LTC3728LX Linear Technology, LTC3728LX Datasheet - Page 8

• Manufacturer Part Number: LTC3728LX
• Description: 2-Phase Synchronous Regulators
• Manufacturer: Linear Technology

LTC3728L/LTC3728LX
PI FU CTIO S
V
ceives the remotely-sensed feedback voltage for each
controller from an external resistive divider across the
output.
PLLFLTR: Filter Connection for Phase-Locked Loop. Al-
ternatively, this pin can be driven with an AC or DC voltage
source to vary the frequency of the internal oscillator.
PLLIN: External Synchronization Input to Phase Detector.
This pin is internally terminated to SGND with 50k . The
phase-locked loop will force the rising top gate signal of
controller 1 to be synchronized with the rising edge of the
PLLIN signal.
FCB: Forced Continuous Control Input. This input acts on
both controllers and is normally used to regulate a
secondary winding. Pulling this pin below 0.8V will force
continuous synchronous operation.
I
Compensation Point. Each associated channels’ current
comparator trip point increases with this control voltage.
SGND: Small Signal Ground. Common to both con-
trollers, this pin must be routed separately from high
current grounds to the common (–) terminals of the
C
3.3V
10mA DC with peak currents as high as 50mA.
NC: No Connect.
SENSE2
Current Comparators.
SENSE2
Current Comparators. The I
offsets between the SENSE
tion with R
RUN/SS2, RUN/SS1: Combination of soft-start, run con-
trol inputs and short-circuit detection timers. A capacitor
to ground at each of these pins sets the ramp time to full
output current. Forcing either of these pins back below
1.0V causes the IC to shut down the circuitry required for
that particular controller. Latchoff overcurrent protection
8
TH1,
OSENSE1
OUT
U
OUT
I
TH2
capacitors.
: Lnear Regulator Output. Capable of supplying
–
+
: Error Amplifier Output and Switching Regulator
, V
, SENSE1
, SENSE1
U
SENSE
OSENSE2
set the current trip threshold.
+
: Error Amplifier Feedback Input. Re-
–
U
: The (–) Input to the Differential
: The (+) Input to the Differential
–
TH
and SENSE
pin voltage and controlled
+
pins in conjunc-
is also invoked via this pin as described in the Applications
Information section.
TG2, TG1: High Current Gate Drives for Top N-Channel
MOSFETs. These are the outputs of floating drivers with a
voltage swing equal to INTV
the switch node voltage SW.
SW2, SW1: Switch Node Connections to Inductors. Volt-
age swing at these pins is from a Schottky diode (external)
voltage drop below ground to V
BOOST2, BOOST1: Bootstrapped Supplies to the Top Side
Floating Drivers. Capacitors are connected between the
boost and switch pins and Schottky diodes are tied be-
tween the boost and INTV
boost pins is from INTV
BG2, BG1: High Current Gate Drives for Bottom (Synchro-
nous) N-Channel MOSFETs. Voltage swing at these pins is
from ground to INTV
PGND: Driver Power Ground. Connects to the sources of
bottom (synchronous) N-channel MOSFETs, anodes of the
Schottky rectifiers and the (–) terminal(s) of C
INTV
Regulator and the EXTV
circuits are powered from this voltage source. Must be
decoupled to power ground with a minimum of 4.7 F tanta-
lum or other low ESR capacitor.
EXTV
nected to INTV
power, bypassing the internal low dropout regulator, when-
ever EXTV
in Applications section. Do not exceed 7V on this pin.
V
between this pin and the signal ground pin.
PGOOD: Open-Drain Logic Output. PGOOD is pulled to
ground when the voltage on either V
within 7.5% of its set point.
Exposed Pad (UH Package Only): Signal Ground. Must be
soldered to the PCB, providing a local ground for the
control components of the IC, and be tied to the PGND pin
under the IC.
IN
: Main Supply Pin. A bypass capacitor should be tied
CC
CC
: Output of the Internal 5V Linear Low Dropout
: External Power Input to an Internal Switch Con-
CC
is higher than 4.7V. See EXTV
CC
. This switch closes and supplies V
CC
.
CC
CC
Switch. The driver and control
CC
to (V
CC
pins. Voltage swing at the
– 0.5V superimposed on
IN
IN
www.DataSheet4U.com
.
+ INTV
OSENSE
CC
CC
).
IN
connection
.
pin is not
3728lxfa
CC