![NXP Semiconductors MPC5746R Скачать руководство пользователя страница 89](http://html1.mh-extra.com/html/nxp-semiconductors/mpc5746r/mpc5746r_datasheet_1721855089.webp)
7. Thermal characterization parameter indicating the temperature difference between package bottom center and the junction
temperature per JEDEC JESD51-12.
Table 59. Thermal characteristics for the 252-pin MAPBGA package 16 removed balls: 12
central, 4 corner peripheral
Rating
Conditions
Symbol
Value
Unit
Junction to Ambient Natural Convection
,
,
Four layer board (2s2p)
R
θ
JA
23.8
°C/W
Junction to Board
Four layer board (2s2p)
R
θ
JB
15.9
°C/W
Junction to Package Lead
Natural Convection
ψ
JB
4.8
°C/W
1. Junction temperature is a function of die size, on-chip power dissipation, package thermal resistance, mounting site
(board) temperature, ambient temperature, air flow, power dissipation of other components on the board, and board
thermal resistance.
2. Per SEMI G38-87 and JEDEC JESD51-2 with the single layer board horizontal.
3. Per JEDEC JESD51-6 with the board horizontal.
4. Thermal resistance between the die and the printed circuit board per JEDEC JESD51-8. Board temperature is measured
on the top surface of the board near the package.
5. Thermal characterization parameter indicating the temperature difference between package bottom center and the junction
temperature per JEDEC JESD51-12.
20.1 General notes for specifications at maximum junction
temperature
An estimation of the chip junction temperature, T
J
, can be obtained from this equation:
T
J
= T
A
+ (R
θ
JA
× P
D
)
where:
• T
A
= ambient temperature for the package (°C)
• R
θ
JA
= junction to ambient thermal resistance (°C/W)
• P
D
= power dissipation in the package (W)
The junction to ambient thermal resistance is an industry standard value that provides a
quick and easy estimation of thermal performance. Unfortunately, there are two values in
common usage: the value determined on a single layer board and the value obtained on a
board with two planes. For packages such as the PBGA, these values can be different by
a factor of two. Which value is closer to the application depends on the power dissipated
by other components on the board. The value obtained on a single layer board is
appropriate for the tightly packed printed circuit board. The value obtained on the board
with the internal planes is usually appropriate if the board has low power dissipation and
the components are well separated.
When a heat sink is used, the thermal resistance is expressed in the following equation as
the sum of a junction-to-case thermal resistance and a case-to-ambient thermal resistance:
R
θ
JA
= R
θ
JC
+ R
θ
CA
Thermal characteristics
SPC5746R Microcontroller Data Sheet, Rev. 6, 06/2017
NXP Semiconductors
89