Description; Linear Regulator Selection Criteria - Xilinx Virtex-5 RocketIO GTP User Manual

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Description

Linear Regulator Selection Criteria

The selection criteria for the linear regulator are:
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The PSRR over frequency of a linear regulator (see
current dependent. Because the PSRR of the regulator in this example has a local minimum
of rejection around 300 kHz, extra care must be taken if the sourcing power supply has
spurs or high-amplitude noise in this frequency range.
If the sourcing power supply cannot be changed or a different power supply cannot be
selected, an additional filter network between the output of the sourcing power supply
and the input of the linear regulator is required to prevent substantial noise from passing
through the linear regulator at the minimum of attenuation. Because the capacitor on the
output of the regulator is part of the regulator control loop, this capacitor not only impacts
the regulator stability but the PSSR as well.
Virtex-5 RocketIO GTP Transceiver User Guide
UG196 (v1.3) May 25, 2007
Meet or exceed the characteristics specified in the Virtex-5 Data Sheet.
The PSRR of the linear regulator must provide attenuation in a frequency range where
the sourcing power supply or regulator emits noise. Use an adjustable regulator so
that the voltage can be changed, if necessary.
Figure 10-10: PSRR over the Frequency of a Linear Regulator
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Frequency (Hz)
UG196_c10_10_100506
Figure 10-10) is temperature and load-
Providing Power
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