Mystery PWM chip???

Another hint that should narrow down the search significantly.

Ground pins are in the middle of the chip at 6,7,8,17,18,19.

I don't think you're going to find an IR device fitting that bill. They don't tend to use large pin-count narrow smd packaging, and they don't make a point of marketing actual controllers - despite the CIC designation applied to their range of drivers.

At 24 pins, it could be a motor controller from Allegro, with ground-sensed functions bypassed, a serially addressed driver controlled by an external intelligence or, get this, a TI-Unitrode SCSI terminator(?). Unitrode didn't tend to go overboard on the ground pins, mostly because they knew what they were doing.

As this part is apparently adequately buffered, there would be little point in including the ground grouping for heatsinking, unless it was a normally freestanding low voltage power controller, being used for its logic features alone. I'd scout for stand-alone h-bridge circuits, or even audio controllers.

RL

I don't have an answer. But this got me thinking: Are there any search tools online that allow one to fill in details such as known pin functions, supply voltages, etc.?

The Newark and Mouser et al filters sort of do this, but you have to know exactly what class of device you are starting with. It also has to be something they stock and current production.

The Allegro 2919 does seem to be a possible starting point. Its grounds are 6,7,18, and 19, and a logic ground can be needed on 8 and 17.

Next step would be seeing if the inputs and outputs align. And what else Allegro has to offer.

The Allegro A3992 seems to match six odd ground pins, one odd vcc pin, and an oscillator input on a narrow DIP24.

Seems by far the best candidate to date.