I am having some problems while developing a new project with an Arduino 101:
When the board is powered by USB the 5V-Rail has exactly 5V. If I power up with the DC jack or via VIN the 5V-Rail will rise to 5.27V (in my case) and the attached CAN-Bus shield (with a MCP2515 - Voltage limit 5.2V) is not working on the CAN-Bus side (SPI is still functional, but not the RX/TX of the CAN-Bus connection). Going back to USB power everything is fine.
So I wonder why the board is set to +5% on external power? Looking into the datasheet of the used DC/DC (Ti TPS62153) with fixed 5V there is an option to set exactly these +5% output voltage via a DEF pin (DEF, Output Voltage Scaling (Low = nominal, High = nominal + 5%)). R70 will provide this High input signal to the DC/DC and when removed the board has the 5V I think would be normal.
Why the design with +5% (to at least 5.25V) was done? You see some components will not work - even with an out of spec voltage of ~0.05V!
It's unusual that other components won't work when the supply voltage is only 5% high. Have you checked to see if the shield is getting power when you switch to the DC Jack (check the supply buss on your shield with a voltmeter and the main board connected to power both ways)? It sound's almost like no power is being delivered to the shield. I would still go ahead and make the adjustment (if that's possible) to get the voltage at 5.0 Volts just to be safe. No idea why it would be set high, but 5% isn't much. When you're on the USB, there's another regulator doing the job which is the reason the voltage is different.
Sorry, but I double checked the voltages before posting here! The DC/DC will deliver 5.27V when powered by DC jack or VIN. There are no current limits that would count - the laboratory supply Rhode&Schwarz HM-7042 that can provide at least 2 Amps - super smooth Voltages checked with Agilent U1253B to the fourth digit... As an R&D engineer I know how to use those tools!
MicroChip clearly states 5.2V as absolute max. rating for the MCP2515 and all boards around here have 5.0V (Okay slightly lower as 4.98V or so).
But why is the Arduino 101 configured for 5.25V? - this is the question?
Maybe some of the dev. team can answer the question - THX!
Voltages checked with Agilent U1253B to the fourth digit... As an R&D engineer I know how to use those tools!