MC33291L Просмотр технического описания (PDF) - Freescale Semiconductor

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MC33291L

Eight-Output Switch with Serial Peripheral Interface I/O

Freescale Semiconductor 

FUNCTIONAL DESCRIPTION

conducted with the device mounted on a typical PC board

placed horizontally in a 33 cubic inch still air enclosure. The

PC board was made of FR4 material measuring 2.5 by

2.5 inches, having double-sided circuit traces of 1.0 ounce

copper soldered to each device pin. The board temperature

was measured with thermal couple soldered to the board

surface one inch away from the center of the device. The

ambient temperature of the enclosure was measured with a

second thermal couple located over the center of one inch

distance from device.

THERMAL PERFORMANCE

Figure 21 illustrates the worst case thermal component

parameters values for the 33291L in the 24-lead SOIC wide

body surface mount package. Pins 5, 6, 7, 8, 17, 18, 19, and

20 of the package were connected directly to the lead frame

flag. The parameter values indicated take into account

adjacent output combinations. The characterization was

conducted over power dissipation levels of 0.7 W to 17 W.

The junction-to-ambient temperature resistance was found to

be 40°C/W with a single output active (34°C/W with all

outputs dissipating equal power 0 and the thermal resistance

from junction-to-PC board (Rjunction-board) to be 30°C/W

(board temperature, measure one inch from device center).

The junction-to-heatsink lead resistance was found again to

approximate 10°C/W. Devoting additional PC board metal

around the heatsinking pins for this package improved the

Rpkg from 33° to 31°C/W.

The total power dissipation available is dependent on the

number of outputs enabled at any one time. At 25°C the

RDS(ON) in 450 mΩ with a coefficient of 6500 ppm/°C. For the

junction temperature to remain below 150°C, the maximum

available power dissipation must decrease as the ambient

temperature increases. Figure 24 depicts the per output limit

of current at ambient temperatures necessary when one,

four, or eight outputs are enable ON. Figure 23 illustrates

how the RDS(ON) output value is affected by junction

temperature.

Output 0

Output 1

Output 2

Junction Temperature Node

VD - TD (C°)

(Volts represent Die Surface Temperature)

Output 6

Output 7

Rd0

Cd0

Rd1

Cd1

Rd2

Cd2

Rd6

Cd6

Rd7

Cd7

IPWR (Steady State or Transient)

(1.0 A = 1.0 W of Device Power Dissipation)

Rpkg = Rleads + RPC Board

Flag Temperature Node

Cpkg = Cflag + CPC Board

Package

24-Lead

SOIC

Rdx

(Ω)*

7.0

Cdx

(F)*

0.002

Rpkg

(Ω)*

33

Cpkg

(F)*

0.15

* Ω = °C/W, F = W s/°C, IPWR = W, and VA = °C

Ambient Temperature Node

VA = TA (C°)

(1.0 V = 1°C Ambient Temperature)

Figure 21. Thermal Model (Electrical Equivalent)

Analog Integrated Circuit Device Data

Freescale Semiconductor

33291L

21

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