P R E L I M I N A R Y
Table 10. Junction Temperature Calculation
Typical Ambient Temperatures
Speed/
Pkg/
Board
The typical ambient temperature specifications are
based on the following assumptions and calculations:
TJ = TC + ( P θJC
)
TC
P
θJC
TJ
The commercial operating range of the Am186EM and
Am188EM microcontrollers 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 tem-
perature causes a proportional increase in TC.
40/P2
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
1.239
1.239
7
10
5
108.7
112.4
106.2
107.4
107.5
110.7
105.3
106.4
105.7
108.1
104.1
104.9
104.5
106.5
103.2
103.9
40/T2
40/P4–6
40/T4–6
33/P2
1.239
1.239
6
1.07085
1.07085
1.07085
1.07085
0.81125
0.81125
0.81125
0.81125
0.649
7
The 40-MHz microcontroller is specified as 5.0 V, plus
or minus 5%. Therefore, 5.25 V is used for calculating
typical power consumption on the 40-MHz microcon-
troller.
33/T2
10
5
33/P4–6
33/T4–6
25/P2
6
Microcontrollers up to 33 MHz are specified as 5.0 V,
plus or minus 10%. Therefore, 5.5 V is used for calcu-
lating typical power consumption up to 33 MHz.
7
25/T2
10
5
25/P4–6
25/T4–6
20/P2
Typical power supply current (ICC) in normal usage is es-
timated at 5.9 mA per MHz of microcontroller clock rate.
6
7
Typical power consumption (watts) = (5.9 mA/MHz)
times microcontroller clock rate times voltage divided
by 1000.
20/T2
0.649
10
5
20/P4–6
20/T4–6
0.649
0.649
6
Table 9 shows the variables that are used to calculate
the typical power consumption value for each version
of the Am186EM and Am188EM microcontrollers.
By using TJ from Table 10, the typical power consumption
value from Table 9, and a θJA value from Table 8, the typ-
ical ambient temperature TA can be calculated using the
following formula from Figure 16.
Table 9. Typical Power Consumption
Calculation
Typical
Power (P) in
Watts
P = MHz ICC Volts / 1000
TA = TJ – ( P θJA
)
MHz
Typical ICC
Volts
For example, TA for a 40-MHz PQFP design with a 2-
layer board and 0 fpm airflow is calculated as follows:
40
33
25
20
5.9
5.9
5.9
5.9
5.25
5.5
5.5
5.5
1.239
1.07085
0.81125
0.649
TA = 108.673 – ( 1.239 45 )
TA = 52.918
In this calculation, TJ comes from Table 10, P comes
from Table 9, and θJA comes from Table 8. See 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:
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 following formulas from Figure 16 and the
variables in Table 8.
TA = 106.4251 – ( 1.07085 28 )
TA = 76.4413
See Table 14 for the result of this calculation.
By using the maximum case rating TC, the typical
power consumption value from Table 9, and θJC from
Table 8, the junction temperature TJ can be calculated
by using the following formula from Figure 16.
Table 11 through Table 14 and Figure 17 through Fig-
ure 20 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 10 shows TJ values for the various versions of the
Am186EM and Am188EM microcontrollers. The column
titled Speed/Pkg/Board in Table 10 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).
Am186/188EM and Am186/188EMLV Microcontrollers
55
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