SC667201MMG3 datasheet(60/120 Pages) FREESCALE

60 / 120 page

MPC5642A Microcontroller Data Sheet, Rev. 3.1

Freescale Semiconductor

Electrical characteristics

As a general rule, the value obtained on a single-layer board is within the normal range for the tightly packed printed circuit

board. The value obtained on a board with the internal planes is usually within the normal range if the application board has:

•

One oz. (35 micron nominal thickness) internal planes

•

Components that are well separated

•

Overall power dissipation on the board is less than 0.02 W/cm2

The thermal performance of any component depends on the power dissipation of the surrounding components. In addition, the

ambient temperature varies widely within the application. For many natural convection and especially closed-box applications,

the board temperature at the perimeter (edge) of the package is approximately the same as the local air temperature near the

device. Specifying the local ambient conditions explicitly as the board temperature provides a more precise description of the

local ambient conditions that determine the temperature of the device.

At a known board temperature, the junction temperature is estimated using Equation 2:

TJ = TB + (RJB * PD)

Eqn. 2

where:

TB = board temperature for the package perimeter (°C)

RJB = junction-to-board thermal resistance (°C/W) per JESD51-8S

PD = power dissipation in the package (W)

When the heat loss from the package case to the air does not factor into the calculation, an acceptable value for the junction

temperature is predictable. Ensure the application board is similar to the thermal test condition, with the component soldered to

a board with internal planes.

The thermal resistance is expressed as the sum of a junction-to-case thermal resistance plus a case-to-ambient thermal

resistance:

RJA = RJC + RCA

Eqn. 3

where:

RJA = junction-to-ambient thermal resistance (°C/W)

RJC = junction-to-case thermal resistance (°C/W)

RCA = case to ambient thermal resistance (°C/W)

RJC is device-related and is not affected by other factors. The thermal environment can be controlled to change the

case-to-ambient thermal resistance, RCA. For example, change the air flow around the device, add a heat sink, change the

mounting arrangement on the printed circuit board, or change the thermal dissipation on the printed circuit board surrounding

the device. This description is most useful for packages with heat sinks where 90% of the heat flow is through the case to heat

sink to ambient. For most packages, a better model is required.

A more accurate two-resistor thermal model can be constructed from the junction-to-board thermal resistance and the

junction-to-case thermal resistance. The junction-to-case thermal resistance describes when using a heat sink or where a

substantial amount of heat is dissipated from the top of the package. The junction-to-board thermal resistance describes the

thermal performance when most of the heat is conducted to the printed circuit board. This model can be used to generate simple

estimations and for computational fluid dynamics (CFD) thermal models.

To determine the junction temperature of the device in the application on a prototype board, use the thermal characterization

parameter (

JT) to determine the junction temperature by measuring the temperature at the top center of the package case using

Equation 4:

TJ = TT + (JT x PD)

Eqn. 4

where:

TT = thermocouple temperature on top of the package (°C)

SC667201MMG3 датащи(PDF) 60 Page - Freescale Semiconductor, Inc

SC667201MMG3 датащи(HTML) 60 Page - Freescale Semiconductor, Inc

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 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

датащи скачать

ссылки URL