mc33291l Freescale Semiconductor, Inc, mc33291l Datasheet - Page 21

• Manufacturer Part Number: mc33291l
• Description: Eight-output Switch With Serial Peripheral Interface I/o
• Manufacturer: Freescale Semiconductor, Inc

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
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.
Analog Integrated Circuit Device Data
Freescale Semiconductor
Figure 21
illustrates the worst case thermal component
*
24-Lead
Package
Ω
SOIC
= °C/W, F = W s/°C, I PWR = W, and V A = °C
I PWR (Steady State or Transient)
(1.0 A = 1.0 W of Device Power Dissipation)
R d0
Rdx
(Ω)*
7.0
Output 0
C d0
0.002
C
(F)*
dx
Figure 21. Thermal Model (Electrical Equivalent)
R d1
R
(Ω)*
33
pkg
Output 1
R pkg = R leads + R PC Board
C d1
C
0.15
(F)*
pkg
R d2
Output 2
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 (R
(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
R
number of outputs enabled at any one time. At 25°C the
R
junction temperature to remain below 150°C, the maximum
available power dissipation must decrease as the ambient
temperature increases.
of current at ambient temperatures necessary when one,
four, or eight outputs are enable ON.
how the R
temperature.
C d2
pkg
DS(ON)
The total power dissipation available is dependent on the
from 33° to 31°C/W.
Flag Temperature Node
in 450 mΩ with a coefficient of 6500 ppm/°C. For the
Junction Temperature Node
V D - T D (C°)
(Volts represent Die Surface Temperature)
Ambient Temperature Node
V A = T A (C°)
(1.0 V = 1°C Ambient Temperature)
DS(ON)
C pkg = C flag + C PC Board
output value is affected by junction
Output 6
Figure 24
R d6
junction-board
FUNCTIONAL DESCRIPTION
C d6
depicts the per output limit
Output 7
Figure 23
) to be 30°C/W
R d7
illustrates
C d7
33291L
21