IC7 controls two things.1) The pin 13 LED2) The FET T1T1 controls the connection between the usb power bus and the 5v bus on the main board. If Vin is less than 6.6v, the usb and the main power bus are connected to power the Arduino from usb power.The Mega2560 has problems when powered by the Vin (barrel jack) and the usb simultaneously. If you had your Mega connected to usb and external power applied to Vin, it could have damaged the board. Read this topic about that:http://arduino.cc/forum/index.php/topic,82046.0.html
My bad. I understood that problem to include a voltage less than 6.6v applied to Vin also. If that is not the case, you have my apology.Well supplying Vin at less then 6.6v while also plugged into USB is operating outside of the boards stated specifications and requirements for the board, and indeed could cause problems. But your 'warning, danger, danger' did not couch it to this specific case but rather stated a global " has problems when powered by the Vin (barrel jack) and the usb simultaneously." which is not the case when supplied with proper Vin voltage clearly stated.edit: Since you put your response to me so eloquently, I thought you might have forgotten to mention to the OP why IC7 would get hot.I don't have a clue. IC7 is an op-amp and should not ever run hot unless it's defective or something on it's output pins is shorted to ground or Vcc. As the normal board current runs at less then 100ma, something inside or wired to IC7 is drawing 200+ ma of current that it should not be. Maybe the mosfet switch has a shorted gate and is applying +5vdc back to the op-amp's output pin. It could be troubleshoot with the proper methods and test equipment, but via a internet forum not so easy.Lefty
The Mega2560 has problems when powered by the Vin (barrel jack) and the usb simultaneously. If you had your Mega connected to usb and external power applied to Vin, it could have damaged the board.
Quote from: SurferTim on Dec 05, 2012, 01:01 pmThe Mega2560 has problems when powered by the Vin (barrel jack) and the usb simultaneously. If you had your Mega connected to usb and external power applied to Vin, it could have damaged the board.I usually don't quote myself, but I do not see this as "WARNING DANGER DANGER". I always like your input tho. Sometimes in my haste, I forget a detail that could be important.
@retrolefty: Now that I seem to have your attention on this, do you see a problem with IC7 if Vin > 10v? That would effectively overdrive the Vin input to IC7, would it not? Could that cause a latchup condition on the output?Just trying to figure out why it gets hot.
Input Voltage (limits) 6-20V
Datasheet.http://www.ti.com/lit/ds/symlink/lmv358.pdfMax voltage any input = 5.5vThat means 11v is the upper limit to Vin without overdriving the op-amp.
Maximum Input Current 10 mA
I like your datasheet better. This is what I was concerned about, and it is mentioned as one of the main features:No Output Phase?Reversal from Overdriven InputSounds like it is on its way to "transistor heaven"?
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