LTC3889 datasheet(16/118 Pages) AD

16 / 118 page

LTC3888/LTC3888-1/

LTC3888-2

Rev. B

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PIN FUNCTIONS

RUN0/RUN1(Pin20/Pin21):RunControlInputsandOpen-

Drain Outputs. A voltage above 1.5V (LTC3888/3888-2)

and 2V (LTC3888-1) is required on these pins to enable the

respective PWM master channel. The LTC3888/3888-1/

3888-2 may drive these pins low under certain reset/

restart conditions regardless of any PMBus command

settings. A pullup resistor is required in the application.

RSET (Pin 22): Resistor Configuration Set Input. Connect

a 1% 18.7kΩ resistor between this pin and GND to set

the selection values for the configuration resistors for

programming bus address, output current limit and other

PWM settings. Refer to the Applications Information sec-

tion for more details.

ASEL0/ASEL1 (Pin 23, Pin 24): PMBus Serial Address

Select Inputs. Connect optional 1% resistors between

these pins and GND to select the serial bus interface

address. Refer to the Applications Information section

for more detail.

VOUT0_CFG/VOUT1_CFG (LTC3888/3888-2), ILIM0_

CFG/ILIM1_CFG (LTC3888-1) (Pin 25/Pin 26): Output

Voltage (LTC3888/3888-2), Output Current Limit

(LTC3888-1) Configuration Inputs. Connect optional 1%

resistors between these pins and GND to select the output

current limit for each channel. Refer to the Applications

Information section for more detail.

PWM_CFG (Pin 27): PWM Configuration Input. Connect

an optional 1% resistor between this pin and GND to con-

figure PWM switching frequency and master/slave con-

figuration. Refer to the Applications Information section

for more detail.

VDD25 (Pin 28): Internal 2.5V Regulator Output. Bypass

this pin to GND with a low ESR 1μF capacitor. Do not load

this pin with external current.

SDI (LTC3888 Pin 12): Serial Data Input. This pin pro-

vides input data for the Serial Peripheral Interface (SPI).

Ground this pin if not used.

SCK (LTC3888 Pin 13): Serial Clock Input. This pin pro-

vides the input data clock for the SPI. Ground this pin if

not used.

SERR (LTC3888 Pin 34): Open-Drain SPI Status Output.

This pin is pulled low if a SPI transmission error is

detected. Do not wire this pin to a standard (shared) SPI

SDO line. Refer to the Operation section for more detail.

A pull-up resistor is required in the application. This pin

should be left open if not used.

SCS (LTC3888 Pin 35): SPI Chip Select Input. This active-

low input is used to enable the LTC3888 to receive a SPI

data transmission. Wire this pin to VDD33 if not used.

SHARE_CLK (Pin 29): Share Clock Input and Open-

Drain Output. Share clock, nominally 100kHz, is used to

sequence multiple rails in a power system utilizing more

than one ADI PMBus controller. A pull-up resistor to 3.3V

is required in the application. Minimize the capacitance

on this line to ensure the time constant is fast enough for

the application.

VDD33 (Pin 30): Internal 3.3V Regulator Output. Bypass

this pin to GND with a low ESR capacitor (1µF to 2.2µF).

The LTC3888/3888-1/3888-2 may also be powered from

an external 3.3V source attached to this pin for program-

ming purposes only, if the device is otherwise unpow-

ered. Connect only external passive components for

LTC3888/3888-1/3888-2 configuration and application.

INTVCC (Pin 31): 5.2V Regulator Output. Bypass this pin

to GND with a low ESR 4.7μF capacitor. Connect only

external passive components for LTC3888/3888-1/3888-2

configuration and application.

VIN (Pin 32): Main Input Supply. Decouple this pin to GND

with a low ESR capacitor (0.1µF to 2.2µF). In applications

where VIN will always operate below 6V, short this pin and

INTVCC together.

IREF (Pin 33): DrMOS Current Sense Reference. This

voltage output provides reference bias for floating current

monitors from DrMOS devices. Decouple this pin to GND

(exposed pad) at the LTC3888/3888-1/3888-2 and each

power stage with 100nF to 1μF using low ESR capacitors.

GND (Exposed Pad Pin 53): Ground. All small-signal and

compensation components should connect to this pad.

The exposed pad must be soldered to a suitable PCB cop-

per ground plane for proper electrical operation and to

obtain the specified package thermal resistance.

LTC3889 Datasheet(PDF) 16 Page - Analog Devices

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