XPC8255ZUIFBC Datasheet, PDF (10/41 Pages) Texas Instruments – PowerQUICC II Integrated Communications Processor Hardware Specifications

Electrical and Thermal Characteristics
3 _{Rev C.2 silicon only.}
2.2 Thermal Characteristics
Table 4 describes thermal characteristics.
Table 4. Thermal Characteristics
Characteristics
Symbol
Value
Thermal resistance for TBGA
θ_JA
13.07¹
θ_JA
9.55¹
θ_JA
10.48³
θ_JA
7.78³
Note:
1 _{Assumes a single layer board with no thermal vias}
2 _{Natural convection}
3 _{Assumes a four layer board}
Unit
°C/W
°C/W
°C/W
°C/W
Air Flow
NC²
1 m/s
NC
1 m/s
2.3 Power Considerations
The average chip-junction temperature, T_J, in °C can be obtained from the following:
T_J = T_A + (P_D x 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 x V_DD Watts (chip internal power)
P_I/O = power dissipation on input and output pins (determined by user)
For most applications P_I/O < 0.3 x P_INT. If P_I/O is neglected, an approximate relationship between P_D and
T_J is the following:
P_D = K/(T_J + 273° C)
(2)
Solving equations (1) and (2) for K gives:
K = P_D x (T_A + 273° C) + θ_JA x P_D2
(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.
MPC8260 PowerQUICC II Integrated Communications Processor Hardware Specifications, Rev. 2
10
Freescale Semiconductor