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DRV8262: DRV8262 Current regulation not working

Jake Lei
Prodigy 150 points
Part Number: DRV8262


Tool/software:

Hi, 

I am testing a DRV8262EVM module with following setup, but I see that current regulation is not working at all. Could you please support as to why It's not working? Below are my setup and scope images, 

  • Single H-bridge used in Dual mode configuration with PWM type Input (only 1 H-bridge, OUT1 and OUT2 used) 
  • Supply voltage 28V 
  • load current ~1.9A 
  • Decay mode : smart tune (tried to use slow decay which is not available in GUI. i.e., shorting pin to the ground, but didn't make much difference); this also did not make much difference 
  • TOFF : 16 us
  • OCPM : latch 
  • VREFEF : 2V (equivalent to current regulation level of 2.85A) updated from TI Cloud GUI. Also have measured through the scope and I didn't notice any distortion in reference voltage
  • Issue seems to appear both directions

Yellow = nFault 

Green = supply current 

I am seeing inrush current about 5A then settle to load current. I do not see nFault being triggered low. 

Zoomed out image

Red = IPROPI voltage 

So I don't know why there is such a long delay in IPROPI voltage and also why it does not trigger current regulation. It's already seeing a current higher (over 4A) than it should be regulating (2.85A) 

I expect the current waveform to be well regulated as per calculation. This shows me that not only current is ramping slowly but also not regulating at all..

Would you please provide support on this?

Thanks 

  • 0
    TI__Mastermind 46465 points

    Hi Jake,

    Thanks for your post. We may have had recent past conversations regarding this subject E2E post.  

    Jake Lei said:

    Below are my setup and scope images, 

    • Single H-bridge used in Dual mode configuration with PWM type Input (only 1 H-bridge, OUT1 and OUT2 used) 
    • Supply voltage 28V 
    • load current ~1.9A 
    • Decay mode : smart tune 
    • TOFF : 16 us
    • OCPM : latch 
    • VREFEF : 2V (equivalent to current regulation level of 2.85A) updated from TI Cloud GUI 
    • Issue seems to appear both directions 

    The DRV8262EVM uses 3.3 kΩ for RIPROPI1 and 2. Based on this if VREF = 2 V the current regulation would happen at 2.85 A. I'm reproducing the oscilloscope capture shared in the past E2E post with you. See below. For this capture VREF = 2 V yellow trace. Motor current blue trace inrush is regulated at the expected 2.86 A. Orange trace is the OUTx showing voltage chopping during current regulation.  

    Was the test load a brushed DC motor? We've noticed with certain motors the on-board MCU ADC may cause current regulation loop stability issues. To avoid such external disturbances it would be helpful to isolate the IPROPIx connections from the ADC input. This can be done by removing the below two jumper shorts, one for each H-Bridge. 

    We're currently updating the EVM User's Guide to include this information about isolating the ADC connections on IPROPIx. I hope this resolves the issues you were observing. Thank you.

    Regards, Murugavel 

  • 0 in reply to Murugavel4637
    Prodigy 150 points

    Hello again, 

    Thanks for your quick response. 

    I went back to lab and measured again with your suggestion. Below is the result. I am not sure why I am seeing so much noise imposed on IPROPI voltage. I think this is what's causing the inaccuracy of current regulation level. I am reading peak current of 2.5A(Green) where I am expecting this to be 2.85A with reference voltage of 2V. This is more than 10% error. Do you know what is causing the noise? Yes, I am using DC brushed motor. Result seems to be better without those jumper connections to ADC. But I am still curious how I can improve these measurements. I could technically tweak a reference voltage slightly to get desired current level for now. 

    Also, If I remove those jumpers that are connected to ADC input, doesn't that affect other performances of IC in EVM? I guess current regulation will work fine without it but I just wanted to make sure that I am not disabling other features by removing these jumpers. 

    Green = motor current 

    Red = IPROPI voltage 

    Zoomed in 

  • +1 in reply to Jake Lei
    TI__Mastermind 46465 points

    Hi Jake,

    Looks like the current regulation is working now. Not sure what's causing this noise. Is your EVM isolated with USB isolator? Perhaps you may want to try with different grounding of the scope probed. We've never seen this much error with all our bench tests including temperature ranges and voltage ranges up to 60 V. 

    Jake Lei said:
    Also, If I remove those jumpers that are connected to ADC input, doesn't that affect other performances of IC in EVM? I guess current regulation will work fine without it but I just wanted to make sure that I am not disabling other features by removing these jumpers. 

    The ADC inputs are only for the current readings display in the GUI which is a moving average calculation. No other impact to the driver. Thank you.

    Regards, Murugavel