STR91XFAX32 Datasheet, PDF (95/99 Pages) STMicroelectronics – ARM966E-S™ 16/32-Bit Flash MCU with Ethernet, USB, CAN, AC motor control, 4 timers, ADC, RTC, DMA

STR91xFAx32 STR91xFAx42 STR91xFAx44
Package mechanical data
9.2
Thermal characteristics
The average chip-junction temperature, T_J must never exceed 125° C.
The average chip-junction temperature, T_J, in degrees Celsius, may be calculated using the
following equation:
T_J = T_A + (P_D x Θ_JA)(1)
Where:
– T_A is the Ambient Temperature in °C,
– Θ_JA is the Package Junction-to-Ambient Thermal Resistance, in ° C/W,
– P_D is the sum of P_INT and P_I/O (P_D = P_INT + P_I/O),
– P_INT is the product of I_DD and V_DD, expressed in Watts. This is the Chip
Internal Power.
P_I/O represents the Power Dissipation on Input and Output Pins;
Most of the time for the applications P_I/O< P_INT and may be neglected. On the other hand,
P_I/O may be significant if the device is configured to drive continuously external modules
and/or memories. The worst case P_INT of the STR91xFA is 500mW (I_DD x V_DD, or 250mA x
2.0V).
An approximate relationship between P_D and T_J (if P_I/O is neglected) is given by:
P_D = K / (T_J + 273°C) (2)
Therefore (solving equations 1 and 2):
K = P_D x (T_A + 273°C) + Θ_JA x P_D2(3)
where:
– K is a constant for the particular part, which may 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 may be obtained by solving
equations (1) and (2) iteratively for any value of T_A.
Table 49. Thermal characteristics
Symbol
Parameter
Θ_JA
Thermal Resistance Junction-Ambient
LQFP 80 - 12 x 12 mm / 0.5 mm pitch
Θ_JA
Thermal Resistance Junction-Ambient
LQFP128 - 14 x 14 mm / 0.4 mm pitch
Θ_JA
Thermal Resistance Junction-Ambient
LFBGA 144 - 10 x 10 x 1.7mm
Value
41.5
38
36.5
Unit
°C/W
°C/W
°C/W
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