LTM4643 datasheet(13/28 Pages) AD

13 / 28 page

LTM8051

Rev. 0

For more information www.analog.com

PIN FUNCTIONS

TRSS1/2/3/4 (Pin J2/C2/C1/K2): Output Tracking and

Soft-Start Pin. This pin allows user control of output volt-

age ramp rate during startup. A TRSS

n voltage below

0.8V forces the LTM8051 to regulate the FB

n pin to equal

the TRSS

n pin voltage. When TRSSn is above 0.8V, the

tracking function is disabled and the internal reference

resumes control of the error amplifier. An internal 2μA

pull-up current on this pin allows a capacitor to program

output voltage slew rate. This pin is pulled to ground dur-

ing shutdown and fault conditions; use a series resistor if

driving from a low impedance output. This pin may be left

floating if the soft-start feature is not being used.

SYNC14/23 (Pin F6/E6): External clock synchronization

input. Ground this pin for low ripple Burst Mode opera-

tion at low output loads; this will also disable the CLKOUT

function. Apply a DC voltage between 2.8V and 4.2V for

forced continuous mode operation with spread spectrum

modulation. Float the SYNC

n pin for forced continuous

mode operation without spread spectrum modulation.

Apply a clock source to the SYNC

n pin for synchronization

to an external frequency. The LTM8051 will be in forced

continuous mode when an external frequency is applied.

BLOCK DIAGRAM

8051 BD

VIN1

RUN14

TRSS1

VIN4

TRSS4

VIN23

RUN23

TRSS2

TRSS3

10nF

0.1F

10nF

CURRENT MODE

CONTROLLER

CURRENT MODE

CONTROLLER

CURRENT MODE

CONTROLLER

CURRENT MODE

CONTROLLER

2.2H

249k

10pF

VOUT1

FB1

VOUT4

FB4

HOUSEKEEPING

CIRCUITRY

HOUSEKEEPING

CIRCUITRY

FB2

VOUT2

VOUT3

FB3

3.3nF

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