843201-375 Datasheet, PDF (13/19 Pages) Integrated Device Technology – FemtoClock® Crystal-to-LVPECL 375MHz Frequency Margining Synthesizer

843201-375 DATA SHEET
POWER CONSIDERATIONS
This section provides information on power dissipation and junction temperature for the 843201-375.
Equations and example calculations are also provided.
1. Power Dissipation.
The total power dissipation for the 843201-375 is the sum of the core power plus the power dissipated due to loading.
The following is the power dissipation for V = 3.3V + 5% = 3.465V, which gives worst case results.
CC
NOTE: Please refer to Section 3 for details on calculating power dissipated due to loading.
• Power (core) = V * I = 3.465V * 108mA = 374.2mW
MAX
CC_MAX
EE_MAX
• Power (outputs) = 30mW/Loaded Output pair
MAX
Total Power (3.465V) = 374.2mW + 30mW = 404.2mW
_MAX
2. Junction Temperature.
Junction 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 = θJA * Pd_total + TA
Tj = Junction Temperature
θJA = 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 θJA must be used. Assuming 0 air flow
and a multi-layer board, the appropriate value is 99.9°C/W per Table 8 below.
Therefore, Tj for an ambient temperature of 70°C with all outputs switching is:
70°C + 0.404W * 99.9°C/W = 110°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 8. THERMAL RESISTANCE θJA FOR 16-PIN TSSOP, FORCED CONVECTION
θJA by Velocity (Linear Feet per Minute)
Multi-Layer PCB, JEDEC Standard Test Boards
0
99.9°C/W
200
35.6°C/W
500
93.5°C/W
REVISION A 8/21/15
13
FEMTOCLOCK® CRYSTAL-TO-LVPECL
375MHZ, FREQUENCY MARGINING SYNTHESIZER