8
LTC1628/LTC1628-PG
1628fb
RUN/SS1, RUN/SS2: 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
is also invoked via this pin as described in the Applications
Information section.
SENSE1
+
, SENSE2
+
: The (+) Input to the Differential
Current Comparators. The I
th
pin voltage and controlled
offsets between the SENSE
–
and SENSE
+
pins in conjunc-
tion with R
SENSE
set the current trip threshold.
SENSE1
–
, SENSE2
–
: The (–) Input to the Differential
Current Comparators.
V
OSENSE1
, V
OSENSE2
: Receives the remotely-sensed feed-
back voltage for each controller from an external resistive
divider across the output.
FREQSET: 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: Control pin that determines which circuitry re-
mains active when the controllers are shut down and/or
provides a common control point to shut down both con-
trollers. See the Operation section for details.
FCB: Forced Continuous Control Input. This input acts on
the first controller (or both controllers depending upon
the FLTCPL pin—see pin description), and is
normally used to regulate a secondary winding. Pulling
this pin below 0.8V will force continuous synchronous
operation for the first and optionally the second control-
ler. Do not leave this pin floating.
I
TH1,
I
TH2
: Error Amplifier Output and Switching Regulator
Compensation Point. Each associated channels’ current
comparator trip point increases with this control voltage.
SGND: Small Signal Ground common to both con-
trollers, must be routed separately from high current
grounds to the common (–) terminals of the C
OUT
capacitors.
3.3V
OUT
: Output of a linear regulator capable of supplying
10mA DC with peak currents as high as 50mA.
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
IN
.
INTV
CC
: 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 4.7µF tanta-
lum or other low ESR capacitor. The INTV
CC
regulator
standby function is determined by the STBYMD pin.
EXTV
CC
: External Power Input to an Internal Switch Con-
nected 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: High Current Gate Drives for Bottom (Synchro-
nous) N-Channel MOSFETs. Voltage swing at these pins is
from ground to INTV
CC
.
V
IN
: Main Supply Pin. A bypass capacitor should be tied
between this pin and the signal ground pin.
BOOST1, BOOST2: 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
CC
pins. Voltage swing at the
boost pins is from INTV
CC
to (V
IN
+ INTV
CC
).
SW1, SW2: Switch Node Connections to Inductors. Volt-
age swing at these pins is from a Schottky diode (external)
voltage drop below ground to V
IN
.
TG1, TG2: High Current Gate Drives for Top N-Channel
MOSFETs. These are the outputs of floating drivers with a
voltage swing equal to INTV
CC
– 0.5V superimposed on
the switch node voltage SW.
FLTCPL: (LTC1628 Only) Fault Coupling Control Pin that
determines if fault/normal conditions on one controller
will act on the other controller. FLTCPL = INTV
CC
to couple
channels; FLTCPL = 0V to decouple.
UU
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PI FU CTIO S
