Feature #3313

design simple SFP experimentation board

Added by laforge 2 months ago. Updated 15 days ago.

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Let's design a small SFP experimentation board consisting of
  • SFP cage + connector
  • 4x SMA for RD+/RD-/TD+/TD-
  • 2.54mm header for accessing I2C of SFP
  • 2.54mm header with all the misc signals (LOS, etc.)
  • power supply (5V input, DC/DC to 3.3V, 300mA max, filtering as per SFP MSA)

Basically we want the inverse of

There seems to be a board close to what we want, but USD 495 is ridiculous for something that has a parts cost of USD 30:

The resulting design should be something small which we can easily hand to prototype manufacturers. Staying within 10x10cm might be a good idea, if possible.

In terms of the SFP connector and cage, I would suggest to use
sfp.lbr sfp.lbr 20.6 KB SFP footprint / symbol tnt, 06/05/2018 11:32 AM

Related issues

Precedes Misc Hardware Projects - Feature #3314: design simple SFP experimentation board with LVDS transceiverIn Progress2018-06-042018-06-04


#1 Updated by laforge 2 months ago

  • Precedes Feature #3314: design simple SFP experimentation board with LVDS transceiver added

#2 Updated by tnt 2 months ago

I just did a footprint for SFP cage and connectors referenced above. I'll upload it this afternoon (couple of tweaks left :p)

#3 Updated by tnt 2 months ago

  • Checklist item SFP part footprints library set to Done
  • File sfp.lbr sfp.lbr added

Added eagle SFP cage and connector. Could use a double check of course :p

#4 Updated by laforge 2 months ago

mschramm please let's keep the related eagle library / design files in @osmo-small-hardware.git and make sure to commit frequently. thanks!

#5 Updated by mschramm 2 months ago

  • Status changed from New to In Progress

#6 Updated by mschramm about 2 months ago

  • Checklist item schematics set to Done
  • Checklist item board layout set to Done

#7 Updated by mschramm about 2 months ago

  • % Done changed from 0 to 50

A simple PCB has been committed, derived mainly from SFP exoperimenter PCB (see #3313).

Remarks see ticket #3313, some apply here too. - The break in the GND plane under the diff signals of the SFP receptacle is not nice and should be improved on both PCB - if we don't go to a 4-layer PCB (and remain w/ 1.55mm FR4) for a 'closer' GND plane.

#8 Updated by laforge 17 days ago

13:25 < tnt> Any "real" design using the SFP would be 4 layer, so I guess it's an argument
             to make the experimentation board as close to what a final product would use.

so let's go four-layer. mschramm: please change layer stack-up, add gnd/vcc planes, and adjust trace widths for "usual" four-layer stacking.

#9 Updated by laforge 17 days ago

let's please also add some form of polarity protection to the DC input. A regular series diode would be the simplest approach, but the TLV1117 requires up to 1.4V drop-out voltage, which makes the budget for 0.7V quite tight. (3.3+1.4=4.7V). Even a shottky diode is unrealistic at that point.

So either we use a different approach for polarity protection, or a different voltage regulator with lower drop-out voltage. Moving away from nominal 5V DC as input voltage is not really a good idea, IMHO.

There are LDOs with built-in reverse polarity protection. However, we cannot use electrolytic caps at the input (C3) in this case. But 10uF at 5V is definitely possible to get as ceramic?

#10 Updated by laforge 17 days ago

MCP1825ST-3302E would have a maximum drop-out voltage of 0.35V, i.e. allow a series diode. It's readily available and we have used it before (and hence it's in our eagle lib). maybe worth a thought?

#11 Updated by tnt 17 days ago

SFP+ allows up to 450 mA current to be used by the module.

#12 Updated by tnt 17 days ago

nm ... I misread the datasheet of that chip, it can do 500 mA ...

#13 Updated by laforge 15 days ago

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