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Topic: FT232R power supply issue (Read 270 times) previous topic - next topic

JefPatat

Hi all,

My setup consists of an Arduino Pro Mini 3.3V, a SparkFun FTDI Basic Breakout - 3.3V. I have been using the breakout as power supply for a while since the pro mini + sensor remains within the spec range.

Now I would like to attach an IO expander (MCP23016) to connect a 4 digit 7 segment and I think this will be going over the max supply current (50mA) of the (see 3V3OUT on p8 of the datasheet http://www.ftdichip.com/Support/Documents/DataSheets/ICs/DS_FT232R.pdf)

I have an external power supply connected to the raw pin, supplying 5V. According to the information this PS will take over and thus the FTDI chip cannot be destroyed. But suppose I shut down my computer, disconnect the external PS and then later boot the computer forgetting about the external PS.

- The result is the FTDI will be powering and can't deliver, will I destroy it?
- How can I protect myself from this stupidity? Can I just not connect the power pin (pin 3) of the FTDI basic breakout? So all pins connected to the Arduino Pro Mini except the power pin. (I haven't dared doing this because I am not fully confident this is something I can do)

thanks in advance,
Jef

Manda

Im newbie for arduino. But i think you will need AMS117-3.3V for ext. power supply or just power ftdi with 5v and betwen tx pin on ftdi chip and rx pin on arduino add voltage divider for 5v to 3v logic. Arduino sent back 3.3v logic tx and ftdi chip can uderstan that. I dont know English enough good. But i understand you are asking about this answer.

CrossRoads

Why not power everything from 5V? Take 3.3V out of the game.
The 8 MHz promini will run from 5V without problem, and there is a jumper or solder pad to manipulate on the FTDI breakout so it's IO will be 5v also.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

JefPatat

Why not power everything from 5V? Take 3.3V out of the game.
Because I'm using an RFM12B which is 3.3V and all other components can work happily from 3.3. I just like it better with only one VCC of 3.3V, keeps things easier, no two VCCs, no level conversion.

Ok, maybe my question wasn't entirely clear. Nothing is working on 5V, I'm just attaching a 5v external power supply because that is what I have at hand and the 3.3V pro mini can be fed with 3.3 - 12 V.

Because of that I explicitely chose the 3.3 pro mini and the 3.3 ftdi breakout. I think the setup is fine.

My question is more about what will happen if the arduino + IO consume too much for the FTDI and I accidentily connect the FTDI without connecting the external power supply. Will I destroy it and how can I protect myself from doing this?

CrossRoads

Yes, you can smoke the FTDI chip if you draw too much current.
I would recommend you not connect it up and just add a 3.3V regulator to your circuit.
Example:
http://www.digikey.com/product-detail/en/SPX1117M3-L-3-3/1016-1237-5-ND/2411169
or this for a thru hole part
http://www.digikey.com/product-detail/en/LD1117V33/497-1491-5-ND/586012
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

JefPatat

I would recommend you not connect it up and just add a 3.3V regulator to your circuit.
Well, the pro mini has a 3.3 regulator that can deliver 150mA according to the schematic (MIC5205) which is enough for my purpose so I would like to use that one by providing 5V on the RAW pin.

Could you elaborate on the "not connect it up"? If I don't connect the power pin (PIN3) of the breakout it will probably work because the FTDI is fed from USB. But if the USB cable is not connected the FTDI is not powered while some pins might have a voltage connected to them (RX/TX/...) I don't know what the result is from connecting voltages to an unpowered FTDI, I keep comming back to the same question. Can these voltages damage the FTDI, can I protect it?

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