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The ADC3681 recommends using ferrite beads on the outputs of LDO used to provide the AVDD and IOVDD supplies as shown in Figure 9-8 of the data sheet. Is there a recommended bead or spec for the bead that should be followed?
The eval board uses switchers for these voltages with a large Murata bead/filter on the outputs, while other LDOs on the board that power clocking and input amplifier use a simpler 120 ohm (@100 MHz) bead. Would this 120 ohm bead work for the AVDD LDO output?
Hi Mark,
Yes, the ferrite bead in the bill of materials for the EVM is what we would recommend. I am sure there are other suitable subs that other vendors may offer.
Keep in mind, when using a ferrite bead, or additional filtering on the power supply rails, that you may need to up the voltage a bit to overcome any loss of the ferrite bead, etc.
For example, if the AVDD rail is 1.8V, you may set the output of the LDO to 1.9V.
Regards,
Rob