Motorola MC6805R Series User Manual

11.3 POWER CONSIDERATIONS
The average chip-junction temperature
l
T J, in °c can be obtained from:
TJ= TA + (Poe8JA)
Where:
T A
== Ambient T emperatu re, °c
8JA == Package Thermal Resistance, Junction-to-Ambient, °C/W
PO==PINT+ PPORT
PINT == ICC x VCC, Watts - Chip Internal Power
PPORT== Port Power Oissipation, Watts - User Oetermined
(1 )
For most applications PPORT~ PINT and can be neglected. PPORT may become significant if
the device
is configured to drive Oarlington bases or sink LEO loads.
An appropriate relationship between Po and T J (if PPORT is neglected) is:
PO=K+(TJ+273°) (2)
Solving equations 1 and 2 for K gives:
K= Poe(TA + 273°C) +8JAePo2 (3)
Where K is a constant pertaining to the particular part. K can be determined from equation 3 by
measuring Po (at equilibrium) for a known T
A Using this value of K the values of Po and T J can be
obtained by solving equations (1) and (2) iteratively for any value of T A
VCC=5.75V
Figure 11-1. TTL Equivalent Test Load
(Port
B)
Test
Point
30 pF
(Total)
VCC=5.75V
Figure 11-3. TTL Equivalent Test Load
(Ports A and
C)
TestPoint~
r 30 pF ITo""
Figure 11-2. CMOS Equivalent Test Load
(Port A)
Test
Point
~
VCC=5'75V
3.34kO
l' 30 pF (Total)
Figure 11-4. Open-Drain Equivalent Test Load
(Port
C)
11-2

Motorola MC6805R Series Specifications

General

Brand	Motorola
Model	MC6805R Series
Category	Computer Hardware
Language	English