pad: Ground. The ground for the IC should be

soldered to a continuous copper ground plane under the

LT3599 die.

FB: Feedback Pin for Overvoltage Protection. Reference

voltage is 1.223V. Connect the resistive divider tap here.

Minimize trace area at FB. Set VOUT according to VOUT =

1.223(1 + R2/R1) when overvoltage protection occurs.

GND: Analog Ground. Tie directly to local ground plane.

Connect RT, ISET and TSET resistors between this local

ground plane and their respective pins.

ISET: Programs Led Current for Each String. A resistor

to ground programs LED currents between 30mA and

120mA.

LED1-4: LED String Output. Connect the bottom cathode

of each LED string to these pins.

OPENLED: Open LED Flag. An open-collector output when

any LED string opens.

NC: No Connect Pins. Can be left open or connected to

any ground plane.

PWM: 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: A Resistor to Ground Which Programs Switching

Frequency Between 200kHz and 2.1MHz. For SYNC func-

tion, choose the resistor to program a frequency 20%

slower than the SYNC pulse frequency. Do not leave this

pin open.

SHDN/UVLO: The SHDN/UVLO pin has an accurate 1.36V

threshold and can be used to program an undervoltage

lockout (UVLO) threshold for system input supply using a

resistor divider from supply to ground. A 4µA pin current

hysteresis allows programming of undervoltage lockout

(UVLO) hysteresis. 1.36V turns the part on and removes a

4µA sink current from the pin. SHDN/UVLO = 0V reduces

VIN current < 0.1µA. SHDN/UVLO can be directly connected

to VIN. Do not leave this pin open.

SHORTLED: Indicates a high side short (LED pin shorted

to VOUT). This is an open-collector output.

SS: Soft-Start Pin. Place a soft-start capacitor here. Upon

start-up, a 11µA current charges the capacitor. Use a larger

capacitor for a slower start-up.

SW: Switch Pin. This is the collector of the internal NPN

power switch. Minimize the metal trace area connected

to this pin to minimize EMI.

SYNC: 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.

TSET: Programs LT3599 junction temperature breakpoint,

beyond which LED currents will begin to decrease. An

internal VPTAT threshold (see Block Diagram) increases

with junction temperature. When VPTAT exceeds TSET pin

voltage, LED currents are decreased. If the function is not

required, connect TSET pin to VREF pin. If the TSET pin is

not used, tie this pin to VREF.

VC: Error Amplifier Output Pin. Tie the external compensa-

tion network to this pin.

VIN : Input Supply Pin. Must be locally bypassed with a

capacitor to ground.

VO_SW: Drain of an Internal PMOS. The internal PMOS

disconnects the feedback resistors from the VOUT pin

during shutdown and when the PWM pin is low.

VOUT: Output Pin. This pin provides power to all LEDs.

VREF : Bandgap Voltage Reference. Internally set to 1.227V.

This pin can supply up to 100µA. Can be used to program

the CTRL pin voltage using resistor dividers to ground.

3599fd



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