L298 question

[WillHuang]

Hi all,

On the L298 bridge driver, there are 2 pins for current sense. In the designs that I've seen, most people use a sense resistor between these pins and ground the determine the current. With this, I have a couple of questions:
 
1) am I right to say that the calculated current from Vsense/Rsense is the current through a motor?
2) Can i replace the sense resistor with a hall effect sensor and still get the same effect? (e.g. ACS712 https://www.sparkfun.com/products/8882)
3) If I wanted to parallel the output a heavier load, would I need to connect the two sense pins together in order to measure the total current?

[wraper]

1) yes
2) depends on application, you should be concerned about bandwidth too. If using Hall effect sensor, it is not necessarily to connect it there. It can be connected in series with the motor as they have insulated output.
3) Current through the drivers won't be shared equally. Don't connect them in parallel.

Suggestion, throw L298 in a garbage bin of history, it sucks. Get some newer IC.

BTW what do you intend to drive with it? Current sensing is essential if for stepper motors. Not so much for brushed DC motors.

[WillHuang]

We are planning to drive DC motors and would like to measure current just to collect some data.

What motor drivers would you recommend?

[wraper]

motor spec? Voltage, max working current, max inrush current?
Also it may be better to use MOSFET bridge driver IC + discreet mosfets (more resistant against overload events).

[WillHuang]

Well the idea was to build a system that would determine the characteristics of an unidentified motor. We were hoping we can measure voltages, current, and rotational speed to determine these characteristics

[wraper]

Then I don't suggest bridge integrated in the IC. Most likely you will blow up them sooner or later when testing unknown motors.

[Ammar]

3) Current through the drivers won't be shared equally. Don't connect them in parallel.

The data sheet says you can in fact do this. Provided you parallel channel 1 with 4 and 2 with 3.

http://www.st.com/content/ccc/resource/technical/document/datasheet/82/cc/3f/39/0a/29/4d/f0/CD00000240.pdf/files/CD00000240.pdf/jcr:content/translations/en.CD00000240.pdf

This won't double the current carrying capacity, it says it can take it from 2 to 3 Amps. Whether you can put drivers in parallel depends on the topology and technology.

In this case, the drivers are on the same die, so thermal matching is reasonably good. However, you are right in taking precaution, as connecting two different devices on different die would result in the current not being shared equally. For example, stacking two L293 ICs on top of each other only increased the total current carrying capacity from 1A to 1.2A.