LTM8024 datasheet(32/54 Pages) AD

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LTM4655

Rev. 0

For more information www.analog.com

In rare cases where the minimum on-time restric-

tion is violated, the frequency of the affected LTM4655

channel(s) automatically and gradually folds back down to

one-fifth of its programmed switching frequency to allow

VOUTn– to remain in regulation.

Be reminded of Notes 2, and 3 in the Electrical

Characteristics section regarding output current

guidelines.

Input Capacitors, Negative-VOUT– Operation

The LTM4655 achieves low input conducted EMI noise

due to tight layout and high-frequency bypassing of

MOSFETs MTn and MBn within the module itself. A small

APPLICATIONS INFORMATION

Figure 7. Radiated Emissions Scan of the LTM4655. Producing

24VOUT at 7A, from 36VIN. DC2898A Hardware. fSW = 1.2MHz.

Measured in a 10m Chamber. Peak Detect Method

Figure 9. Radiated Emissions Scan of the LTM4655. Producing

–12VOUT at 4A, from 12VIN. DC2899A Hardware. fSW = 700kHz.

Measured in a 10m Chamber. Peak Detect Method

Figure 8. Radiated Emissions Scan of the LTM4655. Producing

–24VOUT at 2A, from 12VIN , DC2899A Hardware. fSW = 1.2MHz.

Measured in a 10m Chamber. Peak Detect Method

filter inductor (400nH) is integrated in the input line (from

VINn to VDn) provides further noise attenuation—again,

local to the switching MOSFETs. The VDn and VINn pins

are available for external input capacitors—CDn and

CINHn—to form a high-frequency � filter. As shown in

the Simplified Block Diagram, the ceramic capacitor CDn

on the LTM4655’s VDn pins handles the majority of the

RMS current into the DC/DC converter power stage and

requires careful selection, for that reason.

To meet the radiated emissions requirements of

EN55022B, an additional filter capacitor, CINOUTn, is

needed—connecting from VINn to VOUTn–. See Figure 7

through Figure 9 for EMI performance.

–10

FREQUENCY (MHz)

830

130

230

330

430

530

630

730

930 1000

4655 F06

[1] HORIZONTAL

[2] VERTICAL

QPK LIMIT

FORMAL

MEAS DIST 10m

SPEC DIST 10m

–10

FREQUENCY (MHz)

830

130

230

330

430

530

630

730

930 1000

4655 F08

[1] HORIZONTAL

[2] VERTICAL

QPK LIMIT

FORMAL

MEAS DIST 10m

SPEC DIST 10m

–10

FREQUENCY (MHz)

830

130

230

330

430

530

630

730

930 1000

4655 F09

[1] HORIZONTAL

[2] VERTICAL

QPK LIMIT

FORMAL

MEAS DIST 10m

SPEC DIST 10m

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