LTC3853_15 datasheet(8/36 Pages) LINER

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LTC3853

3853fc

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PIN FUNCTIONS

SENSE1+,SENSE2+,SENSE3+(Pins3,5,7):CurrentSense

ComparatorInputs.The(+)inputstothecurrentcompara-

tors are normally connected to DCR sensing networks or

current sensing resistors. SENSE3+ common modes up

to 13.5V, allowing higher VOUT voltages on channel 3.

SENSE1–, SENSE2–, SENSE3– (Pins 4, 6, 8): Current

Sense Comparator Inputs. The (–) inputs to the current

comparatorsareconnectedtotheoutputs.SENSE3–com-

mon modes up to 13.5V, allowing higher VOUT voltages

on channel 3.

VFB1,VFB2,VFB3(Pins9,12,14):ErrorAmplifierFeedback

Inputs. These pins receive the remotely sensed feedback

voltages for each channel from external resistive dividers

across the outputs. Connecting VFB2toVINthrougha200k

resistor enables dual output (2 + 1) mode.

ITH1, ITH2, ITH3 (Pins 10, 13, 15): Current Control Thresh-

olds and Error Amplifier Compensation Points. Each as-

sociated channels’ current comparator tripping threshold

increases with its ITH control voltage. In dual output

(2 + 1) mode, ITH1 and ITH2 need to be shorted externally.

SGND (Pin 11): Signal Ground. All small-signal compo-

nents and compensation components should connect to

this ground, which in turn connects to PGND at one point.

PGOOD3 (Pin 16):Power Good Indicator Output for Phase

3. Open-drain logic out that is pulled to ground when any

channel output exceeds the ±7.5% regulation window,

after the internal 17µs power bad mask timer expires.

PGOOD12 (Pin 17): Power Good Indicator Output for

Phases 1 and 2. Open-drain logic out that is pulled to

ground when any channel output exceeds the ±7.5%

regulation window, after the internal 17µs power bad

mask timer expires.

INTVCC (Pin 22): Internal 5V Regulator Output. The

control circuits are powered from this voltage. Also

provides channel 3 driver power. Decouple this pin to

PGND with a minimum of 4.7µF low ESR tantalum or

ceramic capacitor.

EXTVCC(Pin23):ExternalPowerInputtoanInternalSwitch

Connected to INTVCC. This switch closes and supplies the

IC power, bypassing the internal low dropout regulator,

whenever EXTVCC is higher than 4.7V. Do not exceed 6V

on this pin and ensure VIN > VEXTVCC at all times.

VIN (Pin 24): Main Input Supply. Decouple this pin to

PGND with a capacitor (0.1µF to 1µF).

DRVCC12(Pin29):DriverVoltageInputforChannels 1and

2. Do not exceed 6V on this pin. This pin must be tied to

INTVCC externally.

BG1, BG2, BG3 (Pins 30, 28, 21): Bottom Gate Driver

Outputs. These pins drive the gates of the bottom N-

channel MOSFETs between PGND and INTVCC/DRVCC12.

SW1, SW2, SW3 (Pins 31, 27, 20): Switch Node Con-

nections to Inductors. Voltage swing at these pins is

from a Schottky diode (external) voltage drop below

ground to VIN.

TG1,TG2,TG3(Pins32,26,19):TopGateDriverOutputs.

These are the outputs of floating drivers with a voltage

swing equal to INTVCC superimposed on the switch nodes

voltages.

BOOST1, BOOST2, BOOST3 (Pins 33, 25, 18): Boosted

Floating Driver Supplies. The (+) terminal of the boot-

strap capacitors connect to these pins. These pins swing

from a diode voltage drop below INTVCC up to VIN +

INTVCC.

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