8P34S2106 Datasheet
Pow er Considerations
This section provides information on power dissipation and junction temperature for the 8P34S2106.
Equations and example calculations are also provided.
1. Power Dissipation.
The following is the power dissipation for VDD = 1.8V + 5% = 1.89V, which gives worst case results.
Maximum current at 85°C: VDD_MAX = 1.89V: IDD_MAX = 390mA
Maximum current at 85°C, VDD_MAX = 2.7V: IDD_MAX = 405mA
Power_MAX = VDD_MAX * IDD_MAX = 1.89V * 390mA = 737.1mW
Power_MAX = VDD_MAX * IDD_MAX = 2.7V * 405mA = 1,093.5mW
2. Junction Temperature.
Junction temperature, Tj, is the temperature at the junction of the bond wire and bond pad directly affects the reliability of the device. The
maximum recommended junction temperature is 125°C. Limiting the internal transistor junction temperature, Tj, to 125°C ensures that
the bond wire and bond pad temperature remains below 125°C.
The equation for Tj is as follows: Tj = JA * 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)
TA = Ambient Temperature
In order to calculate junction temperature, the appropriate junction-to-ambient thermal resistance JA must be used. Assuming no air flow
and a multi-layer board, the appropriate value is 24.6°C/W per Table 16.
Therefore, Tj for an ambient temperature of 85°C with all outputs switching is:
85°C + 0.7371W * 24.6°C/W = 103.2°C. This is below the limit of 125°C. (40-VFQFN package, VDDx = 1.89V)
85°C + 1.0935W * 24.6°C/W = 112°C. This is below the limit of 125°C. (40-VFQFN package, VDDx = 2.7V)
85°C + 0.7371W * 32.32°C/W = 108.9°C. This is below the limit of 125°C. (48-WL-CSP package, VDDx = 1.89V)
85°C + 1.0935W * 32.32°C/W = 120.4°C. This is below the limit of 125°C. (48-WL-CSP package, VDDx = 2.7V)
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).
Table 16. Thermal Resistance JA, Forced Convection
JA (°C/W) vs. Air Flow (m/s)
Meters per Second
0
1
2
40-VFQFN Multi-Layer PCB, JEDEC Standard Test Boards
48-WL-CSP Multi-Layer PCB, JEDEC Standard Test Boards
24.6
21.2
19.6
32.32
28.35
26.05
©2017 Integrated Device Technology, Inc.
18
July 5, 2017