DRV8825EVM: DRV8825EVM Fault Pin Issue

If set Current is low requirement of Motor Current to run or if any disturbance or Motor stop due to any mechanical obstacle, then Fault pin should gets low as per datasheet, But it is not working ??? Please suggest how to fix this problem ???  

Hi Jitender,

JITENDER KUMAR said:

If set Current is low requirement of Motor Current to run or if any disturbance or Motor stop due to any mechanical obstacle, then Fault pin should gets low as per datasheet, But it is not working ??? Please suggest how to fix this problem ???  

Did you measure the motor current during the motor stall? This device does not have any type of motor stall detection. Instead, an OCP (over-current) protection is triggered if the motor current goes above 3A for longer than 3µs. If your motor current is below 3A, that would explain why OCP fault was not detected by the driver.

Regards,

Pablo Armet

Motor Drives Applications Team

Ok If Motor current goes above 3 A only then Fault pin gets low, otherwise not???

My Motor maximum current of 0.7 A, SO I set reference accordingly, But if current exceed 0.7 A, even after that fault pin not getting low ?

As per my circuit I set 1.25 A current limit, If Motor current exceed 1.25 A, then fault pin should pull down or not ? May you please explain

?

Hello Pablo, 

Thanks for describing the difference, It means that:

1. OCP limit is fix 3 A in DRV8825

2. Current regulation limit can be vary. if any Motor has maximum current limit 1 A, then Current can be regulate max 1 A, but there are no indication  or signal fault state from DRV8825, if Current exceed above 1A.

To sense this condition, there need of any external current sensing circuitry to interface with DRV8825 ?

May you suggest how I can sense this condition if my motor current exceed 1A current and I want to sense it for Motor Protection. please

Thanks & Regards

Jitender K. Dhiman

Thanks Mr. Pablo,

For your valuable suggestion/answer of my doubt.

I will read this voltage at ADC of MCU & will update you.

Thanks again.

Regards

Jitender Kumar

Hello Mr. pablo,

I studied your FAQ article & try to sense voltage at Pin no. 6 & pin number 9 of DRV8825 at which 200 E resistance is used, but voltage not showing May you please check my circuit I share with you. ans suggest  me

Jitendar,

How much current is your load consuming? The schematic looks good to me. Maybe the current is very low and is not generating a noticeable voltage drop across the ISEN resistor.

Regards,

Pablo Armet

I am using Motor having below detail:

I am using Motor in free condition just for testing & stall it manually to check Voltage at ISEN, But it is not showing voltage in running condition & in Stall condition,  Motor Rated Current is 0.7 A.

Please suggest.

Hi Jitender,

With 0.7A and 0.2Ω, the voltage across the sense resistor will be around 140mV. Decrease the time scale of your oscilloscope and you might be able to see the samll voltage change. Are you actually measure a voltage change or is it 0V?

Regards,

Pablo Armet

Ok Let me check & will update you

Hello Mr. Pablo , I have checked Voltage accors 200 mE resistance , it is showing 0V. just showing noisy waveform during running of motor. Waveform attached for your reference. Also this noise does not vary in case of Manual stall of Motor Shaft. Please check & suggest

Hi Jitender,

Not sure what is happening in the waveform. Looks like maybe some noise is getting coupled to the ISENS pin.

Can you try looking at the supply voltage and output voltages as well. I'm curious if the noise is also showing up in other places aside from ISENS pins.

Another recommendation is to use a voltage probe with very small GND cable. Some probes come with spring hooks that can be attached to the GND connection. Place the GND spring tip on one end of the resistors and the actual probe on the other terminal of the resistor.

Regards,

Pablo Armet

Yes I have checked, but no voltage signal observed at this ISENS pin of both A as well as B coil. SO it is condition for me how to sense stall condition of Steeper Motor shaft.

May you suggest any other alternate solution to sense stall current of Stepper Motor if possible.

I am using 200 mE resistance in 0805 package, It may be reason?

What is the power rating of the resistor? is it enough for 0.7A?

1/8W

IC & resistance detail : R122 & R113 ARE OF 200mE

We have prepared own board for prototype testing . Everything is working ok, only this is this issue to sense stall condition of motor. Please check above detail & suggest

Hello Mr. Pablo.  After conclusion, You have cleared that

1. With DRV8825, Current sensing of Stepper motor  with resistance not possible.  So need some external circuit. So You will guide us some external circuit interfacing with that for current sensing.

2. Also suggested DRV8434A ic having stall detection feature, but this IC is out of stock as texas site, then how I can consider this IC for new design, please clear .

Thanks & Regards

Jitender Kumar

Hi Jitender,

Unfortunately the DRV8434A is out of stock at the moment. I can check with our team internally to find out when will have these units available.

Approximately how many units will you require and by when?

Regards,

Pablo armet