Hardware Insights Forum

Yes, for all their infamy, there is something good about the SMOOTH family of chips manufactured by STMicroelectronics. I'd consider them innovative, even. Too bad they were the ones who came up with it.

The datasheet for the L7250 says:

STMicroelectronics wrote:The spindle system includes integrated power FETs which are driven using ST’s Smoothdrive pseudo-sinusoidal commutation technology.

I'll take their word for it. I just did a quick comparison of two ST340014As, one with SH6950D and the other with SMOOTH 100244097. The one with the SMOOTH chip really does emit much less whine. So if silence is the priority, the ones with SMOOTH chips are actually the ones to get. This also explains why those Western Digital drives (which always use SMOOTH chips) are so, so quiet.

OK, as it turns out, they're not an invention at all — and therefore shouldn't have been patented to begin with. Each phase output (all HDD spindle motors are 3-phase) is a miniature Class-D amplifier (their inputs being simple sine waves of the desired amplitude and frequency — and with each phase 120° apart just as in 3-phase mains power — and the output filters are omitted, as they're not needed given the motor's own inductance). I hate it when companies abuse patent laws for their own profits at the expense of their competitors.