MPC5645B datasheet(45/114 Pages) FREESCALE

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MPC5646C Microcontroller Data Sheet, Rev. 3

Preliminary—Subject to Change Without Notice

Freescale Semiconductor

4.5

Thermal characteristics

4.5.1

Package thermal characteristics

4.5.2

Power considerations

The average chip-junction temperature, TJ, in degrees Celsius, may be calculated using Equation 1:

TJ = TA + (PD  RJA)

Eqn. 1

Where:

TA is the ambient temperature in °C.

RJA is the package junction-to-ambient thermal resistance, in °C/W.

PD is the sum of PINT and PI/O (PD =PINT + PI/O).

PINT is the product of IDD and VDD, expressed in watts. This is the chip internal power.

PI/O represents the power dissipation on input and output pins; user determined.

Table 11. LQFP thermal characteristics1

1 Thermal characteristics are targets based on simulation that are subject to change per device characterization.

Symbol

Parameter

Conditions2

2 V

DD = 3.3 V ± 10% / 5.0 V ± 10%, TA = 40 to 125 °C.

Pin count

Value3

3 All values need to be confirmed during device validation.

Unit

Min

Typ

Max

RJA

Thermal resistance,

junction-to-ambient

natural convection4

4 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.

Single-layer

board—1s

176

—

385

5 Junction-to-Ambient thermal resistance determined per JEDEC JESD51-3 and JESD51-6.

°C/W

208

—

416

6 Junction-to-Ambient thermal resistance determined per JEDEC JESD51-2 and JESD51-6

°C/W

RJA

Thermal resistance,

junction-to-ambient

natural convection7

Four-layer

board—2s2p7

7 Junction-to-Board thermal resistance determined per JEDEC JESD51-8.

176

—

°C/W

208

—

°C/W

Table 12. 256 MAPBGA thermal characteristics1

1 Thermal characteristics are targets based on simulation that are subject to change per device characterization.

Symbol

Parameter

Conditions

Value

Unit

RJA CC — Thermal resistance, junction-to-ambient

natural convection

Single-layer board—1s

432

2 Junction-to-ambient thermal resistance determined per JEDEC JESD51-2 with the single layer board horizontal.

Board meets JESD51-9 specification.

°C/W

Four-layer board—2s2p

263

3 Junction-to-ambient thermal resistance determined per JEDEC JESD51-6 with the board horizontal.

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