Converting 0.6V 20A DC to AC (frequency ~ 240 Hz)
Let go of the 5V -&gt; 0.6V DC/DC idea and design an inverter based on a H-Bridge (or many H-Bridges) feeding a transformer (many transformers).
You could then let the inversion step also involve the voltage conversion step (which is a good idea, because DC/DC voltage conversion is harder than AC/AC, which can be done trivially with a transformer).
Also, 5V 4A is a lot of power for such a low supply voltage - I'd recommend you don't go that low. A thrown out laptop power supply typically delivers around 20 V. Working down from a higher voltage is easier, here, because you get more &quot;headroom&quot; for regulation.
Then: I have no idea what a &quot;linear resonant actuator&quot; is, but it darn much sounds like what a speaker does.
So, idea: that &quot;H-Bridge feeding into a transformer design&quot; is something you shouldn't be designing yourself. That's just a class-D amplifier in the end, using the properties of a transformer instead of output inductors to do the lowpass filtering / smoothing of the output voltage. So, class D-amplifier, use a higher input voltage than 5V, use an appropriate transformer to convert down to your desired AC voltage. Feed whatever sine waveform you can generate into the amplifier, calibrate output amplitude once.
If you want the AC amplitude at your actuators to be very exact, you can pick an amplifier with external feedback. I doubt you'll need it.
In fact, if your class-D amplifier is beefy enough, you don't need the transformer at all – and can directly work with sufficiently sized inductors as you'll find in the application circuits in your amplifier's datasheet. I find the transformer alternative nice, because it shifts the cost from a lot of low-resistance semiconductor switches to a simple relatively low-power transformer.