ICS854104 Datasheet, PDF (11/15 Pages) Integrated Device Technology – Low Skew, 1-to-4, Differential-to-LVDS Fanout Buffer

ICS854104 Data Sheet
LOW SKEW, 1-TO-4, DIFFERENTIAL-TO-LVDS FANOUT BUFFER
Power Considerations
This section provides information on power dissipation and junction temperature for the ICS854104.
Equations and example calculations are also provided.
1. Power Dissipation.
The total power dissipation for the ICS854104 is the sum of the core power plus the analog power plus the power dissipated in the load(s). The
following is the power dissipation for V_DD = 3.3V + 5% = 3.465V, which gives worst case results.
• Power (core)_MAX = V_{DD_MAX} * I_{DD_MAX} = 3.465V * 75mA = 259.875mW
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 for HiPerClockS devices 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 = θ_JA * Pd_total + T_A
Tj = Junction Temperature
θ_JA = Junction-to-Ambient Thermal Resistance
Pd_total = Total Device Power Dissipation (example calculation is in section 1 above)
T_A = Ambient Temperature
In order to calculate junction temperature, the appropriate junction-to-ambient thermal resistance θ_JA must be used. Assuming no air flow and
a multi-layer board, the appropriate value is 100.3°C/W per Table 6 below.
Therefore, Tj for an ambient temperature of 70°C with all outputs switching is:
70°C + 0.260W * 100.3°C/W = 96.1°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 flow and the type of
board (multi-layer).
Table 6. Thermal Resistance θ_JA for 16 Lead TSSOP, Forced Convection
θ_JA by Velocity
Meters per Second
0
Multi-Layer PCB, JEDEC Standard Test Boards
100.3°C/W
1
96.0°C/W
2.5
93.9°C/W
ICS854104AG REVISION A AUGUST 14, 2009
11
©2009 Integrated Device Technology, Inc.