LTC3858-1 Linear Technology Corporation, LTC3858-1 Datasheet - Page 9

• Manufacturer Part Number: LTC3858-1
• Description: Dual 2-Phase Synchronous Step-Down Controller
• Manufacturer: Linear Technology Corporation

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INTV
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
other purpose.
EXTV
Internal LDO Connected to INTV
INTV
V
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
V
capacitor should be tied between this pin and the signal
ground pin.
BG1, BG2 (Pins 21, 23/Pins 16, 18): High Current Gate
Drives for Bottom (Synchronous) N-Channel MOSFETs.
Voltage swing at these pins is from ground to INTV
BOOST1, BOOST2 (Pins 22,24/Pins 15, 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
pins. Voltage swing at the BOOST pins is from INTV
(V
SW1, SW2 (Pins 23, 25/Pins 14, 16): Switch Node Con-
nections to Inductors.
PIN FUNCTIONS
IN
IN
IN
whenever EXTV
(Pin 20/Pin 22): Main Input Supply Pin. A bypass
+ INTV
CC
CC
CC
(Pin 17/Pin 19): Output of the Internal Linear Low
power, bypassing the internal LDO powered from
(Pin 18/Pin 20): External Power Input to an
CC
).
CC
is higher than 4.7V. See EXTV
(QFN/SSOP)
IN
.
CC
. This LDO supplies
CC
pin for any
CC
CC
.
CC
CC
to
TG1, TG2 (Pins 24, 26/Pins 13, 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
– 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
pin is not within ±10% of its set point.
SS1, SS2 (Pins 26, 28/Pins 12, 14): External Soft-Start
Input. The LTC3858-1 regulates the V
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
and Switching Regulator Compensation Points. Each as-
sociated channel’s current comparator trip point increases
with this control voltage.
V
sensed feedback voltage for each controller from an external
resistive divider across the output.
SENSE1
to the differential current comparators that are normally
connected to inductor DCR sensing networks or current
sensing resistors. The I
between the SENSE
R
Exposed Pad (Pin 29/NA): SGND. Must be soldered to
the PCB.
TH1
FB1
SENSE
, I
, V
TH2
FB2
set the current trip threshold.
+
, SENSE2
(Pins 27, 1/Pins 11, 13): Error Amplifi er Outputs
(Pins 28, 2/Pins 10, 12): Receives the remotely
+
–
(Pins 1, 3/Pins 9, 11): The (+) input
and SENSE
TH
pin voltage and controlled offsets
+
pins in conjunction with
LTC3858-1
FB1,2
voltage to
38581f
9
FB1
CC