84320AY-01
www.idt.com
REV. D JULY 26, 2010
15
ICS84320-01
780MHZ, CRYSTAL-TO-3.3V DIFFERENTIAL
LVPECL FREQUENCY SYNTHESIZER
POWER CONSIDERATIONS
This section provides information on power dissipation and junction temperature for the ICS84320-01.
Equations and example calculations are also provided.
1. Power Dissipation.
The total power dissipation for the ICS84320-01 is the sum of the core power plus the power dissipated in the load(s).
The following is the power dissipation for V
CC = 3.3V + 5% = 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 * 155mA = 537.08mW
Power (outputs)
MAX = 30mW/Loaded Output pair
If all outputs are loaded, the total power is 2 * 30mW = 60mW
Total Power
_MAX (3.465V, with all outputs switching) = 537.1mW + 60mW = 597.1mW
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 the devices is 125°C.
The equation for Tj is as follows: Tj =
θ
JA * Pd_total + TA
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 a moderate air flow of 200 linear feet per minute and a multi-layer board, the appropriate value is 42.1°C/W per
Table 8A below.
Therefore, Tj for an ambient temperature of 70°C with all outputs switching is:
70°C + 0.597W * 42.1°C/W = 95.1°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).
θθθθθ
JA by Velocity (Linear Feet per Minute)
0
200
500
Single-Layer PCB, JEDEC Standard Test Boards
67.8°C/W
55.9°C/W
50.1°C/W
Multi-Layer PCB, JEDEC Standard Test Boards
47.9°C/W
42.1°C/W
39.4°C/W
NOTE: Most modern PCB designs use multi-layered boards. The data in the second row pertains to most designs.
TABLE 8A. THERMAL RESISTANCE
θθθθθ
JA
FOR
32-PIN LQFP, FORCED CONVECTION
θθθθθ
JA by Velocity (Linear Feet per Minute)
TABLE 8B. THERMAL RESISTANCE
θθθθθ
JA
FOR
32-PIN VFQFN FORCED CONVECTION
0
Multi-Layer PCB, JEDEC Standard Test Boards
34.8C/W