LTC3858-2
9
38582f
PIN FUNCTIONS
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 ceramic or other low ESR ca-
pacitor. Do not use the INTV
CC
pin for any other purpose.
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 14V
on this pin.
PGND (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 22): Main Input Supply Pin. A bypass capacitor
should be tied between this pin and the signal ground pin.
BG1, BG2 (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 24, Pin 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 (Pin 25, Pin 16): Switch Node Connections
to Inductors.
TG1, TG2 (Pin 26, Pin 15): High Current Gate Drives for
Top N-Channel MOSFETs. These are the outputs of float-
ing drivers with a voltage swing equal to INTV
CC
– 0.5V
superimposed on the switch node voltage SW.
PGOOD1, PGOOD2 (Pin 27, Pin 14): Open-Drain Logic
Output. PGOOD1,2 is pulled to ground when the voltage
on the V
FB1,2
pin is not within ±10% of its set point.
SS1, SS2 (Pin 29, Pin 13): External Soft-Start Input. The
LTC3858-2 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 final regulated
output voltage. Alternatively, a resistor divider on another
voltage supply connected to this pin allows the LTC3858-2
output to track the other supply during start-up.
I
TH1
, I
TH2
(Pin 30, Pin 12): Error Amplifier Outputs and
Switching Regulator Compensation Points. Each associ-
ated channel’s current comparator trip point increases
with this control voltage.
V
FB1
, V
FB2
(Pin 31, Pin 11): Receives the remotely sensed
feedback voltage for each controller from an external
resistive divider across the output.
SENSE1
+
, SENSE2
+
(Pin 32, Pin 10): The (+) Input to
the differential current comparators that are normally
connected to inductor 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.
