Arduino Mega voltage regulator question

So I was looking over the schematic of the Mega from the Sparkfun provided link and was wondering what deal is with having two 5vdc regulators wired in parallel? Is it to share the heat dissipation? If so how does one know that the current will be shared at all? Why use two diffent device package options when there looks like there is room to fit two of the bigger package?

Maybe only one or the other is actually populated, giving them a manufacturing option based on device availability?

So anyone care to guess the reason behind this regulator design? There certainly had to be some thinking for this unusual arrangment.

Lefty

I believe it's an "alternate stuffing options." The PCB has footprints for both regulators (one is a DPAK, and one an SOT223), and you have your manufacturer put on whichever one is cheaper and/or easier to get and/or "better" by some other definition, at the time you have them built. The packages actually overlap on the PCB, so you never actually put both regulators on there.

The duemilanove and diecimila schematic/pcbs have the same feature.

As stated that was one possiblity reason. However the picture from Arduino Mega shows both installed and in seperate locations, so I’m still a little puzzled by this design, unless they just didn’t want a photo showing a missing regulator?

So anyone owning a Mega can you tell us if both regulator chips are installed or not?

http://arduino.cc/en/Main/ArduinoBoardMega

Lefty

The second "regulator" is the FET transistor (NDT2955 or FDN340P) for the auto power supply selector.

The second "regulator" is the FET transistor (NDT2955 or FDN340P) for the auto power supply selector.

Thanks, that makes a little more sense.

Lefty

The second (paralleled) regulator in the schematic is an alternate stuffing option. The second thing that LOOKS like a regulator on the actual board is the power-selector MOSFET.