[ratep2001]

I also thought of the idea with reducing the current reference. However, in my case it simply doesn't work, because the short pulse time (i.e. blanking time of 1.8-2us) when the motor is standing still is enough to increase the current to the nominal value for spinning. Current regulation is simply lost in this case, I think some of the posts in this thread also discussed this issue.

I don't know about whether pulling the reset will help - in my case I just hardwired the Reset to Vcc and cannot change it without cutting traces on the PCB below the chip, and finding another spare output from microcontroller (can be challenging).

herdmay1, are you sure about this "feature" of A3986 i.e. pulling both reset and enable? Then I can just implement it in the next revision of the PCB, if I find the spare microcontroller outputs.

Regards,
P.

[herdmay1]

I also thought of the idea with reducing the current reference. However, in my case it simply doesn't work, because the short pulse time (i.e. blanking time of 1.8-2us) when the motor is standing still is enough to increase the current to the nominal value for spinning. Current regulation is simply lost in this case, I think some of the posts in this thread also discussed this issue.

I don't know about whether pulling the reset will help - in my case I just hardwired the Reset to Vcc and cannot change it without cutting traces on the PCB below the chip, and finding another spare output from microcontroller (can be challenging).

herdmay1, are you sure about this "feature" of A3986 i.e. pulling both reset and enable? Then I can just implement it in the next revision of the PCB, if I find the spare microcontroller outputs.

Regards,
P.

dear p,

first of all i do not subscribe to the idea that inactivity for a while renders the bootstrap caps discharged, as there always an opportunity for the lower mosfet to conduct if its is switched as it does not have a cap, and that is enough to charge the capacitor.

you kind of case occurs only in a bridge driving a dc motor which drives bridge in a particular direction where in that case the high side swithching stops as the mosfet below it doesnt get switched at all and the b'cap does not get refreshed. in normal case if your motor is running, your b'cap is suficiently large and if works fine at lower speeds your problem lies elsewhere.

also enable & reset should be sufficient once pulled down to restart.

[Matilda]

I've been playing around with this A3986 for some time now, and I'm in a love/hate relationship.
I mostly have a problem the audible noise coming from the motors.
When the motors are sitting still they hum like crazy. And that all depends on where in rotation. Sometimes one step will quite them right down.
If I set things for fast decay, they are quiet... but the motors run like 5hit.
I'm driving 5amp motors (2.5V, 0.5 ohm, 2.3mH, 400N.cm).
In my design I have an input that drops the Vreg to 0.6V (Sleep Mode), but that doesn't inpack the audible all that much.
I'm also running the system on a 48VDC power supply.

I've tried adjusting the OSC input, but that doesn't prove much.

Any new thoughts on this beast?
Has everyone dumped it?
What are we working on these days... I need something in the 5 to 7amp range.

[pminmo]

The noise change is because the percentage point of the current trip of the chopper influeces frequency of the resultant two channels of choppers beating against each other. You won't quiet it. It's the loudest chip I've tested.

[Matilda]

When my system is sitting still, basically standby or sleep mode.
Can the Enable pin of the A3986 be PWM'd?
I'm not sure if this accomplishes anything.... I read on a post that someone was sending a PWM signal to the enable pin to minimize audible noise.

Sorry about being lazy, but if I switch everything down to a 24Vdc power supply. how will things change?
Less power? More noise? Less noise?

[Matilda]

I 've been adjusting the Rosc resistor. I'm not sure if I'm out of spec, but I've got Rosc around 1.1K. This has the motors fairly quiet.
Adjusting Rosc affects: "The master oscillator period is used to derive the PWM offtime,
dead time, and blanking time."
"where ROSC, in k-ohm, is typically between 50k and 10k."

Switching down to a 24V power supply doesn't affect torque that much, in my design.
But it does make the motors a littler quieter, and not as HOT.

[Jesse B]

So from what I've gathered (not that I'd read a lot, due to this thread being 65 pages), this chip isn't very good for our application? What are some alternatives that could be used for bipolar microstepping and handle ~2.8+A RMS? Thanks

[jalessi]

Jesse,

The Toshiba TB6560HQ is a simple solution.

http://pminmo.com/toshiba-6560

Jeff...

[Jesse B]

Jesse,

The Toshiba 6560AHQ is a simple solution.

http://pminmo.com/toshiba-6560

Jeff...

