LTM4636 datasheet(13/36 Pages) LINER

13 / 36 page

LTM4650A-1

4650a1f

For more information www.linear.com/LTM4650A-1

Figure 4. 4-Phase Parallel Configurations

4650a1 F04

60.4k

TRACK1

TRACK2

VOUT1

VOUTS1

VFB1

VFB2

COMP1

4 PARALLELED OUTPUTS

FOR 1.2V AT 100A

OPTIONAL CONNECTION

COMP2

VOUTS2

VOUT2

60.4k

TRACK1

TRACK2

0.1µF

6800pF

2.5k

VOUT1

VOUTS1

VFB1

VFB2

COMP1

COMP2

VOUTS2

VOUT2

60.4k

LTM4650A-1

RFB

60.4k

OPTIONAL

RFB

60.4k

USE TO LOWER

TOTAL EQUIVALENT

RESISTANCE TO LOWER

IFB VOLTAGE ERROR

APPLICATIONS INFORMATION

voltage will default to 0.6V with no feedback resistor on

either VFB1 or VFB2. Adding a resistor RFB from VFB pin to

GND programs the output voltage:

VOUT = 0.6V •

60.4k +RFB

RFB

Table 1. VFB Resistor Table vs Various Output Voltages

VOUT 0.6V

1.0V

1.2V

1.5V

1.8V

2.5V

3.3V

RFB

Open 90.9k 60.4k 40.2k 30.2k 19.1k 13.3k 8.25k

For parallel operation of multiple channels the same feed-

back setting resistor can be used for the parallel design.

This is done by connecting the VOUTS1 to the output as

shown in Figure 4, thus tying one of the internal 60.4k

resistors to the output. All of the VFB pins tie together with

one programming resistor as shown in Figure 4.

Inparalleloperation,theVFBpinshaveanIFBcurrentof20nA

maximumeachchannel.Toreduceoutputvoltageerrordue

to this current, an additional VOUTS pin can be tied to VOUT,

andanadditionalRFBresistorcanbeusedtolowerthetotal

Thevenin equivalent resistance seen by this current. For

exampleinFigure4,thetotalTheveninequivalentresistance

of the VFB pin is (60.4k//RFB), which is 30.2k where RFB is

equal to 60.4k for a 1.2V output. Four phases connected

in parallel equates to a worse case feedback current of

4 • IFB = 80nA maximum. The voltage error is 80nA • 30.2k

= 2.4mV. If VOUTS2 is connected, as shown in Figure 4, to

VOUT,andanother60.4kresistorisconnectedfromVFB2to

ground, then the voltage error is reduced to 1.2mV. If the

voltage error is acceptable then no additional connections

arenecessary.Theonboard60.4kresistoris0.5%accurate

and the VFB resistor can be chosen by the user to be as

accurate as needed. All COMP pins are tied together for

current sharing between the phases. The TRACK/SS pins

can be tied together and a single soft-start capacitor can

be used to soft-start the regulator. The soft-start equation

willneedtohavethesoft-startcurrentparameterincreased

by the number of paralleled channels. See Output Voltage

Tracking section.

Input Capacitors

The LTM4650A-1 module should be connected to a low

AC-impedanceDCsource.Foreachchannelinput,two 22µF

input ceramic capacitors are used for RMS ripple current.

A47µFto100µFsurfacemountaluminumelectrolyticbulk

capacitor can be used for more input bulk capacitance.

This bulk input capacitor is only needed if the input source

impedanceiscompromisedbylonginductiveleads,traces

ornotenoughsourcecapacitance.Iflowimpedancepower

planes are used, then this bulk capacitor is not needed.

For a buck converter, the switching duty-cycle can be

estimated as:

VOUT

VIN

LTM4636 датащи(PDF) 13 Page - Linear Technology

LTM4636 датащи(HTML) 13 Page - Linear Technology

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 25 26 27 28 29 30 31 32 33 34 35 36

датащи скачать

ссылки URL