843022I-02 Datasheet, PDF (12/17 Pages) Integrated Device Technology – FemtoClock® Crystal-to-3.3V, 2.5V LVPECL Clock Generator

843022I-02 DATA SHEET
3. Calculations and Equations.
The purpose of this section is to derive the power dissipated into the load.
LVPECL output driver circuit and termination are shown in Figure 6.
FIGURE 6. LVPECL DRIVER CIRCUIT AND TERMINATION
To calculate worst case power dissipation into the load, use the following equations which assume a 50Ω load, and a termination
voltage of V - 2V.
CC
•
For
logic
high,
V_OUT
=
V
OH_MAX
=
V
CC_MAX
–
0.9V
(V_{CC_MAX} - V ⁾ _{OH_MAX} = 0.9V
•
For
logic
low,
V_OUT
=
V
OL_MAX
=
V–
CC_MAX
1.7V
(V - V ⁾ = 1.7V
CC_MAX
OL_MAX
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 - _{CC_MAX}
2V))/R ]
L
*
(V - _{CC_MAX}
V ) _{OH_MAX}
=
[(2V
-
(V_{CC_MAX}
-
V_{OH_MAX}^))/R_L]
*
(V - _{CC_MAX}
V ) _{OH_MAX}
=
[(2V - 0.9V)/50Ω] * 0.9V = 19.8mW
Pd_L
=
[(V_{OL_MAX} –
(V - _{CC_MAX}
2V))/R ]
L
*
(V - _{CC_MAX}
V ) _{OL_MAX}
=
[(2V
-
(V_{CC_MAX}
-
V_{OL_MAX}^))/R_L]
*
(V - _{CC_MAX}
V ) _{OL_MAX}
=
[(2V - 1.7V)/50Ω] * 1.7V = 10.2mW
Total Power Dissipation per output pair = Pd_H + Pd_L = 30mW
FEMTOCLOCKS™ CRYSTAL-TO-3.3V, 2.5V
12
LVPECL CLOCK GENERATOR
REVISION A 11/4/15