LTC3868-1 Datasheet, PDF (9/38 Pages) Linear Technology – Low IQ, Dual 2-Phase Synchronous Step-Down Controller

LTC3868-1
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 23/Pin 16, 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 24/Pin 15, 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 23, Pin 25/Pin 14, Pin 16): Switch Node
Connections to Inductors.
TG1, TG2 (Pin 24, Pin 26/Pin 13, Pin 15): 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.
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 28/Pin 12, 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 final regulated output voltage. This pin is also used as
the short-circuit latchoff timer.
I_TH1, I_TH2 (Pin 27, Pin 1/Pin 11, Pin 13): Error Amplifier
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 2/Pin 10, Pin 12): Receives the
remotely sensed feedback voltage for each controller from
an external resistive divider across the output.
SENSE1⁺, SENSE2⁺ (Pin 1, Pin 3/Pin 9, 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.
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