Datasheet

LT3514
9
3514fa
For more information www.linear.com/LT3514
RT/SYNC (Pin 17/Pin 17): Set the switching frequency
of the LT3514 by tying an external resistor from this pin
to ground. Select the value of the programming resistor
(R
T
) according to Table 1 in the Applications Information
section. The RT/SYNC pin is also used to synchronize the
internal oscillator of the LT3514 to an external signal. The
synchronization (sync) signal is directly logical compatible
and can be driven by any signal with pulse width greater
than 50ns. The synchronization range is from 350kHz to
2.2MHz.
FB (Pins 19, 20, 21/Pins 18,19, 20): Each feedback pin is
regulated to 800mV. Connect the feedback resistor divider
to this pin. The output voltage is programmed according
to the following equation:
R1= R2 •
V
OUT
0.8V
− 1






where R1 connects between OUT and FB, and R2 connects
between FB and GND. A good value for R2 is 10.2kΩ.
PG (Pin 23/Pin 21): The Power Good pin is the open
collector output of an internal comparator. PG remains
low until all FB pins are greater than 710mV. If not in use,
this pin can be left unconnected. The PG comparator is
disabled in shutdown.
SW5 (Pin 24/Pin 23): The SW5 pin is an open collector
of an internal boost regulator power switch. This power
switch generates the drive voltage 4.85V above the input
voltage (V
IN
), to drive the internal buck regulator power
switches. Connect an inductor from this pin to the V
IN
pin.
SKY (Pin 25/Pin 24): The SKY pin is the output of an in-
tegrated power Schottky diode and is the source of drive
voltage to the internal buck regulator power switches.
Connect a 1
µF capacitor from this pin to the V
IN
pin. Do
not drive this pin with an external voltage source. Do not
draw current from this pin with an external component.
PIN FUNCTIONS
(QFN/TSSOP)