Datasheet

LTC3827-1
8
38271fe
PIN FUNCTIONS
I
TH1,
I
TH2
(Pins 1, 13): Error Amplifi er Outputs and Switch-
ing Regulator Compensation Points. Each associa-ted
channel’s current comparator trip point increases with
this control voltage.
V
FB1
, V
FB2
(Pins 2, 12): Receives the remotely sensed
feedback voltage for each controller from an external
resistive divider across the output.
SENSE1
+
, SENSE2
+
(Pins 3, 11): 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 4, 10): The (–) Input to the
Differential Current Comparators.
PLLLPF (Pin 5): The phase-locked loop’s lowpass fi lter is
tied to this pin when synchronizing to an external clock.
Alternatively, tie this pin to GND, INTV
CC
or leave fl oating to
select 250kHz, 530kHz or 400kHz switching frequency.
PLLIN/MODE (Pin 6): External Synchronization Input to
Phase Detector and Forced Continuous Control Input. When
an external clock is applied to this pin, the phase-locked
loop will force the rising TG1 signal to be synchronized
with the rising edge of the external clock. In this case, an
R-C fi lter must be connected to the PLLLPF pin. When
not synchronizing to an external clock, this input, which
acts on both controllers, determines how the LTC3827-1
operates at light loads. Pulling this pin below 0.7V selects
Burst Mode operation. Tying this pin to INTV
CC
forces
continuous inductor current operation. Tying this pin to
a voltage greater than 0.9V and less than INTV
CC
–1.2 V
selects pulse-skipping operation.
SGND (Pin 7): Small-Signal Ground common to both
controllers, must be routed separately from high cur-
rent grounds to the common (–) terminals of the
C
IN
capacitors.
RUN1, RUN2 (Pins 8, 9): Digital Run Control Inputs for
Each Controller. Forcing either of these pins below 0.7V
shuts down that controller. Forcing both of these pins
below 0.7V shuts down the entire LTC3827-1, reducing
quiescent current to approximately 8µA.
INTV
CC
(Pin 19): Output of the Internal Linear Low Dropout
Regulator. The driver and 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
CC
(Pin 20): External Power Input to an Internal LDO
Connected to INTV
CC
. This LDO supplies INTV
CC
power,
bypassing the internal
LDO powered from V
IN
whenever
EXTV
CC
is higher than 4.7V. See EXTV
CC
Connection in
the Applications Information section. Do not exceed 10V
on this pin.
PGND (Pin 21): 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
.
V
IN
(Pin 22): Main Supply Pin. A bypass capacitor should
be tied between this pin and the signal ground pin.
BG1, BG2 (Pins 23, 18): High Current Gate Drives for Bot-
tom (Synchronous) N-Channel MOSFETs. Voltage swing
at these pins is from ground to INTV
CC
.
BOOST1, BOOST2 (Pins 24, 17): Bootstrapped Supplies
to the Topside Floating Drivers. Capacitors are connected
between the BOOST and SW 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 25, 16): 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 26, 15): High Current Gate Drives for Top
N-Channel MOSFETs. These are the outputs of fl oating
drivers with a voltage swing equal to INTV
CC
– 0.5V su-
perimposed on the switch node voltage SW.
PGOOD1 (Pin 27): Open-Drain Logic Output. PGOOD1 is
pulled to ground when the voltage on the V
FB1
pin is not
within ±10% of its set point.
TRACK/SS1, TRACK/SS2 (Pins 28, 14): External Track-
ing and Soft-Start Input. The LTC3827-1 regulates the
V
FB1,2
voltage to the smaller of 0.8V or the voltage on the
TRACK/SS1,2 pin. A internal 1µA pull-up current source
is connected to this pin. A capacitor to ground at this
pin sets the ramp time to fi nal regulated output voltage.
Alternatively, a resistor divider on another voltage supply
connected to this pin allows the LTC3827-1 output to track
the other supply during startup.