[TriEmbed] another fan motor driver chip: Microchip MTD6501G-HC1

[Pete Soper]

http://datasheet.octopart.com/MTD6501G-HC1-Microchip-datasheet-11052439.pdf

I found it readingthis 
<http://www.elektor-labs.com/project/high-end-propeller-clock-120732.12550.html>. 
After reading wads and wads (but interesting wads) of stuff about this 
POV design I got to this:

" I've assembled the propeller on the motor's hub for the first time, 
but it's a disappointing experience. With no load, motor runs very 
smoothly without any noise, but with the propeller, it does not manage 
to start. Sensorless brushless motors have a particuliar startup 
procedure which fails with the MTD6501. I guess the "locked rotor 
protection" activates because of the high inertia moment of the rotating 
assembly. I tried to fool the controller by adding a few ohms on motor's 
wires but it doesn't solve the problem."

But this guy's drive motor runs at five volts and may likely be from a 
2.5 inch drive. I can confirm that hitting a 3.5" drive motor with 12 
volts will swing a one pound mass, so the technical hazard with this 
chip with a 12v motor is the same as with the TI and Philips chip: false 
triggering of the "something is blocking the fan blade" detection 
because of the low acceleration going along with high mass.

This is the kind of thing you'd put between a simple RC controller's PWM 
output and the disk drive spindle motor. Notice you don't need a 
controller to run the motor at "full speed" with this chip, as this can 
be done by tying the PWM input high.

One might ask himself/herself whether the .8 ampere limit of this chip 
is adequate. Looking at a 2001 Fujitsu blurb about their super high 
performance 15k rpm SCSI 3.5" drive and it's total power consumption of 
11 watts, I think the answer for a drive made in the past half dozen 
years is yes (and "heck yes" for a 2.5 inch, five volt drive). The 
largest version of this chip is an eight pin SOIC ($1.09 at quantity 10 
from Digikey) but it would be trivial to solder dead bug style and set 
up with a little piece of aluminum bar stock or something stuck to the 
thermal pad for prototyping. Hmm, another idea would be to bend the pins 
down slightly, solder a long but narrow strip of copper or brass foil to 
the thermal pad, then solder the SOIC chip to a regular breakout board 
<http://www.adafruit.com/products/1212>. It might be that this chip 
stays relatively cool: my situation involves worst case currents and 
duty cycles.

Also, to clarify, the Arduino servo library would just be to arrange an 
appropriate PWM signal to a circuit like the chip above. That's overkill 
for this chip.  The PWM you get out of the analogWrite command for 
supported pins would work (but not for the TI without using 
setPwmFrequency: it's minimum PWM frequency is 15khz. That's hugely 
faster than what comes out of analogWrite by default). No way, no how 
can the disk drive spindle motor be made to move back and forth and hold 
a position like a typical servo motor you see in a model airplane (well, 
actually it can, but not with the servo library and a driver chip 
anything like the ones discussed, and for only six positions).

-Pete

PS Are these reams of verbiage hitting your mailbox annoying you? If you 
have a smartphone this might constitute Guantanamo-style torture. If you 
follow the link below to the email listinfo you can go into your 
subscription settings and turn on digest mode to get all the mail for 
the list just once a day. If that isn't good enough but you want to read 
this stuff at the time of your choosing just set "nomail" and browse the 
email archive. (If you don't remember your password I can do it for you, 
but a reminder will go out August 1st)


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.triembed.org/pipermail/triembed_triembed.org/attachments/20140724/e3cf7d86/attachment.htm>