LTC1735 datasheet(8/32 Pages) LINER

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LTC3728L-1

3728l1fc

PIN FUNCTIONS

VOSENSE1, VOSENSE2: Error Ampliﬁer Feedback Input.

Receives the remotely-sensed feedback voltage for each

controller from an external resistive divider across the

output.

PLLFLTR: Filter Connection for Phase-Locked Loop. Alter-

natively, this pin can be driven with an AC or DC voltage

source to vary the frequency of the internal oscillator.

PLLIN: External Synchronization Input to Phase Detector.

This pin is internally terminated to SGND with 50kΩ. The

phase-locked loop will force the rising top gate signal of

controller 1 to be synchronized with the rising edge of

the PLLIN signal.

FCB: Forced Continuous Control Input. This input acts

on both controllers and is normally used to regulate a

secondary winding. Pulling this pin below 0.8V will force

continuous synchronous operation.

ITH1, ITH2: Error Ampliﬁer Output and Switching Regulator

Compensation Point. Each associated channels’ current

comparator trip point increases with this control voltage.

SGND: Small Signal Ground. Common to both controllers,

this pin must be routed separately from high current

grounds to the common (–) terminals of the COUT

capacitors.

3.3VOUT: Linear Regulator Output. Capable of supplying

10mA DC with peak currents as high as 50mA.

NC: No Connect.

SENSE2–, SENSE1–:

The (–) Input to the Differential Cur-

rent Comparators.

SENSE2+, SENSE1+:

The (+) Input to the Differential Current

Comparators. The ITH pin voltage and controlled offsets

between the SENSE– and SENSE+ pins in conjunction with

RSENSE set the current trip threshold.

RUN/SS2, RUN/SS1: Combination of soft-start and run

control inputs. A capacitor to ground at each of these pins

sets the ramp time to full output current. Forcing either of

these pins back below 1.0V causes the IC to shut down

the circuitry required for that particular controller.

TG2, TG1: High Current Gate Drives for Top N-Channel

MOSFETs. These are the outputs of ﬂoating drivers with

a voltage swing equal to INTVCC – 0.5V superimposed on

the switch node voltage SW.

SW2, SW1: Switch Node Connections to Inductors. Voltage

swing at these pins is from a Schottky diode (external)

voltage drop below ground to VIN.

BOOST2, BOOST1: Bootstrapped Supplies to the Top

Side Floating Drivers. Capacitors are connected between

the boost and switch pins and Schottky diodes are tied

between the boost and INTVCC pins. Voltage swing at the

boost pins is from INTVCC to (VIN + INTVCC).

BG2, BG1: High Current Gate Drives for Bottom (Synchro-

nous) N-Channel MOSFETs. Voltage swing at these pins

is from ground to INTVCC.

PGND: Driver Power Ground. Connects to the sources of

bottom (synchronous) N-channel MOSFETs, anodes of the

Schottky rectiﬁers and the (–) terminal(s) of CIN.

INTVCC: Output of the Internal 5V Linear Low Dropout

Regulator and the EXTVCC Switch. 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.

EXTVCC: External Power Input to an Internal Switch Con-

nected to INTVCC. This switch closes and supplies VCC

power, bypassing the internallow dropout regulator, when-

ever EXTVCC is higher than 4.7V. See EXTVCC connection

in Applications section. Do not exceed 7V on this pin.

VIN: Main Supply Pin. A bypass capacitor should be tied

between this pin and the signal ground pin.

PGOOD: Open-Drain Logic Output. PGOOD is pulled to

ground when the voltage on either VOSENSE pin is not

within ±7.5% of its set point.

Exposed Pad (UH Package Only): Signal Ground. Must

be soldered to the PCB, providing a local ground for the

control components of the IC, and be tied to the PGND

pin under the IC.

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