7.

Thermal Considerations

7.1

Thermal Resistance Data

The following table summarizes the thermal resistance data depending on the package.

Table 7-1. Thermal Resistance Data

Package Type

θJA [°C/W]

θJC [°C/W]

24-pin VQFN (ZHA)

60.6

25

Related Links

Junction Temperature

7.2

Junction Temperature

The average chip-junction temperature, TJ, in °C can be obtained from the following:

1.

TJ = TA + (PD x θJA)

2.

TJ = TA + (PD x (θHEATSINK + θJC))

where:

•

θJA = Package thermal resistance, Junction-to-ambient (°C/W), see Thermal Resistance Data

•

θJC = Package thermal resistance, Junction-to-case thermal resistance (°C/W), see Thermal

Resistance Data

•

θHEATSINK = Thermal resistance (°C/W) specification of the external cooling device

•

PD = Device power consumption (W)

•

TA = Ambient temperature (°C)

From the first equation, the user can derive the estimated lifetime of the chip and decide if a cooling

device is necessary or not. If a cooling device is to be fitted on the chip, the second equation should be

used to compute the resulting average chip-junction temperature TJ in °C.

Related Links

Thermal Resistance Data

ATtiny417/817

© 2017 Microchip Technology Inc.

Datasheet Summary

DS40001934A-page 13