LTC3728 Linear Technology, LTC3728 Datasheet - Page 8

• Manufacturer Part Number: LTC3728
• Description: 2-Phase Synchronous Step-Down Switching Regulator
• Manufacturer: Linear Technology

LTC3728
PI FU CTIO S
RUN/SS1, RUN/SS2 (Pins 1, 15/Pins 28, 13): Combina-
tion of soft-start, run control inputs and short-circuit detec-
tion 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 is also invoked via this pin as de-
scribed in the Applications Information section.
SENSE1
to the Differential Current Comparators. The I
and controlled offsets between the SENSE
pins in conjunction with R
old.
SENSE1
to the Differential Current Comparators.
V
remotely-sensed feedback voltage for each controller from
an external resistive divider across the output.
PLLFLTR (Pin 5/Pin 2): The Phase-Locked Loop’s Low-
pass Filter is Tied to This Pin. Alternatively, this pin can be
driven with an AC or DC voltage source to vary the fre-
quency of the internal oscillator.
PLLIN (Pin 6/Pin 3): External Synchronization Input to Phase
Detector. This pin is internally terminated to SGND with
50kΩ. 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 (Pin 7/Pin 4): 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
Switching Regulator Compensation Point. Each associated
channels’ current comparator trip point increases with this
control voltage.
SGND (Pin 9/Pin 6): Small Signal Ground common to
both controllers, must be routed separately from high
current grounds to the common (–) terminals of the
C
3.3V
of supplying 10mA DC with peak currents as high as 50mA.
8
TH1,
OSENSE1
OUT
U
OUT
I
TH2
capacitors.
+
–
(Pin 10/Pin 7): Output of a linear regulator capable
, SENSE2
, SENSE2
, V
(Pins 8, 11/Pins 5, 8): Error Amplifier Output and
U
OSENSE2
+
–
U
(Pins 2, 14/Pins 30, 12): The (+) Input
(Pins 3, 13/Pins 31, 11): The (–) Input
(Pins 4, 12/Pins 1, 9): Receives the
SENSE
G Package/UH Package
set the current trip thresh-
–
th
and SENSE
pin voltage
+
NC (Pins 10, 16, 29, 32 UH Package Only): No Connect.
PGND (Pin 20/Pin 19): Driver Power Ground. Connects to the
sources of bottom (synchronous) N-channel MOSFETs, an-
odes of the Schottky rectifiers and the (–) terminal(s) of C
INTV
Dropout Regulator and the EXTV
control circuits are powered from this voltage source. Must
be decoupled to power ground with a minimum of 4.7µF
tantalum or other low ESR capacitor.
EXTV
Internal Switch Connected to INTV
and supplies V
out regulator, whenever EXTV
EXTV
7V on this pin.
BG1, BG2 (Pins 23, 19/Pins 22, 18): High Current Gate
Drives for Bottom (Synchronous) N-Channel MOSFETs.
Voltage swing at these pins is from ground to INTV
V
should be tied between this pin and the signal ground pin.
BOOST1, BOOST2 (Pins 25, 18/Pins 24, 17): Bootstrapped
Supplies to the Top Side Floating Drivers. Capacitors are
connected between the boost and switch pins and Schot-
tky diodes are tied between the boost and INTV
Voltage swing at the boost pins is from INTV
INTV
SW1, SW2 (Pins 26, 17/Pins 25, 15): Switch Node
Connections to Inductors. Voltage swing at these pins is
from a Schottky diode (external) voltage drop below
ground to V
TG1, TG2 (Pins 27, 16/Pins 26, 14): High Current Gate
Drives for Top N-Channel MOSFETs. These are the outputs
of floating drivers with a voltage swing equal to INTV
0.5V superimposed on the switch node voltage SW.
PGOOD (Pin 28/Pin 27): Open-Drain Logic Output. PGOOD
is pulled to ground when the voltage on either V
is not within ±7.5% of its set point.
Exposed Pad (Pin 33) SGND: The exposed pad must be
soldered to PCB ground for elecrical contact and rated
thermal performance.
IN
(Pin 24/Pin 23): Main Supply Pin. A bypass capacitor
CC
CC
CC
CC
).
(Pin 21/Pin 20): Output of the Internal 5V Linear Low
connection in Applications section. Do not exceed
(Pin 22/Pin 21): External Power Input to an
IN
.
CC
power, bypassing the internal low drop-
CC
CC
www.DataSheet4U.com
is higher than 4.7V. See
CC
Switch. The driver and
. This switch closes
CC
OSENSE
to (V
CC
CC
pins.
3728fb
CC
IN
pin
.
IN
+
–
.