LT8685SRVPBF datasheet(10/24 Pages) AD

10 / 24 page

LT8685S

Rev. 0

For more information www.analog.com

PIN FUNCTIONS

VIN1 (Pin 1): Channel 1 and Internal INTVCC Regulator

Power Supply Input. This pin should be closely decou-

pled to ground with a low ESR capacitor of value 2.2µF

or greater.

VIN2 (Pin 2): Channel 2 Power Supply Input. This pin should

be closely decoupled to ground with a low ESR capacitor

of value 2.2µF or greater. This pin must be shorted to VIN1

when channel 2 is combined with channel 1.

SYNC/MODE (Pin 4): Mode Selection and External

Synchronization Input Pin. This pin places all active

LT8685S channels into high efficiency Burst Mode oper-

ation when tied to ground. Tie this pin to ground with

a 26k (5% tolerance or better) resistor to enable high

efficiency Burst Mode with spread spectrum modula-

tion. Float this pin to enable pulse-skipping mode. Tie

this pin to INTVCC to enable pulse-skipping mode with

spread-spectrum modulation. When this pin is driven by

an external clock source, the LT8685S will synchronize

its switching frequency to that of the external clock and

operate in pulse-skipping mode. Channels 1 to 4 clock

phases default to 0°, 180°, 270°, and 90° respectively

when operating independently. When combining chan-

nels, the master channel determines the operating phase.

See the Applications Information section for more detail.

RT (Pin 5): Switching Frequency Program Pin. Connect

an external resistor from this pin to ground to program

the LT8685S switching frequency from 350kHz to 3MHz.

When using external clock synchronization, an RT resistor

must be selected to match the nominal incoming clock

frequency. See the Applications Information section for

more detail.

VIN3 (Pins 7, 8): Channel 3 Power Supply Input. When

driven from another LT8685S channel, the required

decoupling capacitance for this pin is largely satisfied by

the output capacitance of the driving channel. In this sce-

nario, a low ESR capacitor of value 1µF or greater located

close to the VIN3 pin is generally sufficient. If driven from

an external source, this pin should be closely decoupled

with a low ESR capacitor of value 4.7µF or greater.

VIN4 (Pins 9, 10): Channel 4 Power Supply Input. When

driven from another LT8685S channel, the required

decoupling capacitance for this pin is largely satisfied by

the output capacitance of the driving channel. In this sce-

nario, a low ESR capacitor of value 1µF or greater located

close to the VIN4 pin is generally sufficient. If driven from

an external source, this pin should be closely decoupled

with a low ESR capacitor of value 4.7µF or greater. This

pin must be shorted to VIN3 when channel 4 is combined

with channel 3.

FB3 (Pin 11): Channel 3 Output Voltage Feedback Pin.

Channel 3 regulates this pin to a precision, internal, 0.7V

reference voltage. Connect this pin to the appropriate

resistor divider network to program the desired output

voltage.

FB4 (Pin 13): Channel 4 Output Voltage Feedback Pin.

Channel 4 regulates this pin to a precision, internal, 0.7V

reference voltage. Connect this pin to the appropriate

resistor divider network to program the desired output

voltage. When this pin is tied to INTVCC, channel 4 is com-

bined with channel 3 to create a single output channel with

increased output current capability. See the Applications

Information section for more detail.

INTVCC (Pin 24): Internal Regulator Output Pin. This regu-

lator provides the supply current for the power FET driver

circuits and internal control circuitry. This pin should be

decoupled to ground with a low ESR ceramic capacitor

of value 4.7µF. This capacitor should be placed close to

the INTVCC pin with a low impedance connection to the

exposed pad ground. This supply is not intended as a

power supply output. Do not connect external circuitry

to this pin.

BIAS (Pin 25): External Regulator Input Pin. The inter-

nal regulator, INTVCC, will draw current from this supply

instead of VIN1 when BIAS is tied to a voltage higher than

4.5V and VVIN1 is greater than VBIAS + 1V. Connecting

this pin to a high efficiency supply, such as an LT8685S

output channel regulating to 5V, improves overall effi-

ciency by reducing the on-chip power consumption that

would normally result when drawing current from VIN1.

When used, this pin should be decoupled to ground with

LT8685SRVPBF データシート(PDF) 10 Page - Analog Devices

LT8685SRVPBF データシート(HTML) 10 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

データシートダウンロード