LT3755 datasheet(11/30 Pages) LINEAR

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LT3922

3922f

For more information www.linear.com/LT3922

pin FuncTions

FAULT: Fault Pin. Connect to INTVCC through a resistance

of 100k. An internal switch pulls this pin low when any of

following conditions happen:

1. Open LED: VFB > 1.14V and (VISP – VISN) < 10mV

2. Shorted LED:

(VISP – VISN) > 150mV for more than 300us, or

(VISP – VISN) > 0.7V, or

VOUT < (VIN – 2V)

RT: Timing Resistor Pin. A resistor from this pin to GND

programs the switching frequency between 200kHz and

2MHz. Do not leave this pin open.

SYNC/SPRD: Synchronization Pin. To override the pro-

grammed switching frequency, drive this pin with an

external clock having a frequency between 200kHz and

2MHz. Even when using the external clock, select an RT

resistor that corresponds to the desired switching fre-

quency. Tie the pin to INTVCC to enable Spread Spectrum

Frequency Modulation. This pin should be tied to GND

when not in use.

RP: PWM Resistor Pin. Connect a resistor from this pin to

GNDtosetthefrequencyoftheinternalPWMsignal.Donot

use a resistor larger than 1MΩ. If using an external PWM

pulse for LED dimming, tie this pin to GND. Refer to the

Application Information section for a detailed explanation.

PWM: PWM Input Pin. With the RP pin tied to GND, drive

this pin with a digital pulse to control PWM dimming of

the LEDs. Alternatively, when using a resistor on the RP

pin to GND, set the voltage of this pin between 1V and

2V to generate an internal pulse with duty cycle between

0% and 100%. When using an analog signal, place a 1µF

bypass capacitor between this pin and GND. Tie this pin

high when PWM dimming is not required.

PWMTG: PWM Driver Output Pin. This pin can drive the

gate of an external high-side PMOS device for PWM dim-

ming of LEDs. Do not force any voltage on this pin.

VOUT: Output Pins. Connect to the output and place output

capacitors between these pins and GND as close as pos-

sible to the package. Refer to the Application Information

section for the recommended capacitor placements.

GND (Pin 22, 23, 25, Exposed Pad Pin 29): Ground Pins.

All GND pins must be soldered to the board ground plane.

NC: No Connect Pins. These pins can be left open or con-

nected to the ground.

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