DRV8873: Open load detection on DRV8873

Hey Maurtis,

Did you write a 1 to the EN_OLP bit?  For the SPI version of the device the open load test is run on command, not constantly. 

See 7.3.2.4.1 Open-Load Detection in Passive Mode (OLP) - snipped below, but it continues for a couple pages and has a good diagram about it:

Also it looks like Open Load bit is an information-only diagnostic, meaning it doesn't disable the outputs when open load is detected.  I think this helps explain why you can still control your motor even after open load condition is detected and reported. 

Best,

Jacob

Thank you for your message. We will test this feature soon. Maybe another approach, which brushed DC driver would you suggest with the following requirements?:

- In our application, the driver is actuating a linear motor (24V/3A). 

- The motor driver is on a rail vehicle (moving) and the linear motor is on the end of the rail.

- We want to constantly use the OLD function while the vehicle is moving and (at the end of the rail) to detect and power the motor if a slide contact meets the vehicle.

- While on this slide contact, the linear motor is actuated until it reaches its own end switch (fully extended). At this point the forward current is blocked and a parallel placed 10k "dummy" resistor can only be seen from the driver perspective. 

In conclusion; the driver needs to be able to do a (semi) continuous OLD to check for the actuator. It also needs to be able to see the 10k resistor as a load (so no OLD triggered). 

We can use either SW of HW operated drivers.

Thank you

Hey Maurits, 

Correct me if I'm wrong, but would this application be better suited with Current Sensing or Stall Detection instead of Open Load Detection? Current sensing so that you could detect when it reaches the end by a spike in current.

Also can you post a picture of it just to help me visualize it?  Is this on a model train set? 

Given what you describe I think you might be able to get open load detection working with some trial and error, though it isn't exactly how the feature is designed to be used.  I wonder if you would be better served just using a small cheap microcontroller to sense the 10K resistor or slide contact and use that microcontroller to send a signal for it.  

The DRV8243 is a much newer device with open-load detection and integrated current sensing at a similar price to DRV8873, you should check it out and see if the newer OLD control will work better for you: https://www.ti.com/product/DRV8243-Q1 

Best,

Jacob

Hi,

The application involves a stairlift on an aluminum profile/rail. To save space in small houses, the ~1m end of the rail can be folded/pivoted upwards. The linear motor is controlling this motion. Because the motor driver is located on the stairlift, it can not sense/power the motor when not at the end slide contact. Due to safety concerns we want to first sense the motor at the slider contact, and then perform the upwards folding of the rail. 

You say the open load detection is designed with a specific way of application. What is the idea behind this function?

We ordered the DRV8243S-Q1LEVM to check the OLD and OLA functions.

Thank you

Hey Maurtis, 

Ahh okay understood, thank you for the detailed explanation! 

First can you compare your circuit to this circuit in Open Load Detection in Integrated Drivers:

That application note has a lot of good info about getting OLD working

Maurits Oldenhof said:

You say the open load detection is designed with a specific way of application. What is the idea behind this function?

Apologies, the 10K resistor was throwing me off.  What's the capacitance of your load?  Wondering if from the below paragraph you need to tweak the OL_DLY 

Best,

Jacob