AMD
67
PRELIMINARY
Enhanced Am486 Microprocessor
12
PACKAGE THERMAL
SPECIFICATIONS
The Am486 microprocessor is specified for operation
when T
CASE
(the case temperature) is within the range
of 0
°
C to +85
°
C. T
CASE
can be measured in any envi-
ronment to determine whether the Am486 microproces-
sor is within specified operating range. The case
temperature should be measured at the center of the
top surface opposite the pins.
The ambient temperature (T
A
) is guaranteed as long as
T
CASE
is not violated. The ambient temperature can be
calculated from
θ
JC
and
θ
JA
and from the following equa-
tions:
T
J
= T
CASE
+ P
θ
JC
T
A
= T
J
– P
θ
JA
T
CASE
= T
A
+ P [
θ
JA
–
θ
JC
]
where:
T
J
, T
A
, T
CASE
= Junction, Ambient, and Case Temperature.
θ
JC
,
θ
JA
= Junction-to-Case and Junction-to-Ambient
Thermal Resistance, respectively.
P
= Maximum Power Consumption
The values for
θ
JA
and
θ
JC
are given in Table 21 for the
1.75 sq. in., 168-pin, ceramic PGA. For the 208-pin
SQFP plastic package,
θ
JA
= 14.0 and
θ
JC
= 1.5.
Table 22 shows the T
A
allowable (without exceeding
T
CASE
) at various airflows and operating frequencies
(Clock). Note that T
A
is greatly improved by attaching a
heat sink to the package. P (the maximum power con-
sumption) is calculated by using the maximum I
CC
at
3.3 V as tabulated in the DC Characteristics
*0.350
″
high unidirectional heat sink (Al alloy 6063-T5, 40 mil fin width, 155 mil center-to-center fin spacing).
Table 21. Thermal Resistance (°C/W)
θ
JC
and
θ
JA
for the Am486 CPU in 168-Pin PGA Package
Cooling
Mechanism
θ
JC
θ
JA
vs. Airflow-ft/min. (m/sec)
200
(1.01)
16.5
14.0
0 (0)
400
(2.03)
12.0
600
(3.04)
10.5
800
(4.06)
9.5
1000
(5.07)
9.0
No Heat Sink
1.5
Heat Sink*
2.0
12.0
7.0
5.0
4.0
3.5
3.25
Heat Sink* and fan
2.0
5.0
4.6
4.2
3.8
3.5
3.25
Table 22. Maximum T
A
at Various Airflows in
°
C
Airflow-ft/min. (m/sec)
200
(1.01)
52.3
57.8
63.2
74.1
60.3
72.6
58.6
71.8
52.0
68.5
45.4
65.2
78.5
79.3
77.6
78.6
77.1
78.1
75.1
76.4
73.1
74.7
T
A
by Cooling
Type
Clock
0 (0)
400
(2.03)
62.1
78.5
77.6
77.1
75.1
73.1
80.2
79.6
79.2
77.7
76.3
600
(3.04)
65.4
80.6
80.1
79.7
78.4
77.1
81.1
80.5
80.2
79.1
77.9
800
(4.06)
67.6
81.7
81.3
81.0
80.1
79.1
81.7
81.3
81.0
80.1
79.1
1000
(5.07)
68.7
82.3
81.9
81.7
80.9
80.1
82.3
81.9
81.7
80.9
80.1
T
A
without Heat Sink
66 MHz
66 MHz
75 MHz
80 MHz
100 MHz
120 MHz
66 MHz
75 MHz
80 MHz
100 MHz
120 MHz
T
A
with Heat Sink
T
A
with Heat Sink and
fan