844002 Datasheet, PDF (11/16 Pages) Integrated Device Technology – Two LVDS outputs

POWER CONSIDERATIONS
844002 DATA SHEET
This section provides information on power dissipation and junction temperature for the 844002.
Equations and example calculations are also provided.
1. Power Dissipation.
The total power dissipation for the 844002 is the sum of the core power plus the power dissipated in the load(s).
The following is the power dissipation for V = 3.3V + 5% = 3.465V, which gives worst case results.
DD
• Power (core) = V * (I + I ) = 3.465V * (105mA + 12mA) = 405.4mW
MAX
DD_MAX
DD_MAX
DDA_MAX
• Power (outputs) = V
*I
= 3.465V * 120mA = 415.8mW
MAX
DDO_MAX DDO_MAX
Total Power = 405.4mW + 415.8mW = 821.2mW
_MAX
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^TM devices is 125°C.
The equation for Tj is as follows: Tj = θJA * Pd_total + TA
Tj = Junction Temperature
qJA = 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 a
moderate air flow of 200 linear feet per minute and a multi-layer board, the appropriate value is 66.6°C/W per Table 6 below.
Therefore, Tj for an ambient temperature of 70°C with all outputs switching is:
70°C + 0.821W * 66.6°C/W = 124.6°C. This is 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 6. THERMAL RESISTANCE θJA FOR 20-LEAD TSSOP, FORCED CONVECTION
θJA by Velocity (Linear Feet per Minute)
Single-Layer PCB, JEDEC Standard Test Boards
Multi-Layer PCB, JEDEC Standard Test Boards
0
114.5°C/W
73.2°C/W
200
98.0°C/W
66.6°C/W
500
88.0°C/W
63.5°C/W
NOTE: Most modern PCB designs use multi-layered boards. The data in the second row pertains to most designs.
REVISION B 6/9/15
11
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