LTC3814-5_15 Datasheet, PDF (8/30 Pages) Linear Technology – 60V Current Mode Synchronous Step-Up Controller

LTC3814-5
PIN FUNCTIONS
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 Amplifier 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 floating drive to the top MOSFET.
BOOST (Pin 16): Top Gate Driver Supply. The BOOST pin
supplies power to the floating 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 floating charge-
pumped supply at BOOST.
GND (Exposed Pad Pin 17): Ground. The Exposed Pad
must be soldered to PCB ground.
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