ICS849S625I Datasheet, PDF (18/24 Pages) Integrated Device Technology – Ten selectable differential LVPECL or LVDS outputs

ICS849S625I Data Sheet
CRYSTAL-TO-LVPECL/LVDS CLOCK SYNTHESIZER
3. Calculations and Equations.
The purpose of this section is to calculate the power dissipation for the LVPECL output pair.
LVPECL output driver circuit and termination are shown in Figure 6.
V_CCO
Q1
V_OUT
RL
50Ω
V_CCO - 2V
Figure 6. LVPECL Driver Circuit and Termination
To calculate worst case power dissipation into the load, use the following equations which assume a 50 load, and a termination voltage of
V_CCO – 2V.
• For logic high, V_OUT = V_{OH_MAX} = V_{CCO_MAX} – 0.7V
(V_{CCO_MAX} – V_{OH_MAX}) = 0.7V
• For logic low, V_OUT = V_{OL_MAX} = V_{CCO_MAX} – 1.5V
(V_{CCO_MAX} – V_{OL_MAX}) = 1.5V
Pd_H is power dissipation when the output drives high.
Pd_L is the power dissipation when the output drives low.
Pd_H = [(V_{OH_MAX} – (V_{CCO_MAX} – 2V))/R_L] * (V_{CCO_MAX} – V_{OH_MAX}) = [(2V – (V_{CCO_MAX} – V_{OH_MAX}))/R_L] * (V_{CCO_MAX} – V_{OH_MAX}) =
[(2V – 0.7V)/50] * 0.7V = 18.2mW
Pd_L = [(V_{OL_MAX} – (V_{CCO_MAX} – 2V))/R_L] * (V_{CCO_MAX} – V_{OL_MAX}) = [(2V – (V_{CCO_MAX} – V_{OL_MAX}))/R_L] * (V_{CCO_MAX} – V_{OL_MAX}) =
[(2V – 1.5V)/50] * 1.5V = 15mW
Total Power Dissipation per output pair = Pd_H + Pd_L = 33.2mW
ICS849S625BYI REVISION A OCTOBER 1, 2012
18
©2012 Integrated Device Technology, Inc.