RE: [CAD_CAM_EDM_DRO] LMD18245, Gecko MULTIPLIER, and SLA7062 Sync Mode

Hi John,

You're talking about pin 14, the DAC reference?

I was hoping to add reduced current holding to the PIC on the EAS boards,
but it looks like the PIC is out of pins!

As I mentioned in a previous post, I'm considering running the four EAS
microstep boards from a single oscillator, so perhaps I should figure out a
PIC to watch the step lines, and reduce the reference voltage to the 8
LMD18245's when they are not stepping. I'll want to add control of a SSS
module for spindle control; motor "standby" could even be controlled by a
simple additional controlled circuit.

The EAS opto isolator board (rev4) might be enough to run the SSS and
control the DAC references? I know it buffers input lines as well as output
lines.

If the SLA7062 has a "weak" problem in stopping on non-halfstep positions
(did I get that right?), then what would appear to be needed is a "STEP
PULSE MULTIPLIER" as used on the Gecko G210 (A) drivers.

Dave M. is saying that microsteps past 1/2 step won't guarantee sufficient
holding torque. The step pulse multiplier in the G210 solves this from what
I can understand. The 1/2 step remains "coordinated" with the internal
microstep.

Perhaps the SLA7062 needs a little external "sync help"?

Gotta LOVE those Geckos!


Alan KM6VV

> Hi,
>
> I'm also a bit confused by the SLA7062 data sheet. All they say is that
> noise is reduced when the unit enters sync mode. It doesn't really say
> what
> sync mode does.
>
> The way I reduce current in the ELS driver which uses LMD18245 is by
> shifting the reference voltage from 5 volts to something like 1.25V. This
> causes the motor current sensing circuits to start chopping at 0.75A
> instead
> of 3A (when configured for full drive current).
>
> The side effect of this is that the motor now becomes quite a bit noisier
> since the chopping happens differently from the full power mode. The
> LMD18245 is also a 'fixed off time' chopper.
>
> The only other way to reduce current would be to change the current
> through
> the individual windings to perhaps reduce one winding to 0 current and the
> other to some low level that causes less noise. However, when I tried
> that,
> (before using the 'reducing the reference voltage' approach), I found the
> motor always moved so I gave that up.
>
> John Dammeyer
>