841S012DI Datasheet

©2016 Integrated Device Technology, Inc

January 4, 2016

17

TABLE 7. THERMAL RESISTANCE

θ

JA

FOR

56 LEAD VFQFN, FORCED CONVECTION

2. Junction Temperature.

Junction temperature, Tj, is the temperature at the junction of the bond wire and bond pad and directly affects the reliability of

the device. The maximum recommended junction temperature for HiPerClockS

TM devices is 125°C.

The equation for Tj is as follows: Tj =

θJA * Pd_total + TA

Tj = Junction Temperature

θJA = Junction-to-Ambient Thermal Resistance

Pd_total = Total Device Power Dissipation (example calculation is in section 1 above)

TA = Ambient Temperature

In order to calculate junction temperature, the appropriate junction-to-ambient thermal resistance

θJAmust be used. Assuming 1

meter per second air flow and a multi-layer board, the appropriate value is 27.5°C/W per Table 7.

Therefore, Tj for an ambient temperature of 85°C with all outputs switching is:

85°C + 1.396W * 27.5°C/W = 123.4°C. This is below the limit of 125°C.

This calculation is only an example. Tj will obviously vary depending on the number of loaded outputs, supply voltage, air flow,

and the type of board (multi-layer).

θ

JA

by Velocity (Meters per second)

0

1

2.5

Multi-Layer PCB, JEDEC Standard Test Boards

31.4°C/W

27.5°C/W

24.6°C/W