LTC3707
8
3707fb
PIN FUNCTIONS
RUN/SS1, RUN/SS2 (Pins 1, 15): Combination of soft-start,
run control 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 is also invoked via this pin as described in the
Applications Information section.
SENSE1
+
, SENSE2
+
(Pins 2, 14): The (+) Input to the
Differential Current Comparators. The I
TH
pin voltage and
controlled offsets between the SENSE
–
and SENSE
+
pins in
conjunction with R
SENSE
set the current trip threshold.
SENSE1
–
, SENSE2
–
(Pins 3, 13): The (–) Input to the
Differential Current Comparators.
V
OSENSE1
, V
OSENSE2
(Pins 4, 12): Receives the remotely-
sensed feedback voltage for each controller from an external
resistive divider across the output.
FREQSET (Pin 5): Frequency Control Input to the Oscillator.
This pin can be left open, tied to ground, tied to INTV
CC
or driven by an external voltage source. This pin can also
be used with an external phase detector to build a true
phase-locked loop.
STBYMD (Pin 6): Control pin that determines which cir-
cuitry remains active when the controllers are shut down
and/or provides a common control point to shut down both
controllers. See the Operation section for details.
FCB (Pin 7): 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 on both controllers.
Do not leave this pin fl oating.
I
TH1,
I
TH2
(Pins 8, 11): Error Amplifi er Output and Switching
Regulator Compensation Point. Each associated channels’
current comparator trip point increases with this control
voltage.
SGND (Pin 9): Small Signal Ground common to both
controllers, must be routed separately from high current
grounds to the common (–) terminals of the C
OUT
capacitors.
3.3V
OUT
(Pin 10): Output of a linear regulator capable
of supplying 10mA DC with peak currents as high as
50mA.
PGND (Pin 20): Driver Power Ground. Connects to the
sources of bottom (synchronous) N-channel MOSFETs,
anodes of the Schottky rectifi ers and the (–) terminal(s)
of C
IN
.
INTV
CC
(Pin 21): Output of the Internal 5V Linear Low
Dropout Regulator and the EXTV
CC
Switch. The driver and
control circuits are powered from this voltage source. Must
be decoupled to power ground with a minimum of 4.7
µ
F
tantalum or other low ESR capacitor. The INTV
CC
regulator
standby function is determined by the STBYMD pin.
EXTV
CC
(Pin 22): External Power Input to an Internal Switch
Connected to INTV
CC
. This switch closes and supplies V
CC
power, bypassing the internal
low dropout regulator, when-
ever EXTV
CC
is higher than 4.7V. See EXTV
CC
connection
in Applications section. Do not exceed 7V on this pin.
BG1, BG2 (Pins 23, 19): High Current Gate Drives for Bot-
tom (Synchronous) N-Channel MOSFETs. Voltage swing
at these pins is from ground to INTV
CC
.
V
IN
(Pin 24): Main Supply Pin. A bypass capacitor should
be tied between this pin and the signal ground pin.
BOOST1, BOOST2 (Pins 25, 18): Bootstrapped Supplies
to the Top Side Floating Drivers. Capacitors are connected
between the boost and switch pins and Schottky diodes are
tied between the boost and INTV
CC
pins. Voltage swing at
the boost pins is from INTV
CC
to (V
IN
+ INTV
CC
).
SW1, SW2 (Pins 26, 17): Switch Node Connections to
Inductors. Voltage swing at these pins is from a Schottky
diode (external) voltage drop below ground to V
IN
.
TG1, TG2 (Pins 27, 16): High Current Gate Drives for
Top N-Channel MOSFETs. These are the outputs of fl oat-
ing drivers with a voltage swing equal to INTV
CC
– 0.5V
superimposed on the switch node voltage SW.
PGOOD (Pin 28): Open-Drain Logic Output. PGOOD is
pulled to ground when the voltage on either V
OSENSE
pin
is not within ±7.5% of its set point.
