I'm trying to design a custom board that will include the FGPMMOPA6H GPS.

Looking at the Adafruit integration of this GPS, I can see a ferrite bead on the output of the LDO (MIC5225-3.3). See below:


I agree with the use of an LDO to get a clean power supply for the GPS, but I don't know how to choose a "good" ferrite bead on its output.

I'm not very familiar with the use of ferrite beads, so a little help would be highly appreciated!

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    \$\begingroup\$ You won't need the ferrite bead if you find a LDO with low enough ripple. The requirement for FGPMMOPA6H is max 25mVpp according to the datasheet. \$\endgroup\$ – Peter Karlsen May 14 '20 at 9:36
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    \$\begingroup\$ There isn't a good way to determine the FB requirements for the circuit in your question because there is no specification for what the ferrite bead is intended to do. This post might help understanding. Also this one. \$\endgroup\$ – Andy aka May 14 '20 at 9:59
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    \$\begingroup\$ @PeterKarlsen Beads will not help with ripple, even a bulky Murata BNX025H has its first zero at 2MHz. They are only really useful for switching noise and EMI, so I would place one between PSU and LDO on the VIN-side. \$\endgroup\$ – Andreas May 14 '20 at 10:00
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    \$\begingroup\$ @Andreas You are right. I woudn't use a ferrite bead at all. The ferrite bead probably originates from the FGPMMOPA6H reference design in the datasheet, where the source of supply is unknown. It is most likely just copy/pasted by adafruit. The bead serves no purpose where it's placed. It would be better to put it on VIN of remove it completely. \$\endgroup\$ – Peter Karlsen May 14 '20 at 10:16
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    \$\begingroup\$ A low drop out (linear) regulator doesn't produce ripple itself. A ferrite bead seems out of place in that circuit. \$\endgroup\$ – JRE May 14 '20 at 11:55

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