# What is meant by current sense?

Discussion in 'Embedded Systems and Microcontrollers' started by allahjane, Feb 20, 2013.

1. ### allahjane Thread Starter Member

Sep 19, 2012
75
1
Hey there,

I'm Using L298N motor driver for my application. It has certain pins labeled in datasheet as "current sense A" and "current sense B". What are those for? I read somewhere that you need to connect them to ground if you don't use their function.

That's one thing, but what actually is the function of those pins and how can I use that functionality?

I'm getting a feeling that it has something to do with limiting the current flow through it

2. ### MrChips Moderator

Oct 2, 2009
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5,294
Motor drivers need to measure the current used by the motor in order to shut down the motor when the motor stalls. Current sense A and B are connected to a resistor that is placed in series with the motor.

3. ### allahjane Thread Starter Member

Sep 19, 2012
75
1
Can you please explain in more detail? can I use different resistor value to trick the driver to think that the motor has stalled, when my desired current is reached?

4. ### MrChips Moderator

Oct 2, 2009
17,119
5,294
Sorry, I just read the data sheet for the L298.
This is a dual full bridge driver. Current sense A and B are for the dual drivers, one for each motor winding. All the info is in the data sheet.

May 11, 2009
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6. ### ErnieM AAC Fanatic!

Apr 24, 2011
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What are those for/what actually is the function of those pins?
At the bottom of the data sheet (linked above) page 1 is the BLOCK DIAGRAM. The current sense pins 1 & 15 are simple the pins at the lower end of the H bridge where all the return current from each bridge goes to ground. By inserting a small resistor there one can measure the current thru each motor. If measurement is not needed you have to short the pins to ground to allow current to flow to ground.

something to do with limiting the current flow?
Not directly in any sense. A small resistor is typically used there least real power be lost in the resistor. A better less wasteful approach would be to monitor the voltage on the resistor (and hence the current) and turn the drive signals off if an overage is noticed. A comparator may be used for this sense.

7. ### allahjane Thread Starter Member

Sep 19, 2012
75
1
The datasheet won't give enough explanation that's why I'm asking it here

8. ### allahjane Thread Starter Member

Sep 19, 2012
75
1
but that means if the load is leeching more than safe current then the motors will always be off.

is there nothing one can do to limit the current (not stop it) without resistors

9. ### allahjane Thread Starter Member

Sep 19, 2012
75
1
Well what actually will happen if the current supply capacity of the source is significantly less than that allowed by the limiting resistor?

Will the limiting resistor decrease the current even further?