Best solution to isolate LMD18245 from uController

Leonardo

Other Parts Discussed in Thread: LMD18245, DCH010505S, REF02

Hi,

I'm planning to use LMD18245 to drive a Bipolar Stepper Motor (24V 1.8A 1.8°) with microstepping (quarter step drive with torque compensation).

Schematic that I plan to use is the same on datasheet

Below the functional block diagram reported for convenience

I have some question:

- What is the best solution to isolate Motor and Driver from micro controller? I am thinking using optocoupler with LMD18245 input but so I've to genere DAC REF from motor power supply that can be noisy when motor are running. There are better way?

- How can I use external DAC? There is only CS OUT and COMP OUT input, I need also an external comparator?

Thank you

Leonardo

over 11 years ago

0 Rick Duncan over 11 years ago

TI__Guru** 114905 points

Hi Leonardo,

A good example of isolation is shown on page 4 of http://e2e.ti.com/cfs-file.ashx/__key/communityserver-discussions-components-files/902/7180.515502_7E00_1.PDF

There is a isolated DC/DC converter U2 and two isolation devices (U4 and U5). The DC/DC would provide the DAC voltage you are looking for.

I am not sure why you need to use an external DAC or comparator. Both are built into the device. Can you explain the reason?

One final point; depending on your voltage and current needs, please look at the DRV8x devices. Awidget to aid selection is available at:

http://www.ti.com/lsds/ti/amplifiers-linear/integrated-motor-driver-products.page

You may find a device that is a better fit.

0 Leonardo over 11 years ago in reply to Rick Duncan

Prodigy 130 points

Hi Rick,

DCH010505S seem ideal but too much increases the BOM. Maybe the REF02 voltage reference IC powered from motor power supply can be a lower-cost choice?

I can use an XMega uProcessor with internal 10 bit DAC that is better than 4 bit builtin DAC and can allow more fine microstepping if requirements changes.

At this stage I can not upgrade to DRV8x devices.

Thank you

Leonardo

0 Rick Duncan over 11 years ago in reply to Leonardo

TI__Guru** 114905 points

Hi Leonardo,

Yes, assuming the current requirements are acceptable the REF02 would meet your needs at a reduced cost.

Don't you need 2 external DAC outputs for fine microstepping? And as you said the challenge will be isolating the DAC output(s) across the domains.

0 Leonardo over 11 years ago in reply to Rick Duncan

Prodigy 130 points

I will go with integrated DAC of LMD18245 and REF02 in first prototype

Thank you

Leonardo

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Best solution to isolate LMD18245 from uController