LTC3814-5
8
38145fc
I
OFF
(Pin 1): Off-Time Current Input. Tie a resistor from
V
OUT
to this pin to set the one-shot timer current and
thereby set the switching frequency.
V
OFF
(Pin 2): Off-Time Voltage Input. Voltage trip point
for the on-time comparator. Tying this pin to an external
resistive divider from the input makes the off-time pro-
portional to V
IN
. The comparator defaults to 0.7V when
the pin is grounded and defaults to 2.4V when the pin is
connected to INTV
CC
.
V
RNG
(Pin 3): Sense Voltage Limit Set. The voltage at this
pin sets the nominal sense voltage at maximum output
current and can be set from 0.5V to 2V by a resistive
divider from INTV
CC
. The nominal sense voltage defaults
to 95mV when this pin is tied to ground, and 215mV when
tied to INTV
CC
.
PGOOD (Pin 4): Power Good Output. Open-drain logic
output that is pulled to ground when the output voltage
is not between ±10% of the regulation point. The output
voltage must be out of regulation for at least 125µs before
the power good output is pulled to ground.
I
TH
(Pin 5): Error Amplifi er Compensation Point and Cur-
rent Control Threshold. The current comparator threshold
increases with control voltage. The voltage ranges from
0V to 2.6V with 1.2V corresponding to zero sense voltage
(zero current).
V
FB
(Pin 6): Feedback Input. Connect V
FB
through a resistor
divider network to V
OUT
to set the output voltage.
RUN/SS (Pin 7): RUN/Soft-Start Input. For soft-start, a
capacitor to ground at this pin sets the ramp rate of the
maximum current sense threshold. Pulling this pin below
0.9V will shut down the LTC3814-5, turn off both of the
external MOSFET switches and reduce the quiescent sup-
ply current to 224µA.
SGND (Pin 8): Signal Ground. All small-signal components
should connect to this ground and eventually connect to
PGND at one point.
NDRV (Pin 9): Drive Output for External Pass Device of
the Linear Regulator for INTV
CC
. Connect to the gate of an
external NMOS pass device and a pull-up resistor to the
input voltage V
IN
or the output voltage V
OUT
.
EXTV
CC
(Pin 10): External Driver Supply Voltage. When
this voltage exceeds 4.7V, an internal switch connects
this pin to INTV
CC
through an LDO and turns off the exter-
nal MOSFET connected to NDRV, so that controller and
gate drive are drawn from EXTV
CC
.
INTV
CC
(Pin 11): Main Supply and Driver Supply Pin. All
internal circuits and bottom gate output driver are powered
from this pin. INTV
CC
should be bypassed to SGND and
PGND with a low ESR (X5R or better) 1µF capacitor in
close proximity to the LTC3814-5.
BG (Pin 12): Bottom Gate Drive. The BG pin drives the
gate of the bottom N-channel main switch MOSFET. This
pin swings from PGND to INTV
CC
.
PGND (Pin 13): Bottom Gate Return. This pin connects
to the source of the pull-down MOSFET in the BG driver
and is normally connected to ground.
SW (Pin 14): Switch Node Connection to Inductor and
Bootstrap Capacitor. Voltage swing at this pin is from a
Schottky diode (external) voltage drop below ground
to V
OUT
.
TG (Pin 15): Top Gate Drive. The TG pin drives the gate of
the top N-channel synchronous switch MOSFET. The TG
driver draws power from the BOOST pin and returns to the
SW pin, providing true fl oating drive to the top MOSFET.
BOOST (Pin 16): Top Gate Driver Supply. The BOOST pin
supplies power to the fl oating TG driver. BOOST should
be bypassed to SW with a low ESR (X5R or better) 0.1µF
capacitor. An additional fast recovery diode from INTV
CC
to the BOOST pin will create a complete fl oating charge-
pumped supply at BOOST.
GND (Exposed Pad Pin 17): Ground. The Exposed Pad
must be soldered to PCB ground.
PIN FUNCTIONS
