ICS85301
2:1
DIFFERENTIAL-TO-LVPECL MULTIPLEXER
Integrated
Circuit
Systems, Inc.
POWER CONSIDERATIONS
This section provides information on power dissipation and junction temperature for the ICS85301.
Equations and example calculations are also provided.
1. Power Dissipation.
The total power dissipation for the ICS85301 is the sum of the core power plus the power dissipated in the load(s).
The following is the power dissipation for VCC = 3.465V, which gives worst case results.
NOTE: Please refer to Section 3 for details on calculating power dissipated in the load.
•
•
Power (core)MAX = VCC_MAX * IEE_MAX = 3.465V * 26mA = 90.09mW
Power (outputs)MAX = 27.83mW/Loaded Output pair
Total Power_MAX (3.465, with all outputs switching) = 90.09mW + 27.83mW = 117.92mW
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 HiPerClockSTM devices is 125°C.
The equation for Tj is as follows: Tj = θJA * Pd_total + TA
Tj = JunctionTemperature
θJA = Junction-to-AmbientThermal Resistance
Pd_total =Total Device Power Dissipation (example calculation is in section 1 above)
TA = AmbientTemperature
In order to calculate junction temperature, the appropriate junction-to-ambient thermal resistance θJA must be used. Assuming a
moderate air flow of 0 linear feet per minute and a multi-layer board, the appropriate value is 51.5°C/W perTable 6A below.
Therefore, Tj for an ambient temperature of 85°C with all outputs switching is:
85°C + 0.118W * 51.5°C/W = 91.1°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 (single layer or multi-layer).
TABLE 6A. THERMAL RESISTANCE θJA FOR 16-PIN VFQFN, FORCED CONVECTION
θJA at 0 Air Flow (Linear Feet per Minute)
0
Multi-Layer PCB, JEDEC Standard Test Boards
51.5°C/W
TABLE 6B. THERMAL RESISTANCE θJA FOR FOR 16 LEAD TSSOP
θJA byVelocity (Linear Feet per Minute)
0
200
500
Single-Layer PCB, JEDEC Standard Test Boards
Multi-Layer PCB, JEDEC Standard Test Boards
137.1°C/W
89.0°C/W
118.2°C/W
81.8°C/W
106.8°C/W
78.1°C/W
NOTE: Most modern PCB designs use multi-layered boards.The data in the second row pertains to most designs.
85301AK
www.icst.com/products/hiperclocks.html
REV.A JANUARY 16, 2006
13
ICSI [ INTEGRATED CIRCUIT SOLUTION INC ]
