MC68HC05X4 Datasheet, PDF (127/156 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Freescale Semiconductor, Inc.
Electrical Characteristics
Thermal characteristics and power considerations
TJ = TA + (PD • θ_JA)
[1]
where:
T_A = Ambient temperature (°C)
θ_JA = Package thermal resistance, junction-to-ambient (°C/W)
P_D = P_INT + P_I/O (W)
P_INT = Internal chip power = I_DD • V_DD (W)
P_I/O = Power dissipation on input and output pins (user determined)
An approximate relationship between P_D and T_J (if P_I/O is neglected) is:
PD = _{T----J-----+-K----2---7----3-}
[2]
Solving equations [1] and [2] for K gives:
K = PD • (TA + 273) + θ_JA • PD2
[3]
where K is a constant for a particular part. K can be determined by
measuring P_D (at equilibrium) for a known T_A. Using this value of K, the
values of P_D and T_J can be obtained for any value of T_A by solving the
above equations. The package thermal characteristics are shown in
Table 1.
Pins
PA0–7, PB0–7
TX0, TX1
R1
R2
C
3.26kΩ 2.38kΩ 50pF
0.25kΩ 0.25kΩ 50pF
V_DD = 4.5 V
R2
Test
point
C
R1
3-elec
Figure 2. Equivalent test load
Electrical Characteristics
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MC68HC05X4 Rev 1.0