8T33FS6111 Datasheet, PDF (17/28 Pages) Integrated Device Technology – Fully differential architecture from input to all outputs

8T33FS6111 DATA SHEET
Power Considerations (LQFP)
The 8T33FS6111 device was designed and characterized to operate within the ambient industrial temperature range of -40°C to +85°C. The
ambient temperature represents the temperature around the device, not the junction temperature. The LQFP package has no EPAD. When
using the device in extreme cases, such as high ambient temperature, external air flow or using less number of outputs or lower supply voltage
such as 2.5V may be required in order to ensure a safe and reliable junction temperature. Extreme care must be taken to avoid exceeding
125°C junction temperature. The power calculation examples below were generated using a maximum ambient temperature and 2.5V supply
voltage. Depending on the applications, the power consumption can be lower or higher. Please contact IDT technical support for any concerns
on calculating the power dissipation for your own specific configuration.
This section provides information on power dissipation and junction temperature for the 8T33FS6111. 
Equations and example calculations are also provided.
1. Power Dissipation
The total power dissipation for the 8T33FS6111 is the sum of the core power plus the power dissipated due to output switching (load). 
The following is the power dissipation for V_DD = 2.5V +5% = 2.625V.
The maximum core current at 85°C is as follows:
I_{EE_MAX} = 95mA
Core
• Power(core) = V_{DD_MAX} * (I_EE) = 2.625V * 95mA = 249.4mW

LVPECL Output
LVPECL driver power dissipation is 33.2mW/Loaded output pair, total power dissipation due to LVPECL outputs switching:
• Power (outputs)_MAX = 33.2mW/Loaded Output pair
If eight outputs are loaded, the total power is 8 * 33.2mW = 265.6mW
Total Power Dissipation
Total Power
= Power (core) + Power (outputs)
= 249.4mW + 265.6mW 
= 515mW
2. Junction Temperature.
Junction temperature, Tj, is the 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 = _JA * Pd_total + T_A
Tj = Junction Temperature
_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 _JA must be used. Assuming no air flow and
a multi-layer board, the appropriate value is 76.1°C/W for LQFP package per Table 7 below.
Therefore, Tj for an ambient temperature of 85°C with all outputs switching is:
85°C + 0.515W *76.1°C/W = 124.2°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 (multi-layer).
Table 7. Thermal Resistance _JA for 32-Lead LQFP
Meters per Second
_JA by Velocity
0
1
2
Multi-Layer PCB, JEDEC Standard Test Boards
76.1
72.4
70.2
REVISION 1 12/02/14
17
LOW VOLTAGE 2.5V/3.3V DIFFERENTIAL LVPECL/HSTL
FANOUT BUFFER