LTC7803 datasheet(12/42 Pages) AD

12 / 42 page

LTC7811

Rev. 0

For more information www.analog.com

PIN FUNCTIONS

SW2, SW1 (Pins 19, 31): Switch Node Connections

to Inductors.

BOOST2, BOOST1 (Pins 20, 30): Bootstrapped Supplies

to the Top Side Floating Drivers. Connect capacitors

between the corresponding BOOST and SW pins for

each channel. Also connect Schottky diodes between the

BOOST1 and INTVCC pins, and BOOST2 and the INTVCC

pins. Voltage swing at the BOOST1,2 pins is from INTVCC

to (VIN+INTVCC).

BG2, BG3, BG1 (Pins 21, 25, 29): High Current Gate

Drives for Bottom N-Channel MOSFETs. Voltage swing at

these pins is from ground to INTVCC.

INTVCC (Pin 22): Output of the Internal 5.1V Low Dropout

Regulator. The driver and control circuits are powered by

this supply. Must be decoupled to ground with a minimum

of 4.7μF ceramic or tantalum capacitor.

EXTVCC (Pin 23): External Power Input to an Internal LDO

Connected to INTVCC. This LDO supplies INTVCC power,

bypassing the internal LDO powered from VBIAS whenever

EXTVCC is higher than 4.7V. See INTVCC Regulators in the

Applications Information section. Do not exceed 30V on

this pin. Connect this pin to ground if the EXTVCC LDO

is not used.

VBIAS (Pin 24): Main Bias Input Supply Pin. A bypass

capacitor should be tied between this pin and ground.

BATTSNS (Pin 26): Battery Monitor Input. Connect to a

battery or other supply to use the battery monitor feature.

When the voltage on this pin is below 9.5V, BATTGOOD is

pulled to ground. Connect to ground if the battery moni-

tor feature is not used.

NC (Pins 27, 28): No Internal Connection. Float these pins

or connect to ground.

PGOOD1 (Pin 33): Open-Drain Power Good Output. The

VFB1 pin is monitored to ensure that VOUT1 is in regulation.

When VOUT1 is not within ±10% of its regulation point,

the PGOOD1 pin is pulled low.

PLLIN/SPREAD (Pin 34): External Synchronization Input

and Spread Spectrum Selection. When an external clock

is applied to this pin, the phase-locked loop will force

the rising TG1 signal to be synchronized with the ris-

ing edge of the external clock. When an external clock is

present, the regulators operate in pulse-skipping mode if

it is selected by the MODE pin, or in forced continuous

mode otherwise. When not synchronizing to an external

clock, tie this input to INTVCC to enable spread spectrum

dithering of the oscillator or to ground to disable spread

spectrum.

FREQ (Pin 40): Frequency Control Pin for the Internal

Oscillator. Connect to ground to set the switching fre-

quency to 380kHz. Connect to INTVCC to set the switch-

ing frequency to 2.25MHz. Frequencies between 100kHz

and 3MHz can be programmed using a resistor between

the FREQ pin and ground. Minimize the capacitance on

this pin.

GND (Exposed Pad Pin 41): Ground. Connects to the

sources of bottom N-channel MOSFETs and the (–)

terminal(s) of decoupling capacitors. The exposed pad

must be soldered to PCB ground for rated electrical and

thermal performance.

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