[NASR1]

HI

LS7290 STEPPER MOTOR CONTROLLER

80V 7A Drive

LS7290 Controls Bipolar and Unipolar Motors

Full, 1/2, 1/4, 1/8, 1/16, 1/32,

PCB & Sch whit protel.

[lumberjack_jeff]

cool stuff! Bookmarking.

[mura]

It is not so good.

http://www.lsicsi.com/StepperDrivers.htm

[NASR1]

It is not so good.

http://www.lsicsi.com/StepperDrivers.htm

Dear Mr. i use this Driver six months for my cnc. Until now not encounter the problem. Please tell me what the future this problem will have consequences thanks.

[H500]

The design appears to use open loop pwm without current feedback. The microstepping likely won't be even. How well does it working?

[Mariss Freimanis]

I don't know why it's called a unipolar drive when the schematic shows a dual full-bridge design. The low voltage regulator design is a little lame (could be done without a zener diode reference) but that's all I can criticize about it.

Mariss

[beliefdrive]

to Mariss
ls7290.pdf‎ this file is unipolar driver schematic
i thinks bipolar in develop

[irving2008]

The design appears to use open loop pwm without current feedback. The microstepping likely won't be even. How well does it working?

I investigated this chip as a replacement for the 297 becuase of the microstepping but simply put the current control simply doesnt work except in full and 1/2 step. If you want to use the other stepping modes you need to do the sense voltage comparison and externally. As it says in the datasheet:

"Peak current feedback control using pulse width modulation chopping can only be used in full-step or half-step modes..... In all other
modes, the VREF input should be set to VDD and the sense inputs should
be grounded."

When i spoke to LSI on this they explained its because the blanking time from the monostable is too long except in 1/2 and full step operation.

[H500]

When i spoke to LSI on this they explained its because the blanking time from the monostable is too long except in 1/2 and full step operation.

Sounds like another chip with a built-in design error.

[irving2008]

Sounds like another chip with a built-in design error.

Well unlike the Allegro chip with a similar problem, LSI are quite candid about this... the LS7290 is a replacement functionally for the 297 in 1/2 and full step modes only but the internal logic wont provide current feedback for other modes and they suggest using external sense components or reducing supply voltage as appropriate.

Here is the relevant info from the tech note:

Duty Cycles of active-low Outputs, INH1/ & INH2/:


The duty cycles of INH1/ and INH2/ outputs are fixed per table 2 of the LS7290 datasheet.

The SENSE1 and SENSE2 inputs are provided for over-current protection only, not for chopping control of the drive outputs.

In any stepping mode other than the full-step and the half-step modes, if the inhibit outputs are truncated due to the SENSE inputs reaching the VREF level, the fixed duty cycle ratios of the INH1/ and the INH2/ will be disrupted leading to motor misstep.

Therefore, in modes other than the full-step and half-step, the SENSE1 and SENSE2 inputs should be tied to ground and the VREF input should be tied to the positive rail. Under these circumstances, if over-current becomes an issue, it can only be resolved by lowering the motor supply voltage.

In the full-step and the half-step modes however, since the fixed duty cycle ratios for the two inhibit outputs are 100%-0% and 70.7%-70.7%, the SENSE inputs can be utilized for chopping the INH1/ and INH2/ outputs, without disrupting the duty cycle ratio. Therefore, in full and half step modes SENSE input chopping can be used for motor current regulation.

When the SENSE inputs are used for output chopping, the INH1/ and the INH2/ outputs are terminated (switched low) when the corresponding SENSE input becomes equal to the VREF. The maximum voltage at VREF= 3V, when chopping is used.

For fixed PWM, the duty cycles in table2 are adjusted within a 32us window based on 8MHz clock. For reference, this will translate to 22.6us on and 9.4us off for a 70.7% duty cycle.

