LTM4613 datasheet(19/34 Pages) LINER

19 / 34 page

LTM4651

4651f

For more information www.linear.com/LTM4651

where N is the number of LTM4651 modules in parallel

configuration.

Depending on the duty cycle of operation (EQ. 4), the

output voltage ripple achieved by paralleled, synchronized

LTM4651modulesmaybeconsiderablysmallerthanwhat

is yielded by EQ. 7. Application Note 77 provides a detailed

explanation of multiphase operation (relevant to parallel

LTM4651 applications) pertaining to noise reduction and

output and input ripple current cancellation. Regardless

of ripple current cancellation, it remains important for the

output capacitance of paralleled LTM4651 applications

to be designed for loop stability and transient response.

LTpowerCAD is available for such analysis.

Figure 4 illustrates the RMS ripple current reduction as

a function of the number of interleaved (paralleled and

synchronized) LTM4651 modules—derived from Ap-

plication Note 77.

Radiated EMI Noise

The generation of radiated EMI noise is an inherent disad-

vantageofswitchingregulators.Fastswitchingturn-onand

turn-off of the power MOSFETs—necessary for achieving

high efficiency—create high-frequency (~30MHz+) ∆l/∆t

changes within DC/DC converters. This activity tends to

be the dominant source of high-frequency EMI radiation

in such systems. The high level of device integration

within LTM4651—including optimized gate-driver and

critical front-end � filter inductor—delivers low radiated

EMI noise performance. Figures 5 to 8 show typical ex-

amples of LTM4651 meeting the radiated emission limits

established by EN55022 Class B.

Thermal Considerations and Output Current Derating

The thermal resistances reported in the Pin Configuration

section of this data sheet are consistent with those pa-

rameters defined by JESD51-12 and are intended for use

with finite element analysis (FEA) software modeling tools

that leverage the outcome of thermal modeling, simula-

tion, and correlation to hardware evaluation performed on

a µModule package mounted to a hardware test board.

The motivation for providing these thermal coefficients is

found in JESD51-12 (“Guidelines for Reporting and Using

Electronic Package Thermal Information”).

Many designers may opt to use laboratory equipment

and a test vehicle such as the demo board to predict the

µModule regulator’s thermal performance in their appli-

cation at various electrical and environmental operating

conditions to compliment any FEA activities. Without FEA

software, the thermal resistances reported in the Pin Con-

figuration section are, in and of themselves, not relevant to

providing guidance of thermal performance; instead, the

derating curves provided in this data sheet can be used

in a manner that yields insight and guidance pertaining to

one’s application-usage, and can be adapted to correlate

thermal performance to one’s own application.

The Pin Configuration section gives four thermal coeffi-

cients explicitly defined in JESD51-12; these coefficients

are quoted or paraphrased below:

1. θJA, the thermal resistance from junction to ambient, is

the natural convection junction-to-ambient air thermal

resistance measured in a one cubic foot sealed enclo-

sure. This environment is sometimes referred to as

“still air” although natural convection causes the air to

move. This value is determined with the part mounted

toaJESD51-9definedtestboard,whichdoesnotreflect

an actual application or viable operating condition.

2. θJCbottom, the thermal resistance from junction to the

bottom of the product case, is determined with all of

the component power dissipation flowing through the

bottom of the package. In the typical µModule regulator,

the bulk of the heat flows out the bottom of the pack-

age, but there is always heat flow out into the ambient

environment. As a result, this thermal resistance value

may be useful for comparing packages but the test

conditions don’t generally match the user’s application.

3. θJCtop, the thermal resistance from junction to top of

the product case, is determined with nearly all of the

APPLICATIONS INFORMATION

LTM4613 Datasheet(PDF) 19 Page - Linear Technology

LTM4613 Datasheet(HTML) 19 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

Datasheet Download

Link URL