LTM4650 datasheet(23/38 Pages) AD

23 / 38 page

LTM4652

Rev. 0

For more information www.analog.com

APPLICATIONS INFORMATION

Solving for T, T = –(VG0 – VD)/(dVD/dT) provides the

temperature.

1st Example: Figure 11 for 27°C, or 300K the diode

voltage is 0.598V, thus, 300K = –(1200mV – 598mV)/

–2.0mV/K).

2nd Example: Figure 11 for 75°C, or 350K the diode

voltage is 0.50V, thus, 350K = –(1200mV – 500mV)/

–2.0mV/K).

Converting the Kelvin scale to Celsius is simply taking the

Kelvin temp and subtracting 273 from it.

A typical forward voltage is given in the electrical char-

acteristics section of the data sheet, and Figure 11 is the

plot of this forward voltage. Measure this forward voltage

at 27°C to establish a reference point. Then using the

above expression while measuring the forward voltage

over temperature will provide a general temperature mon-

itor. A bias current on the order of 100µA is appropriate

for generating a typical forward voltage. If preferred,

LTC2997 and similar temperature-monitoring ICs can be

used, instead (see Figure 33).

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 JESD51-9 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—

also defined by JESD51-9 (Test Boards for Area Array

Surface Mount Package Thermal Measurements). 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 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 the 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 typically gives three thermal

coefficients explicitly defined in JESD51-12; these coeffi-

cients 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 Demo Board.

2. θJCbot, the thermal resistance from junction to the

bottom of the product case, is the junction-to-board

thermal resistance with all of the component power

dissipation flowing through the bottom of the package.

In the typical µModule, 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 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

component power dissipation flowing through the top

of the package. As the electrical connections of the

typical µModule are on the bottom of the package, 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 θJCbot, this value may be useful

for comparing packages but the test conditions don’t

generally match the user’s application.

A graphical representation of the aforementioned thermal

resistances is given in Figure 12; blue resistances are

contained within the µModule regulator, whereas green

resistances are external to the µModule.

LTM4650 Datasheet(PDF) 23 Page - Analog Devices

LTM4650 Datasheet(HTML) 23 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 29 30 31 32 33 34 35 36 37 38

Datasheet Download

Link URL