VITESSE
SEMICONDUCTOR CORPORATION
Data Sheet
2.48832Gb/s 16:1 SONET/SDH
Transceiver with Integrated Clock Generator
VSC8140
Supplies
The VSC8140 is specified as a PECL device with a single positive 3.3V supply. Should the user desire to
use the device in an ECL environment with a negative 3.3V supply, then V will be ground and V will be -
CC
EE
3.3V. If used with V tied to -3.3V, the TTL control signals are still referenced to V
.
EE
EE
Decoupling of the power supplies is a critical element in maintaining the proper operation of the part. It is
recommended that the V power supply be decoupled using a 0.1µF and 0.01µF capacitor placed in parallel
CC
on each V power supply pin as close to the package as possible. If room permits, a 0.001µF capacitor should
CC
also be placed in parallel with the 0.1µF and 0.01µF capacitors mentioned above. Recommended capacitors are
low-inductance ceramic SMT X7R devices. For the 0.1µF capacitor, a 0603 package should be used. The
0.01µF and 0.001µF capacitors can be either 0603 or 0403 packages.
Extra care needs to be taken when decoupling the analog power supply pins (labeled V
). In order to
CCANA
maintain the optimal jitter and loop bandwidth characteristics of the PLL contained in the VSC8140, the analog
power supply pins should be filtered from the main power supply with a 10µH C-L-C pi filter. If preferred, a
ferrite bead may be used to provide the isolation. The 0.1µF and 0.01µF decoupling capacitors are still required
and must be connected to the supply pins between the device and the C-L-C pi filter (or ferrite bead).
For low frequency decoupling, 47µF tantalum low-inductance SMT caps are sprinkled over the board’s
main +3.3V power supply and placed close to the C-L-C pi filter.
If the device is being used in an ECL environment with a -3.3V supply, then all references to decoupling
V
must be changed to V , and all references to decoupling 3.3V must be changed to -3.3V.
EE
CC
Figure 17: PLL Power Supply Decoupling Scheme
10µH
VEE
VEEANA
0.01µF
0.1µF
0.1µF
VCC
VCCANA
VCCANA
Note: VCC can be tied to VCCANA
G52251-0, Rev. 4.0
9/6/00
VITESSE SEMICONDUCTOR CORPORATION
741 Calle Plano, Camarillo, CA 93012 • 805/388-3700 • FAX: 805/987-5896
Page 13
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