What you are looking for is called an off-line power supply. A quick search reveals the Fairchild Semi FSAR001. Putting in 80 - 240 Vac yields 5Vdc at 35 mA max.
There are many more around.
- it is NON-isolated!!! meaning this is not a design to put into devices that people will handle - Full Stop.
let me repeat that, this is a lethal circuit, but perfectly reasonable to use under the right conditions.
Here is a snip from page 2 of the datasheet.
This answer does not address your question concerning a chip design. Which I can answer but I'm hoping that the real problem is solved with this lead and direction.
The ground clip of your scope is connected to Earth. If anything else in your motor drive circuit is connected to Earth, this can lead to some large currents through the scope, which is noise at best, burnt fuses, traces, smoke, fire at worst.
Even if your motor drive circuit is floating, by clamping one half of the motor to Earth, you make the circuit unsymmetrical. Everything in your circuit has some capacitance to everything else in the universe, Earth being a pretty significant part of that. To change the voltage across a capacitance (such as that between any part of your circuit and Earth) some current must flow, according to:
$$ I = C \frac{dv}{dt} $$
Normally this isn't a big deal, but I'm guessing you have some relatively high voltages involved, since you have a node labeled "HV_BUS" and that's a 500V MOSFET. Normally, it's just the MTR- node that changes voltage relative to Earth significantly, and these capacitive currents are really insignificant compared to the motor currents. But when you force MTR- to be at Earth potential, now it's everything else in your circuit that's switching \$\pm500V\$ relative to Earth, and these capacitive currents are in your ground, in your control circuitry, etc.
For a simpler demonstration of problems introduced by capacitive coupling to Earth, see Why one of my multimeter shows a small voltage when only one probe is connected to AC and the other dont?
The way to work around this is to clip your scope probe to the circuit ground. If you need to measure the difference between the motor terminals, use both channels on your scope, each clipped to ground and one of the motor terminals, and use the X-Y difference function of your scope.
Or, since HV_BUS is a constant voltage from ground, you can clip your scope ground lead here only if the motor driver is floating and you are confident this won't introduce a safety hazard and just consider the voltages you measure to be negative.
Best Answer
You must use a 10:1 scope probe which is typ. 9 pf //10M which should never bother a good clock design. But in your case it may slow down the clock from load capacitance. Some Ring Osc uses string of inverters in a loop each with <1pF so putting a 9pF probe on the output adds latency from current limit. dV/dt=Ic/C
simulate this circuit – Schematic created using CircuitLab