LT3922
pin FuncTions
FAULT: Fault Pin. Connect to INTV through a resistance
pulse for LED dimming, tie this pin to GND. Refer to the
Application Information section for a detailed explanation.
CC
of 100k. An internal switch pulls this pin low when any of
following conditions happen:
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.
1. Open LED: V > 1.14V and (V – V ) < 10mV
FB
ISP
ISN
2. Shorted LED:
(V – V ) > 150mV for more than 300us, or
ISP
ISN
(V – V ) > 0.7V, or
ISP
OUT
ISN
V
< (V – 2V)
IN
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.
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.
SYNC/SPRD: Synchronization Pin. To override the pro-
grammed switching frequency, drive this pin with an
external clock having a frequency between 200kHz and
V : Output Pins. Connect to the output and place output
OUT
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.
2MHz. Even when using the external clock, select an R
T
resistor that corresponds to the desired switching fre-
quency. Tie the pin to INTV to enable Spread Spectrum
CC
Frequency Modulation. This pin should be tied to GND
GND (Pin 22, 23, 25, Exposed Pad Pin 29): Ground Pins.
All GND pins must be soldered to the board ground plane.
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
NC: No Connect Pins. These pins can be left open or con-
nected to the ground.
3922f
11
For more information www.linear.com/LT3922
Linear Systems [ Linear Systems ]
