5.14 Thermal Resistance Characteristics, 128-Pin PDT (TQFP) Package
over operating free-air temperature range (unless otherwise noted) THERMAL METRIC | VALUE | UNIT |
θJA |
Thermal resistance (junction to ambient) (1) |
44.2 |
°C/W |
θJB |
Thermal resistance (junction to board) (1) |
22.4 |
°C/W |
θJC |
Thermal resistance (junction to case) (1) |
6.8 |
°C/W |
ΨJT |
Thermal metric (junction to top of package) |
0.2 |
°C/W |
ΨJB |
Thermal metric (junction to board) |
22.1 |
°C/W |
TJ |
Junction temperature formula |
TC + (P × ΨJT) (2) TPCB + (P × ΨJB) (3) TA + (P × θJA) (4) TB + (P × θJB) (5)(6) |
°C |
(2) TC is the case temperature and P is the device power consumption.
(4) Because θJA is highly variable and based on factors such as board design, chip size, pad size, altitude, and external ambient temperature, TI recommends using the equations that contain ΨJT and ΨJB for best results.
(5) TB is temperature of the board.
(6) θJB is not a pure reflection of the internal resistance of the package because it includes the resistance of the testing board and environment. TI recommends using equations that contain ΨJT and ΨJB for best results.