The manual states that the Micro Mestro can be powered from 5V to 16V input.
Also, you get 5V from USB.
I imagine this means you’re using a linear regulator with 16V max input. If the chip itself is 3.3V, then that would make it easy.
But that doesn’t quite make sense, because you also output 5V signals. With a typical linear regulator you’d get 1.2V drop-out or so, and even high-performance ULDOs that have an input range up to 16V typically have a drop-out of 0.3V or so (like the LF50AB.)
Is it actually the case that, when powering from USB or exactly 5V in on the VIN pin, the actual output on the servo control pins will be more like 4.5V?
Or is there some magic going on here?
The regulator used in the Micro Maestro is an ultra low-dropout voltage regulator. At the maximum load of 50 mA, the dropout voltage is typically about 120 mV. Since the Maestro does not operate at the limits of the regulator, the dropout voltage from that regulator should be lower. However, the voltage regulator circuit includes two diodes that drop the voltage about 400 mV. Thus, the 5V outputs are at about 4.5V when powering VIN at exactly 5V.
When the Micro Maestro is powered from USB (and assuming there is 5V being supplied), the supply voltage goes through just one diode and no regulator, and the 5V outputs are about 4.8V.
