Passive Filtering; Figure 4-21: Power Supply Circuit Using Lt1963 (Lt1963A) Regulator - Xilinx RocketIO X User Manual

PCB Design Requirements
•
The LT1963 (LT1963A) regulator must be used with the circuit specified by the
manufacturer.
(LT1963A) with values for a 2.5V supply, as would be used for AVCCAUXTX.
Alternatively, fixed output voltage devices in the same series may be used, such as the
LT1963 (LT1963A)-2.5. If the fixed version is used, SENSE should be connected to OUT. A
similar solution must be used for generating 1.5V for AVCCAUXRX and VTTX.
The specified Texas Instruments regulators require a similar solution.
2
V > 3VDC
IN
IN
1
SHDN
5
+
SENSE
10µF
LT1963
GNDA

Figure 4-21: Power Supply Circuit Using LT1963 (LT1963A) Regulator

Termination voltage can be of any value in the range of 0.25V to 2.5V. In cases where the
RocketIO X transceiver is interfacing with a transceiver from another vendor, termination
voltage can be dictated by the specifications of the other transceiver. In cases where the
RocketIO X transceiver is interfacing with another RocketIO X transceiver, a 1.5V termination
voltage is recommended. The LT1963 (LT1963A) circuit's output capacitors (330 µF and 1 µF)
can be placed anywhere on the board, preferably close to the output of the LT1963 device.
All characterization work was done using the LT1963 device. If another part is used
instead of the LT1963, it must meet the following requirements:
•
•
•

Passive Filtering

To achieve the necessary isolation from high-frequency power supply noise, passive filter
networks are required on the power supply pins. The topology of these ferrite bead circuits
is given in
RocketIO™ X Transceiver User Guide
UG035 (v1.5) November 22, 2004
Texas Instruments TPS786xx 1.5A RF LDO (For more information about this device, visit
http://focus.ti.com/docs/prod/productfolder.jhtml?genericPartNumber=TPS78618.)
Figure 4-21 shows the schematic for the adjustable version of the LT1963
4
OUT
3
GND
+
TAB
1µF
330µF
93.8Ω
Must be a linear regulator.
Must have output noise no greater than 40 µV RMS from 10 Hz to 100 kHz.
Must regulate to within 2% of the nominal output voltage (±50 mV).
Figure 4-22.
www.xilinx.com
1-800-255-7778
1µF 1µF 1µF 1µF 1µF
2.5V@1.5A
1µF 1µF 1µF 1µF
GNDA
ug035_ch4_15_022703
R
115