24VDC motor overcurrent monitor

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alexxx

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I would like to use an overcurrent monitor for a 24V DC motor application. The motor current varies, from 2A to 5A max. After some web digging, I came up to this dedicated IC.

**broken link removed**

It is convenient, SOT23 package, with only 2 external components and in a fair price. My main concern here is the load. Will this IC operate OK with the motor as load? I'm worried about the high transients from the motor. Is this going to work, or should I stick to more traditional methods like instrumentation amplifiers?
 

I haven't used this exact device, but used a very similar one from Linear Tech.

My experience is that the component one must be concerned about during overcurrent transients is mostly the sense resistor.
Since power dissipation increases with the square of the current, a stall current of 3 times the run current will result in 9 times the resistor dissipation. If this condition is not rapidly removed, the resitor will degrade or burn out.

Even with a fast motor disable, I would advise a substantial resistor power up-rating, I would say at least twice the normal running power.
 
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    alexxx

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Luckily the sense resistor is well tested, in a similar application with a differential amplifier as feedback.
So schmitt trigger, since it is the first time I'm looking into dedicated ICs in current sensing, and reading the datasheet, I came to the conclusion that the load current could be as high as I want. I will have to use low Rsence, in order to avoid large Vsence values. Did I get that right?
Finally, my concern is Vsence, I am afraid that spikes will constantly drive Vsence to higher values that the absolute ratings. Did you use the similar IC in a motor load application?
 

You have a point about brush noise. Its peak value can exceed the maximum allowed by the IC. Whether this will destroy the IC or just cause malfunction, depends on the actual noise level.

But it makes sense to reduce the noise, brush noise affects more than only the current sensor, it could also wreak havoc on microcontrollers.

The first would be to filter the noise right at the motor terminals.
And the second, is to add a small RC filter in series with the IC's sense terminal.
 
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