09-14-2008, 01:31 PM
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| | | Join Date: Jul 2008 Location: United States of America
Posts: 22
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 SLA7024 Unipolar Stepper Driver Chip! | |
Guys,
First of all DON'T WASTE YOUR TIME trying to get the SLA7024M INSTEAD go for it's bigger brother the SLA7026M, WHY well the 2 reasons that I see are as follows. The 7024M is rated for 46VDC MAX @ 1.5A'S while the 7026M is rated for 46VDC MAX @ 3A'S. The second reason is the fact that it is a pin for pin drop in replacement part, hence the internal fet's are rated for double the current. Now it does also have a 5A Max spec but at 3A's you are in the parts safe range, but bold on a better heatsink, get some airflow across it & you could probably get another 1-1.5A's out of it w/o damaging the part but as most motor windings 3A'S is plenty you probably would never have to do that,
So you should be able to buy the parts thru allegro or maybe on ebay and the 7026M would drop in place & operate as needed. But again check the datasheet as they may ask for a different current sense resistor but for sure they would require a higher powered one but again that is easy. As you are now using a part that has double the current you need a current sense resistor that has double the original power rating. So if it calls out for a .68 ohm resistor at 2W you can put 2 1.36 ohm 2w resistors in parallel or just go find a .68 ohm resistor at double the current rating. Depending on area to work with a good one to use is a 30W TO-220 packaged part which is thin & you can bend the leads to fit into the original holes then add on a small heat sink to heat remove the heat. They go for about $3.25 at mouser electronics & are made by caddock & other mnf's. But always try to get & use resistors that are low inductance, wire wound is one large inductor.
Now here are some bad points. 1st of all there are only the 2 phase inputs thus no enable or inhibit lines. In most designs there is an inhibit line for each phase But that can be added by placeing AND gates in fron of each of the 4 lines & using 1 common input for each pair as the inhibit or enable line, thus w/o a high on each of the 2 enable lines nothing gets to the driver. But again not all designs use this but if you used lets say a ST current pwm controller like part number L6506 it has the needed AND gates built right in & would be an easy hookup to your board that you want to build. Plus it adds in current controlled pwm'ing thus you now have a really nice circuit except that you still need a controller so if your not planning on writing your own code for a PIC or Atmel microstepping controller & Full & Half steps are O.K for you then forget the L6506N & go straight to the L297N which has the L6505N built in plus everything else needed to allow you to operate the board you want to build from 3 inputs, step, direction, & enable. So when & if you do go with this board keep in mind what you want to control it with. If you do not need or want microstepping ae full, 1/2, 1/4, 1/8, 1/16 steps then use the L297N or replacement but if you DO WANT MICROSTEPPING the use the L6506N in front of your board but after your PIC or ATMEL mpu that you programed to do the microstepping. If your a good enough programmer you can get rid of the L6506N as you can do all of it's functions using your mpu chip as long as it has 2ea ADC converters. Anyway good luck, & be safe.
baggs  |
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