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I am currently laying out a PCB where there is a TF CARD on it. The schematic is as below. I have this capacitor to place which I suppose might be a decoupling by pass capacitor, so unless my mistake I have to put it close to the power pin which might be VCC. However we have a connector for this TF card and the connector of the VCC pin is just below the connector/slot so I can not place the cap directly close to the pin. What woudl you recommend : 1./ Put the cap on the same layer on the edge of the connector ? 2./ Put the cap on the other side of the PCB and create a via ?

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For bulk decoupling of a SD card, I'd just put it on the same side, near the edge of the connector. Sure, you can do the math to figure out which path has more inductance/impedance -- backside + via, or top-side + some copper, but I don't think it's going to matter very much since this isn't a UHS-II / ultra-high-speed card from what looking up a TF Card was. If you have power planes, that will be your high-speed source of charge anyway.

Assumedly you're feeding this VCC from a power plane on your board anyway, so I would just place the bulk on the same side as the connector and give that cap its own vias to the power plane. Offhand I'd suggest a 0.1uF close to the pins, and then 1uF or 4.7uF somewhere close by -- caps are cheap, can't hurt (assuming you're not BOM cost sensitive).

EDIT: It's also not a bad idea to place a 0R series resistor right on the MISO pin of the connector, in case you need to add some termination in the future.

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  • \$\begingroup\$ No problem -- I also added a comment that you may want to think about placing a 0R series resistor on the MISO pin of the connector, in case you need to tame a fast driver. \$\endgroup\$ – Krunal Desai Jun 6 '16 at 20:33
  • \$\begingroup\$ The 0R woudl be placed between what and what ? \$\endgroup\$ – chris Jun 6 '16 at 20:36
  • \$\begingroup\$ Connector MISO Pin -> 0R -> SPI_MISO0 \$\endgroup\$ – Krunal Desai Jun 6 '16 at 20:52

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