LTM4657 datasheet(17/28 Pages) AD

17 / 28 page

LTM4657

Rev. A

For more information www.analog.com

APPLICATIONS INFORMATION

means that is we take the difference in voltage across the

diode measured at two currents with a ratio of 10, the

resulting voltage is 198μV per Kelvin of the junction with

a zero intercept at 0 Kelvin.

The diode connected NPN transistor across the TSENSE+

pin and TSENSE− pin can be used to monitor the internal

temperature of the LTM4657.

Thermal Considerations and Output Current Derating

The thermal resistances reported in the Pin Configuration

section of the data sheet are consistent with those param-

eters defined by JESD 51-12 and are intended for use with

finite element analysis (FEA) software modeling tools that

leverage the outcome of thermal modeling, simulation,

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 JESD 51-12 (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 anticipate 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 Configuration 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 per-

taining 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 JESD 51-12; 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

to a 95mm × 76mm PCB with four layers.

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 reg-

ulator, the bulk of the heat flows out the bottom of

the package, but there is always heat flow out into the

ambient environment. As a result, this thermal resis-

tance 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

component power dissipation flowing through the top

of the package. As the electrical connections of the typ-

ical µModule regulator are on the bottom of the pack-

age, it is rare for an application to operate such that

most of the heat flows from the junction to the top of

the part. As in the case of θJCbottom, this value may be

useful for comparing packages but the test conditions

don’t generally match the user’s application.

4. θJB, the thermal resistance from junction to the printed

circuit board, is the junction-to-board thermal resis-

tance where almost all of the heat flows through the

bottom of the µModule package and into the board,

and is really the sum of the θJCbottom and the thermal

resistance of the bottom of the part through the solder

joints and through a portion of the board. The board

temperature is measured a specified distance from the

package.

A graphical representation of the aforementioned ther-

mal resistances is given in Figure 9; blue resistances are

contained within the μModule regulator, whereas green

resistances are external to the µModule package.

LTM4657 Datasheet(PDF) 17 Page - Analog Devices

LTM4657 Datasheet(HTML) 17 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 25 26 27 28

Datasheet Download

Link URL