Defeating the enable pins on an L298N dual full bridge driver

Oct 11, 2003 2 Replies
M

I want to drive a bipolar stepper motor through an L298N, with the logic coming directly from a PIC. My prototype works fine, however, I need to use 6 ports for the motor (2 for ENA/ENB, and 4 for IN1/IN2/IN3/IN4).



I want to elimate the need to dirve the enable pins, therefore requiring only 4 ports to drive the motor. I have come up with a couple of ideas, and would like other peoples opinions as well.


1) Tie the ENA/ENB directly to Vss via a 10K resistor
2) Tie the ENA/ENB to IN1/IN2 and IN3/IN4 (respectively) through diodes
3) Use TTL OR gates, with inputs from IN1/IN2 and IN3/IN4 and outputs to ENA/ENB(repectively).

I suspect the best alternative to be #3, but...



Thanks - Marty


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G

There is yet another option: drive it though the L297, which is made to interface with the L298. The L297 is a stepper translator, and needs at a minimum Step and Direction inputs to control a bopolar stepper. It will produce standard, wave, and half stepping. With a handfull of passives you can build a quite nice chopper drive, which is very desirable for a bipolar stepper. There are ready-made "pro/am" PCBs available, if you want to go that route (one is at

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ST's app note shows some simple circuit examples.

Depending on the source, the L297 costs about $6-7 in low quantities. This is a little more expensive than a couple of gates, but IMO it's the better approach for bipolars than using the L298 just by itself.

-- Gordon Author: Constructing Robot Bases (Forthcoming) Robot Builder's Sourcebook, Robot Builder's Bonanza

Marty wrote:

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R

Hi Marty

Use the enables as part of the switcher circuit that limits the current in the windings. If you don't want to do that, just hard wire them enabled.

The 297 is a pain because you have to switch the half/full step pin at the right moment to make it work and you end up losing more processor pins than you save. I couldn't figure out how to hard wire it so I designed it out.

best regards

Robin G Hewitt

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