[boldive]

LS7290 is a good replacement for L297. There is no microstep. It is in datasheet, but it useless. Wait for the LS8290/LS8291
They support microstep, slow/fast/mixed decay modes. I am working on the schematic and PCB design now. I hope it will be done soon.

P.S. It was nice to see my schematic for bipolar drive on LS7290 taken from other forum in the first post.

[Mariss Freimanis]

irving2008,

This is a common occurrence with IC manufacturers. They are silicon IC design and manufacturing experts but not application experts. Here's how it works:

Company X gets a contract to design an application specific IC. The customer that contracts Company X has a very specific and narrow requirement that meets their need; an example might be a step motor driver IC for a particular motor that will go into a particular ink-jet printer.

Their contracted need is for a bazillion motor ICs that will go into a bazillion printers to be marketed in 2001. The ICs work as expected and a bazillion printers are sold. They are never seen again after 2002. To help defray the ASIC costs, the printer manufacturer releases the rights for Company X to market this IC to anyone after 2002. The printer manufacturer won't need them after 2001 so it's a safe bet.

Company X puts their own part number on the motor IC and markets it to all comers in 2002. It costs them nothing in design or development because someone else already paid for it. They draw up datasheets, set a price schedule and put the part in their stable of available IC devices.

You look at the datasheet, it is 10 pages long, and the part seems to be OK. You buy it, try it, and you find there are some esoteric details that make the part problematic in your design. Kind of like the unusual current blanking time for instance. Company X is a reputable good guy, they come up with application notes that delineate the shortcomings of this particular detail and explain how it's designed in and cannot be overcome.

You are a reputable good guy yourself. You start searching through application notes only after you have a design problem. That's reasonable; how can you look for a solution to a problem before you know you have one? You have to invest time and money to reveal a problem exists with an IC. Then you go to app notes.:-)

Who is to blame? Lots of choices but in the end, in large part you are. Company X put up the product you bought and had the app-notes that explained why their product may not be perfect for you. You on the other hand expected to have Company X to give you what you wanted without you having to do the work necessary to get what you want. Their IC is what it is; they are not obligated to make it what you want.

This is the crux of it. If you want something to meet your needs then you have to do it the hard way; design it yourself. Company X is not obligated to do it for you and they won't.

You have every resource at your disposal today. CPLDs are tools to design what you want your way and they are marvelous. You don't need to depend on Allegro or SGS Thompson to give you what you want. Make it yourself; it will work better.

Mariss

[irving2008]

Mariss,

I am inclined to agree with you on the 'make it yourself front', and I usually do so where it makes sense - at least that way you know exactly how it works. Having said that, I also recognise that some people have limitations on skills, budget and/or time (in my case its usually the latter two) and would like to find some of the more difficult bits 'done for them'. Hence when a chip comes along that seems to offer good things people jump on it... not always understanding the limitations. Although to be fair to LSI they did make this limitation clear in the data sheet and the app note so no one should have gone ahead and invested time without understanding the limitation. The main and only advantage of the LS7290 over the L297 in the majority of systems is simply price.

[mrgadgeteer]

Can someone suggest a decent open source design that will run unipolar motors using Mach3 or equivalent software? I've been tinkering with IRF540 MOSFETs switched by my BS2 and a Slo-Syn M063-FD09 with little success. They drive little scanner size pancake motors perfectly fine but when the heftier Slo-Syn is attached the 540's appear to stay "on". A very slight pulse does get to the motor. I'm using regulated 12V and current limited to roughly 2 amps by a light bulb on the motor side. This motor wants almost 5 Amps but I'm afraid to push to the 540's envelope just yet.

I only have a basic understanding based on my own "trial & error hacking" so it's not difficult for my eyes to glaze over with all the the techno intricacies, design errors etc. discussed. This is fun but confusing, I sure could use a mentor!

Thanks
Mike

[H500]

Can someone suggest a decent open source design that will run unipolar motors using Mach3 or equivalent software?

See post 116 here:
http://cnczone.com/forums/showthread...=81125&page=10