MC68HC05C8A Datasheet, PDF (86/116 Pages) Motorola, Inc – Microcontrollers

Electrical Specifications
13.4 Thermal Characteristics
Characteristic
Thermal resistance
Plastic dual in-line package
Plastic leaded chip carrier (PLCC)
Quad flat pack (QFP0)
Plastic shrink DIP (SDIP)
Symbol
θ_JA
Value
60
70
95
60
Unit
°C/W
13.5 Power Considerations
The average chip-junction temperature, T_J, in °C, can be obtained from:
T_J = T_A + (P_D × 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
P_INT = I_DD × V_DD watts (chip internal power)
P_I/O = Power dissipation on input and output pins (user-determined)
For most applications P_I/O « P_INT and can be neglected.
Following is an approximate relationship between P_D and T_J (neglecting P_I/O):
P_D = K ÷ (T_J + 273 °C)
(2)
Solving equations (1) and (2) for K gives:
K = P_D × (T_A + 273 °C) + θ_JA × (P_D)²
(3)
where K is a constant pertaining to the particular part. K can be determined from equation (3) 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 by solving equations (1) and (2) iteratively for any value of T_A.
TEST
POINT
V_DD
R2
SEE TABLE
V_DD = 4.5 V
Pins
PA7–PA0
PB7–PB0
PC7–PC0
PD5–PD0, PD7
R1
3.26 Ω
C
SEE
TABLE
R1
SEE TABLE
V_DD = 3.0 V
Pins
PA7–PA0
PB7–PB0
PC7–PC0
PD5–PD0, PD7
R1
10.91 Ω
Figure 13-1. Test Load
R2
2.38 Ω
R2
6.32 Ω
C
50 pF
C
50 pF
MC68HC05C8A • MC68HCL05C8A • MC68HSC05C8A Data Sheet, Rev. 5.1
86
Freescale Semiconductor