Integrated
Circuit
Systems, Inc.
ICS84320-01
780MH
Z
, C
RYSTAL
-
TO
-3.3V D
IFFERENTIAL
LVPECL F
REQUENCY
S
YNTHESIZER
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.
V
CCO
Q1
V
OUT
RL
50
V
CCO
- 2V
F
IGURE
6. LVPECL D
RIVER
C
IRCUIT
AND
T
ERMINATION
T
o calculate worst case power dissipation into the load, use the following equations which assume a 50Ω load, and a termination
voltage of V
•
- 2V.
=
V
– 1.0V
CCO
For logic high, V
OUT
= V
(V
CCO_MAX
OH_MAX
CCO_MAX
-V
OH_MAX
) =
1.0V
=
V
– 1.7V
•
For logic low, V
OUT
= V
(V
CCO_MAX
OL_MAX
CCO_MAX
-V
OL_MAX
) =
1.7V
Pd_H is power dissipation when the output drives high.
Pd_L is the power dissipation when the output drives low.
Pd_H = [(V
– (V
- 2V))/R ] * (V
L
OH_MAX
CCO_MAX
CCO_MAX
-V
OH_MAX
) = [(2V - (V
CCO_MAX
-V
OH_MAX
))/R ] * (V
L
CCO_MAX
-V
OH_MAX
)=
[(2V - 1V)/50Ω) * 1V =
20.0mW
Pd_L = [(V
OL_MAX
– (V
CCO_MAX
- 2V))/R ] * (V
L
CCO_MAX
-V
OL_MAX
) = [(2V - (V
CCO_MAX
-V
OL_MAX
))/R ] * (V
L
CCO_MAX
-V
OL_MAX
)=
[(2V - 1.7V)/50Ω) * 1.7V =
10.2mW
Total Power Dissipation per output pair = Pd_H + Pd_L =
30.2mW
84320AY-01
www.icst.com/products/hiperclocks.html
13
REV. A AUGUST 24, 2004
ICS [ INTEGRATED CIRCUIT SYSTEMS ]
