1 OVERVIEW
S1C33L26 TECHNICAL MANUAL
Seiko Epson Corporation
1-23
Thermal Resistance of the Package
1.3.4
The chip temperature of LSI devices tends to increase with the power consumed on the chip. The chip temperature
when encapsulated in a package is calculated from its ambient temperature (Ta), the thermal resistance of the pack-
age (
θ
), and power dissipation (P
D
).
Chip temperature (Tj) = Ta + (P
D
×
θ
) [°C]
Make sure that the chip temperature (Tj) is 125°C or less when the USB function controller is not used, or 100°C or
less while the USB function controller is operating.
Thermal resistance of the TQFP package
1. When mounted on a board (windless condition)
Thermal resistance (
θ
j-a) = 39°C/W (TQFP24), 42°C/W (TQFP15)
This value indicates the thermal resistance of the package when measured under a windless condition, with
the sample mounted on a measurement board (size: 114
×
76
×
1.6 mm thick, FR4/4 layered board).
2. When suspended alone (windless condition)
Thermal resistance = 90–100°C/W
This value indicates the thermal resistance of the package when measured under a windless condition, with
the sample suspended alone.
Thermal resistance of the PFBGA package
1. When mounted on a board (windless condition)
Thermal resistance (
θ
j-a) = 24°C/W (PFBGA12U)
This value indicates the thermal resistance of the package when measured under a windless condition, with
the sample mounted on a measurement board (size: 114.5
×
101.5
×
1.6 mm thick, FR4/4 layered board).
2. When suspended alone (windless condition)
Thermal resistance = 165°C/W
This value indicates the thermal resistance of the package when measured under a windless condition, with
the sample suspended alone.
Note: The thermal resistance of the package varies significantly depending on how it is mounted on the
board and whether forcibly air-cooled.