P R E L I M I N A R Y
Table 13. Junction Temperature Calculation
Typical Ambient Temperatures
The typical ambient temperature specifications are
based on the following assumptions and calculations:
Speed/
Pkg/
TJ = TC + (P θJC
)
Board
TJ(°C)
108.3
111.8
105.9
107.1
106.8
109.7
104.9
105.8
105.2
107.4
103.7
104.4
104.1
105.9
103.0
103.5
TC
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
P
θJC
7
The commercial operating range of the Am186ED
microcontroller is a case temperature TC of 0 to 100
degrees Centigrade. TC is measured at the top center
of the package. An increase in the ambient temperature
causes a proportional increase in TC.
40/P2
1.2
1.2
1.2
1.2
1.0
1.0
1.0
1.0
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
40/T2
10
5
40/P4-6
40/T4-6
33/P2
6
Microcontrollers up to 40 MHz are specified as 5.0 V
plus or minus 10%. Therefore, 5.0 V is used for
calculating typical power consumption up to 40 MHz.
7
33/T2
10
5
33/P4-6
33/T4-6
25/P2
Typical power supply current (ICC) in normal usage is
estimated at 5.9 mA per MHz of microcontroller clock
rate.
6
7
25/T2
10
5
Typical power consumption (watts) = (5.9 mA/MHz)
times microcontroller clock rate times VCC divided by
1000.
25/P4-6
25/T4-6
20/P2
6
7
Table 12 shows the variables that are used to calculate
the typical power consumption value for each version
of the Am186ED microcontroller.
20/T2
10
5
20/P4-6
20/T4-6
6
Table 12. Typical Power Consumption Calculation
By using TJ from Table 13, the typical power
consumption value from Table 12, and a θJA value from
Table 11, the typical ambient temperature TA can be
calculated using the following formula from Figure 14:
Typical
Power (P) in
P = MHz ICC VCC/1000
Watts
MHz
40
Typical ICC
Volts
TA = TJ – (P θJA
)
5.9
5.9
5.9
5.9
5.0
5.0
5.0
5.0
1.2
1.0
0.7
0.6
For example, TA for a 40-MHz PQFP design with a 2-
layer board and 0 fpm airflow is calculated as follows:
33
25
TA = 108.3 – (1.2 45)
TA = 55.2
20
In this calculation, TJ comes from Table 13, P comes
from Table 12, and θJA comes from Table 11. See Table
14.
Thermal resistance is a measure of the ability of a
package to remove heat from a semiconductor device.
A safe operating range for the device can be calculated
using the formulas from Figure 14 and the variables in
Table 11.
TA for a 33-MHz TQFP design with a 4-layer to 6-layer
board and 200 fpm airflow is calculated as follows:
By using the maximum case rating TC, the typical
power consumption value from Table 12, and θJC from
Table 11, the junction temperature TJ can be calculated
by using the following formula from Figure 14.
TA = 105.8 – (1.0 28)
TA = 78.6
See Table 17 for the result of this calculation.
Table 14 through Table 17 and Figure 15 through
Figure 18 show TA based on the preceding
assumptions and calculations for a range of θJA values
with airflow from 0 linear feet per minute to 600 linear
feet per minute.
TJ = TC + (P θJC
)
Table 13 shows TJ values for the various versions of
the Am186ED microcontroller. The column titled
Speed/Pkg/Board in Table 13 indicates the clock speed
in MHz, the type of package (P for PQFP and T for
TQFP), and the type of board (2 for 2-layer and 4-6 for
4-layer to 6-layer).
52
Am186ED/EDLV Microcontrollers
AMD [ AMD ]
