> > > This means that a reset circuit operating from the only externally > regulated 5 V input with a 4.4 V threshold voltage is likely to > experience resets when connecting USB devices. > > The current reset IC you're using is APX803-44SAG, right? http://www.diodes.com/datasheets/APX803.pdf Its reset threshold: min. 4.31V typ. 4.38V max. 4.45V If using a 4.0V APX803-40SAG, then becomes min. 3.94V typ. 4.00V max. 4.06V
> If we stick with the idea of monitoring only a single input, which > would then have to be the 5 V rail, I would recommend using a reset > chip with a threshold voltage of 4.0 V. This will still let the > regulator of the 3.3 V rail produce a 3.0 V output under worst-case > conditions, while providing a safety margin for USB devices with > high inrush current and for power supplies providing a low "5 V" > voltage. > > These experiments should be confirmed with other power supplies, > including an official M1 power supply. > yes, needs to be confirmed when replacing a 4.0V one later. -Adam
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