Alright! It looks like it's a go (see previous log).

Briefly-recapped, I've a Class-D Audio Amplifier chip that I wanted to try out as a DC Motor Driver. Why not, eh?

Finally finished the PCB-etching and soldering process, and It Works! ish.

There seems to be a weird glitch where the Mute/Standby pin is getting triggered randomly. I can see it with a 'scope, so it must be shoddy wiring somewhere.

Otherwise, as ridiculous as it is, (a lot of pins, a lot of R/C circuits, weird-value higher-than-my-normal-voltage caps, dual-supply, analog inputs, nevermind being designed as an *audio* amplifier...) it seems to be a fine motor-driver.

Some oddities: While 120mA max quiescent current (for the entire chip) doesn't sound like much when talking about switching 4Amps on each channel, remember it's running at (up to) +/- 25V. The docs aren't particularly clear about where that Q-Current is coming from, nor going, but we might be talking upwards of 2-3W (!?), without a load.

Then there's three built-in voltage-regulators "for internal use" at +5V, -5V, and 10V... I chose to tap off the +/-5V to drive a couple potentiometer-voltage-dividers as a DC input for speed/direction testing... Tried to limit them a bit, but had a limited supply of suitable pots, and the input-resistance is a mere 30kohms, so I'm drawing around 15mA on each pot, through what might well be *linear* voltage-regulators, dropping down to 10V from up to 50V... that might dissipate a bit of heat, too.

Anyways, suffice to say, even with a motor running at a measly 150mA at maximum-output (and even when the output is at 50% duty-cycle = no motor movement) the chip is producing a bit of heat. OTOH, stalling the motor bumps it up to about 1.5A, and with some quick-tests that hasn't seemed to cause a noticeable heat-increase...

At first I thought it had to do with all-that switching (200kHz, 50% duty-cycle = off)... The ringing at the edges is *gigantic* (nearly double the supply voltage). Looked into the recommended L/C filters for audio-amps, but all the info I've found so far suggests that the filter doesn't actually reduce the loading on the driver (and may actually increase it?)... (see TI app-notes: sloa023, and sloa119b). And, really, direct-connection of a DC-motor to a high-frequency switching (PWM) H-bridge is pretty common, in my experience... And here we're talking *much higher* frequencies than I'm used to (with the same sorts of motors), so the inductance in the motor should be even better-suited for this, right? (TODO: what was that project, here on .io, where the guy had tiny robot with a DC-motor that didn't have enough inductance, so he added series inductors?). Anyways, I didn't bother with L/C, but did try a series-inductor just to see what'd happen, the result at the chip's output was little change. The output of the inductor, though, of course made for a much more "analog" voltage going into the motor... which I guess has the effect of essentially showing what the voltage would look like somewhere inside the motor-windings, if it didn't have a series-inductor.

Anyways, scrapped the output-filters, added a clip-on heatsink with thermal-paste and it seems fine.

That was a much longer update than I'd planned... I'll throw up some pics and stuff later.