LT8697
9
8697fb
For more information www.linear.com/LT8697
PIN FUNCTIONS
SYNC (Pin 1): External Clock Synchronization Input.
Tie to a clock source for synchronization to an external
frequency and forced continuous mode. Tie to INTV
CC
if
not used. Do not float.
TR/SS (Pin 2): Output Tracking and Soft-Start Pin. This
pin allows user control of output voltage ramp rate during
start-up. A TR/SS voltage below 0.97V forces the LT8697
to regulate V
USB5V
to 5 times the TR/SS voltage. When
TR/SS is above 0.97V, the tracking function is disabled
and the internal reference resumes control of the error
amplifier. An internal 2.2µA pull-up current from INTV
CC
on this pin allows a capacitor to program output voltage
slew rate. This pin is pulled to ground when EN/UV is low,
during thermal shutdown and when V
IN
below its under-
voltage lockout threshold; use a series resistor of at least
10k if driving from a low impedance output.
RT (Pin 3): Tie a resistor between RT and ground to set
the switching frequency.
EN/UV (Pin 4): The LT8697 is shut down when this pin
is low and active when this pin is high. The hysteretic
threshold voltage is 1.00V going up and
0.96V when going
down. Ti
e to V
IN
if the shutdown feature is not used. An
external resistor divider from V
IN
can be used to program
a V
IN
threshold below which the LT8697 will shut down.
V
IN
(Pins 5, 6): The V
IN
pins supply current to the LT8697
internal circuitry and to the internal topside power switch.
These pins must be tied together and be locally bypassed.
Place the positive terminal of the input capacitor as close
as possible to the V
IN
pins, and the negative terminal as
close as possible to the PGND pins.
PGND (Pins 7, 8): Power Switch Ground. These pins are
the return path of the internal bottom side power switch
and must be tied together. Place the negative terminal of
the input capacitor as close as possible to the PGND pins.
NC (Pins 9-12): No Connect. These pins are floating and
are not connected to the LT8697. Tie these pins to the
same copper as the exposed pad. See Figure 8.
SW (Pins 13, 14, 15): The SW pins are the outputs of the
internal power switches. Tie these pins together and con
-
nect them
to the inductor and boost capacitor. This node
should
be kept small on the PCB for good performance.
Do not drive these pins above V
IN
.
BST (Pin 16): This pin is used to provide a drive voltage,
higher than the input voltage, to the topside power switch.
Place a 0.1µF boost capacitor between this pin and SW as
close as possible to the LT8697 IC.
INTV
CC
(Pin 17): Internal 3.4V Regulator Bypass Pin. The
internal power drivers and control circuits are powered
from this voltage. The INTV
CC
maximum output current
is 20mA. INTV
CC
current will be supplied from SYS if
V
SYS
> 3.1V, otherwise current will be drawn from V
IN
.
Decouple this pin to power ground with at least a 1µF low
ESR ceramic capacitor. Do not load the INTV
CC
pin with
external circuitry.
SYS (Pin 18): The internal regulator will draw current
from SYS instead of V
IN
when SYS is tied to a voltage
higher than 3.3V. The SYS pin must be tied to the side of
the inductor opposite the SW pin and must be bypassed
by the output capacitor. SYS is also the secondary input
to the error amp and regulates to a maximum of 5.8V.
