Thomas Hornschuh

Papilio Pro 3.3V rail max current

5 posts in this topic

Hi,

I'm currently conneting an ESP8266 WiFi module to the Papilo Pro. I tried to find a specification about the max. current the 3,3V rail can deliver. According to the data sheet of the LTC3419 converter it can deliver 600mA.

My measurements show that the ESP8266 draws around 190mA average current.  I'm aware that also the USB port itself is limited, but this is not my question at the moment. 

I think the SPARTAN-& draws most of its current at the 1,2V rail, so the 3,3V rail must power the other chips (SDRAM, Flash, FTDI), so I think the addtional 200mA is ok.

 

Thomas
 

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I think you would probably be ok (although the ESP8266 draws current of >300mA when transmitting). If it was me though, I'd put it on a separate supply so as not to worry, plus the bursty current draw of the esp8266 doesn't always play nicely with marginal supplies.

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My concern is not so much the stability of the ESP8266 I just woud like to get some information (preferably from Jack) about the power budget left for wings on the 3,3V rail.

According do the datasheet ESP draws about 180mA when sending (in 802.11b mode, in newer modes it is even less). My measurements confirm that. If there are very short peaks with more is possible, but this may influence stability but no damage the switch regulators. 

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I have powered ESP8266 using PPro rails just fine, even when overclocked. Just make sure you have a nice caps on ESP supply to support the high current bursts.

On another note: I have ESP8266 wings ready, in case you want them. I can sell you the PCBs for USD1.5 each, plus shipping. Or I can share design with you if you want to build them yourself.

Alvie

esp8266wing-img1.jpg

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Hello Thomas,

It sounds like you have a good handle on most of the details already. The voltage regulator can provide up to 600mA but a computer will only provide 500mA. If you need the full 600mA then connect through a powered USB hub. The esp8266 will burst up to 300mA when starting but uses much less when running. 

The piece of the puzzle you are missing is how much the FPGA will use, but unfortunately I cannot give you an easy answer to that. It is highly dependent on the design that you are running on it. There is an excel spreadsheet you can download from Xilinx that will look at your design and tell you what kind of power it will use... It can be super low, when I ran the XPower? spreadsheet on the OLS design when we were running it the estimate was only 10-20mA so we ended up using a 50mA voltage regulator in that design. It never had any power issues which validates that very low power usage for that application... Or it can be pretty high, just depending on your logic...

The easiest way to tell for sure is to buy one of these Charger Doctors from ebay. Plug your Papilio into power through it with just your app running and see what the current draw is. Then do the same with esp8266 connected and you should have a very good, real world picture.

Jack.

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