87321I Data Sheet
©2016 Integrated Device Technology, Inc Revision A January 25, 201612
This section provides information on power dissipation and junction temperature for the 87321I.
Equations and example calculations are also provided.
1. Power Dissipation.
The total power dissipation for the 87321I is the sum of the core power plus the power dissipated in the load(s).
The following is the power dissipation for V
= 3.465V, which gives worst case results.
NOTE: Please refer to Section 3 for details on calculating power dissipation into the load.
• Power (core)
= 3.465V * 18mA = 62.37mW
• Power (outputs)
= 30mW/Loaded Output pair
(3.465V, with outputs switching) = 62.37mW + 30mW = 92.37mW
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
devices is 125°C.
The equation for Tj is as follows: Tj = θJA * Pd_total + TA
Tj = Junction Temperature
JA = Junction-to-Ambient Thermal Resistance
Pd_total = Total Device Power Dissipation (example calculation is in section 1 above)
= Ambient Temperature
In order to calculate junction temperature, the appropriate junction-to-ambient thermal resistance θ
must be used. Assuming no air ﬂ ow
and a multi-layer board, the appropriate value is 95.0°C/W per Table 6 below.
Therefore, Tj for an ambient temperature of 85°C with output switching is:
85°C + 0.092W *95°C/W = 93.7°C. This is well 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 ﬂ ow,
and the type of board (multi-layer).
TABLE 6. THERMAL RESISTANCE θ
FOR 8-PIN SOIC, FORCED CONVECTION
by Velocity (Linear Feet per Minute)
0 200 500
Multi-Layer PCB, JEDEC Standard Test Boards 95.0°C/W 88.4°C/W 83.7°C/W