Hi there. Has anyone used an A3982 with an mbed board?

http://www.allegromicro.com/en/Products/Part_Numbers/3982/3982.pdf

I am having a little bit of trouble getting the thing to work. Every time I connect the Vcc to the regulated 3.3V of the mbed for the logic ref the IC gets starts to get very hot.

Also all the outputs are being driven i.e. they have a full 14V on each Out pin therefore the motor will not run

Here is schematic of my board

http://makeyourbot.wdfiles.com/local--files/a3982-1-0/sch.pdf

I have checked the connection repeatedly and even changed the IC I suspect that i am setting the Itrip values incorrectly. Currently I have Rs as 0R2 and Vref as 1.6V to give me a trip current of 1A. (Itrip = Vref/(8*Rs))

The only other factor i can think of is that the mbed output is 3.3V compared to the 5V that the circuit is designed for but still while it might explain the strange output voltages, I don't understand why this would make it hot.

Please does any one have any experience hear with this IC?

Hello this seems to be an old thread. Did you manage to solve the problem ? What was the issue? I'm having the same problem on a board I etched based on common design and I' ve found some threads with the same issue buto no response . TIA, Giancarlo

I have been running A4979 chips with an mbed nucleo without any problems. These are newer versions of your chip but otherwise similar. The allegro chip should only draw a few milliamps and according to the datasheet the A3982 should operate on 3.3v without a problem.

Have you put a meter on it to check the current draw?

It's important to keep all the power and ground lines sorted out of course. Is there a ground path between the motor supply and logic supply?

Is the mbed drawing power from the USB port? I would suggest running an external regulator from the motor supply to power both the mbed and allegro chips. I needed 5V as well and ended up with a 5v regulator that fed a 3.3v regulator for the allegro chips and also the 5Vin on the nucleo.

Hope this helps... Doug

Thx, Dug for you suggestions, sorry to be late but I hardly hoped to get a reply so I was a bit sloppy in checking for one. Actually I partly solved the problem : I got the drivers working simply putting an microprocessor to drive the step line instead of doing it by hand ( possibly I' m too slow). The problem I have at present is that the drivers worked fine as far as I powered them with batteries (5V logic, 9V power) but looks like I managed to fry them by powering with an adapted ATX supply (5V ,12V ) possibly the supply is not that stable, so I think I'll follow you in adding a voltage regulator . Thx again, Giancarlo

If you are only making a prototype, then I would recommend getting a step-stick, or similar for 3D printer,

like step-Stick

No brainer, the whole thing is cheaper than the chip from Farnell !!

Ceri

Giancarlo: The switching power supplies usually have a minimum load for some or all of the outputs. They won't regulate the voltage well otherwise and inductive loads like motor windings is only going to make things worse. Try putting a light bulb or even a high-power resistor to pull down the outputs and working from there.

Doug

I have a PC power supply 300W, using just 12 Volts,

with no problems on my PCB

Ceri

@Dug I already have a 10W resitstor internally connected to 5V, possibly I should add another to 12V. @Ceri Yes, I sure could just buy a driver ( Btw the price of that one is incrediby appealing ), but what about the fun of designing and testing one ?

Giancarlo