ics8535-21 Integrated Device Technology, ics8535-21 Datasheet - Page 10

• Manufacturer Part Number: ics8535-21
• Description: Low Skew, 1-to-2 Lvcmos/lvttl-to-3.3v Lvpecl Fanout Buffer
• Manufacturer: Integrated Device Technology

Power Considerations
This section provides information on power dissipation and junction temperature for the ICS535-21.
Equations and example calculations are also provided.
1.
The total power dissipation for the ICS8535-21 is the sum of the core power plus the power dissipated in the load(s).
The following is the power dissipation for V
NOTE: Please refer to Section 3 for details on calculating power dissipated in the load.
Total Power_
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.
In order to calculate junction temperature, the appropriate junction-to-ambient thermal resistance θ
air flow of 200 linear feet per minute and a multi-layer board, the appropriate value is 85.5°C/W per Table 6 below.
Therefore, Tj for an ambient temperature of 70°C with all outputs switching is:
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 6. Thermal Resitance
IDT™ / ICS™ 3.3V LVPECL FANOUT BUFFER
Linear Feet per Minute
Single-Layer PCB, JEDEC Standard Test Boards
Multi-Layer PCB, JEDEC Standard Test Boards
ICS8535-21
LOW SKEW, 1-TO-2 LVCMOS/LVTTL-TO-3.3V LVPECL FANOUT BUFFER
Power Dissipation.
•
•
Power (core)
Power (outputs)
If all outputs are loaded, the total power is 2 * 30mW = 60mW
The equation for Tj is as follows: Tj = θ
Tj = Junction Temperature
θ
Pd_total = Total Device Power Dissipation (example calculation is in section 1 above)
T
70°C + 0.233W * 85.5°C/W = 90°C. This is well below the limit of 125°C.
JA
A
= Ambient Temperature
= Junction-to-Ambient Thermal Resistance
MAX
(3.3V, with all outputs switching) = 173.25mW + 60mW = 233.25mW
MAX
MAX
= V
= 30mW/Loaded Output pair
CC_MAX
θ
JA
for 48 Lead TQFP, Forced Convection
* I
EE_MAX
CC
= 3.3V + 5% = 3.465V, which gives worst case results.
JA
= 3.465V * 50mA = 173.25mW
* Pd_total + T
θ
146.4°C/W
JA
93.2°C/W
vs. Air Flow
A
0
10
125.2°C/W
85.5°C/W
200
ICS8535AG-21 REV. A FEBRUARY 24, 2009
JA
must be used. Assuming a moderate
112.1°C/W
81.2°C/W
500