cx28250 Mindspeed Technologies, cx28250 Datasheet - Page 89

• Manufacturer Part Number: cx28250
• Description: Cx28250 Atm Physical Interface Phy Devices
• Manufacturer: Mindspeed Technologies

CX28250
ATM Physical Interface (PHY) Devices
3.2.1 Analog Power
28250-DSH-002-C
3.2 Board Layout
Mindspeed has completed jitter testing of the CX28250-23 OC-3/STM1 PHY
device and verified that it meets all jitter requirements of Bellcore
GR-253-CORE while passing bi-directional traffic at the full line rate.
and the layout is shown in
contact your Field Engineer for details). Complete board layout files, including
Gerber plots, are also available online. The external filter networks and analog
power warrant special attention.
During testing it was found that under normal conditions the device meets all
jitter specifications with significant margin. However, increasing the noise level
on the 3.3 volt supply will eventually impact the intrinsic jitter, especially if the
noise is low frequency, (100 kHz range), non-periodic pulses. The designer has
the following options:
Figure
resistor. The regulator can then be omitted, (“no stuff ”), in production if not
needed.
A partial schematic of the board used by Mindspeed is shown in
• Ensure that their board is electrically quiet. In general, 50-75 mV of white
• Install passive filters on the analog power pins. Unfortunately, due to the
• Provide a separate 3.3 volt regulator for the analog supply pins. This is the
Recommended Layout: Use the layout of the separate regulator as shown in
noise will not affect jitter generation.
low frequencies involved, the inductors required need be in the 2-3 mH
range. These are quite large and expensive.
approach taken by Mindspeed. These devices are relatively inexpensive
and take very little board space. The current requirement is only 150 mA.
3-4. Lay the board out such that the regulator can be bypassed by a 0 Ω
Mindspeed Technologies
Figure 3-3
(the full schematic is available online;
™
3.0 Applications
3.2 Board Layout
Figure 3-2
3-3