I actually just found that and was reading about it. Thanks a bunch for the recommendation :cheers:

[Jesse B]

Alright so I was just looking at the parts list on the PMinMO website, and I have a pair of quick questions about the sense resistors.

First off, it says not to use wirewound resistors here. However, all the sense resistors I see on Digikey seem to be wirewound. Am I missing something? Next, using the equation provided, R = 0.5 / I, 2.8A comes makes R= ~0.179. Since I know I won't be able to find this exact value, is it harmful to use a lower value, ergo providing more current? Or should I got the next step up and play it safe?

Thanks


- Jesse

[krazatchu]

You don't want an inductive resistor like the wire wound...
You might find some non-inductive types in a to-220 case with two legs instead of three...

Otherwise the sense resistor is just a normal resistor withing the power spec...

Michael

[Jesse B]

You don't want an inductive resistor like the wire wound...
You might find some non-inductive types in a to-220 case with two legs instead of three...

Otherwise the sense resistor is just a normal resistor withing the power spec...

Michael

Alright, thanks

[phomann]

Alright so I was just looking at the parts list on the PMinMO website, and I have a pair of quick questions about the sense resistors.

First off, it says not to use wirewound resistors here. However, all the sense resistors I see on Digikey seem to be wirewound. Am I missing something? Next, using the equation provided, R = 0.5 / I, 2.8A comes makes R= ~0.179. Since I know I won't be able to find this exact value, is it harmful to use a lower value, ergo providing more current? Or should I got the next step up and play it safe?

Thanks


- Jesse

http://search.digikey.com/scripts/Dk...nse%20resistor


Cheers,

Peter.

[Jesse B]

http://search.digikey.com/scripts/Dk...nse%20resistor


Cheers,

Peter.

Thank you very much, just found some metal-element resistors there; I swear they weren't there before

As for my other question (as these are only in .15 and .2 ohm), would more current hurt, or should I go with less?

[krazatchu]

The 0.15 ohm will give you a current limit of 3.3 amps...
The 0.2 ohm will give you a current limit of 2.5 amps...

As r= 0.5/I ... Then I= 0.5/r ...

I'd go with the 2.5 amp limit for starters...

Michael...

[Jesse B]

The 0.15 ohm will give you a current limit of 3.3 amps...
The 0.2 ohm will give you a current limit of 2.5 amps...

As r= 0.5/I ... Then I= 0.5/r ...

I'd go with the 2.5 amp limit for starters...

Michael...

Alright, thanks.

[Matilda]

The TB6560HQ looks like a simple solution, but the current isn't adjustable.
Has anyone used it? In comparison to the Allegro A3977.
Does it drive nice? Is it smooth?.... and Quiet?

I wouldn't compare it to the A3986 which is the focus of this thread.
The toshi is max'd at 3Amp designs isn't it?
The A3986 can push a lot more power with the external fets.

Becuase I need adjustable current, I would stick with the A3977.
I have a motor board I designed & laid out. Runs sweet. Adjustable current & PFD.
Opto isolation on the drive signals as well.

In fact, I did two boards. One has a codlfire processesor on it. MCF5213CAF66.
Which also has an ethernet module.

Now I'm in need of more power.
My A3986 board is "working"... but the audiable noise is killing me.

Cranking Vref (Current Limit) down doesn't do anything.
I've tried driving in the 4 decay modes, all while adjusting the OSC.
Nothgin really.

I'm sure the chip could be to blame, but I've spent so much time with this. Not quite ready to throw it out the window!
I must scope my fet drives.
Could be a timing issue there?

[Matilda]

:drowning:

[liwenz]

hello,thank you

[Elco01]

Hello everyone,
Just registered for these forums, looking for applications of the A3986. A pretty interesting discussion...

I have an electronics engineering background, but work (managing a software company) kept me from spending much time on related hobbies, but I will have more time in the future, I hope. My plan is to build a CNC machine for woodworking, and recently I bought a number of new Strogra SM56.3.18.J3 steppers (1.25 Nm, 1.5 Ohm, 3 mH, 4.2 A bipolar) on a sale. After a lot of Googling I found the A3986, but it does not look like the perfect solution? For power MOSFETs I have plenty of STP35NF10's.

Microstepping looked interesting more for a quiet operation than for accuracy. I can manufacture 2 player PCBs at home (Eagle license), but I'll be happy to buy an existing design. Any suggestions?