SFP power supply specs

[Alex Eisenhut]

Hello,
I am reading this spec

ftp://ftp.seagate.com/sff/INF-8074.PDF

which I got through wikipedia.

How do I interpret this
"VccR and VccT are the receiver and transmitter power supplies. They are defined as 3.3V ±5% at the SFP connector pin. Maximum supply current is 300 mA."

but

"VccR and VccT may be internally connected within the SFP transceiver module."

So is it 300mA per pin, or 300mA all together? For my board it would be the difference between adding a linear regulator at the cage, or needing a dedicated switcher for the SFPs, especially if I add more SFPs...

I also worry about the rather slack nature of the spec, in that I'm sure the day the PCB gets built someone will find a SFP that needs 400mA per pin...

TIA!

[calmtron]

Check out some SFP datasheets. I had a quick look in one I had on hand and it specified a current consumption of 330 mA, another SFP was specced at 375 mA and some random ones on the Internet had 1.2 W or 1.5 W as max power consumption, so 300 mA per pin seems reasonable.

[Alex Eisenhut]

Yeah I'm going with 300mA per pin, it's the only interpretation that makes sense, because they don't give a ratio. Could it be 1mA for VccR and 299mA for VccR? 

Anyhow the module datasheets usually give VccT+R as a total and I've never seen it exceed 600mA, yet.