Table 12. 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
TC
P
θJC
7
TJ
The commercial operating range of the Am186ER and
Am188ER 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
temperature causes a proportional increase in TC.
50/P2
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
0.662
0.662
0.662
0.662
0.522
0.522
0.522
0.522
0.432
0.432
0.432
0.432
0.342
0.342
0.342
0.342
104.6
106.6
103.3
104.0
103.7
105.2
102.6
103.1
103.0
104.3
102.2
102.6
102.4
103.4
101.7
102.1
50/T2
10
5
50/P4–6
50/T4–6
40/P2
6
The 50-MHz microcontroller is specified as 3.3 V, plus
or minus 10%. Therefore, 3.6 V is used for calculating
typical power consumption on the 50-MHz
microcontroller.
7
40/T2
10
5
40/P4–6
40/T4–6
33/P2
6
Typical power supply current (ICC) in normal usage is
estimated at 3.7 mA per MHz of microcontroller clock
rate.
7
33/T2
10
5
33/P4–6
33/T4–6
25/P2
Typical power consumption can be calculated using the
following formula:
6
7
(Watts) = (3.7 mA/MHz) 50 MHz (3.6 V/1000)
25/T2
10
5
Table 11 shows the variables that are used to calculate
the typical power consumption value for each version
of the Am186ER and Am188ER microcontrollers.
25/P4–6
25/T4–6
6
By using TJ from Table 12, the typical power
consumption value from Table 11, and a θJA value from
Table 10, the typical ambient temperature TA can be
calculated using the following formula from Figure 17.
Table 11. Typical Power Consumption Calculation
P = MHz ICC Volts / 1000
Typical
Power (P)
in Watts
MHz
Typical ICC
Volts
TA = TJ – (P θJA
)
50
40
33
25
3.7
3.7
3.7
3.7
3.6
3.6
3.6
3.6
0.662
0.522
0.432
0.342
For example, TA for a 50-MHz PQFP design with a
2-layer board and 0 fpm airflow is calculated as follows:
TA = 104.6 – (0.662 45)
TA = 74.81
In this calculation, TJ comes from Table 12, P comes
from Table 11, and θJA comes from Table 10. See Table
13.
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 17 and the
variables in Table 10.
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 11, and θJC from
Table 10, the junction temperature TJ can be calculated
by using the following formula from Figure 17.
TA = 102.6 – (0.432 28)
TA = 90.5
See Table 16 for the result of this calculation.
Table 13 through Table 16 and Figure 18 through
Figure 21 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 12 shows TJ values for the various versions of the
Am186ER and Am188ER microcontrollers. The
Speed/Pkg/Board column in Table 12 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).
62
Am186TMER and Am188TMER Microcontrollers Data Sheet
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