LTC3868-1
9
38681fd
PIN FUNCTIONS
(QFN/SSOP)
INTV
CC
(Pin 17/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 ceramic or other
low ESR capacitor. Do not use the INTV
CC
pin for any
other purpose.
EXTV
CC
(Pin 18/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 14V on this pin.
PGND (Pin 19/Pin 21): Driver Power Ground. Connects to
the sources of bottom (synchronous) N-channel MOSFETs
and the (–) terminal(s) of C
IN
.
V
IN
(Pin 20/Pin 22): Main Supply Pin. A bypass capaci-
tor should be tied between this pin and the signal ground
pin.
BG1, BG2 (Pin 21, Pin 16/Pin 23, Pin 18): High Current
Gate Drives for Bottom (Synchronous) N-Channel
MOSFETs. Voltage swing at these pins is from ground
to INTV
CC
.
BOOST1, BOOST2 (Pin 22, Pin 15/Pin 24, Pin 17): Boot-
strapped 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 (Pin 23, Pin 14/Pin 25, Pin 16): Switch Node
Connections to Inductors.
TG1, TG2 (Pin 24, Pin 13/Pin 26, Pin 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 superimposed on the switch node voltage
SW.
PGOOD1 (Pin 25/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.
SS1, SS2 (Pin 26, Pin 12/Pin 28, Pin 14): External Soft-
Start Input. The LTC3868-1 regulates the V
FB1,2
voltage
to the smaller of 0.8V or the voltage on the SS1,2 pin. An
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. This pin is also used as
the short-circuit latchoff timer.
I
TH1
, I
TH2
(Pin 27, Pin 11/Pin 1, Pin 13): Error Amplifi er
Outputs and Switching Regulator Compensation Points.
Each associated channel’s current comparator trip point
increases with this control voltage.
V
FB1
, V
FB2
(Pin 28, Pin 10/Pin 2, Pin 12): Receives the
remotely sensed feedback voltage for each controller from
an external resistive divider across the output.
SENSE1
+
, SENSE2
+
(Pin 1, Pin 9/Pin 3, Pin 11): The (+)
input to the differential current comparators are normally
connected to DCR sensing networks or current sensing
resistors. The I
TH
pin voltage and controlled offsets between
the SENSE
–
and SENSE
+
pins in conjunction with R
SENSE
set the current trip threshold.
