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DRV8256PEVM: Unable to change Itrip and other failures

Mark81
Expert 2610 points
Part Number: DRV8256PEVM

I bought a DRV8256PEVM to test the driver before select it for my new board.

First some incongruences:

  • on the product page I read "Up to 1-A peak current", in the manual I read "The components can support peak output currents up to a maximum 4A" while on the silkscreen I read "Board rated for 2.5-A peak for half-bridge". Which is the correct one?
  • in the schematic the P version (PWM) requires an high level for the INTERFACE signal, hence R6 should be populated (pull-up). Instead on my board R5 is mounted instead. Why?
  • in the schematic there are two voltage settings: 24V or 36V (and set 36V via R2), while on the silkscreen, in the manual and in the product page the maximum voltage is 48V. Again, which is the correct one?

Now I describe the issues using the board. By the way, I need to re-install the software every time I launch it (I'm using Windows 10). When the installation finishes I click "open" and it runs the software. If I close it, I cannot open it again, even restarting the computer. It closes the process in a while without any output (even from console). I need to re-install and open from the installer.

First issue: the right pane shows AIFS 0.5A no matter the position of the current slider. I guess this should reflect the current Itrip settings. What does AIFS actually mean?

Second issue: moving the current slider does not change the Vref on the board. While the other settings lead to a change in voltage (i.e. 0V, 3.3V, etc...) there is no DAC output. Better, both are stick a 970 mV.

Third issue: I removed R27 and R28 to provide an external Vref. Even with both Vref at 3.3V I get a fault condition when the average current consumption is above 1 A.

Fourth issue: the chip becomes VERY hot even at small currents, like 600 mA.

I'm using a DC brushed motor @ 24V. Powering the motor with a constant DC voltage it draws 350 mA. I'm not able to run it with this evaluation board. I tried all settings but I get a fault condition before the motor moves a bit. Only with a fast decay and 32 μs Toff it can barely spin. The current consumption (on my power supply) rises above 1 A at very low speed (IN1 ~ 15%) and I suddenly get a fault condition, with Vref = 3.3V!

Please, would you help me to understand if I'm missing something? The driver should be capable to control motors up to 5A but right now it seems I wasted time and money...

  • 0
    TI__Mastermind 37683 points

    Hi Mark,

    Let me start by answering the three bullet point questions:

    • Please disregard the 1-A rating stated on the EVM tool page description. It is not correct, I will work on fixing that. The 4-A max peak output current rating is how much current the DRV8256P IC can per half-bridge before an Over-current fault (OCP) is triggered. So to prevent the driver from going into OCP, ensure that the total max peak output current is below 8-A (2 x halfbridges). The 2.5A is the max continuous current that the board can handle before the temperature increases above 130C (max temperature rating of the PCB material). I hope this clarifies your question.
    • This EVM design files have many variants. The correct design variant for the DRV8256PEVM is MD027A(013)_Sch.pdf. So if you open up that document, R6 is populated. Can you send me a picture of the top and bottom of your board to confirm?
    • This EVM was designed to support various devices. Some of these devices have higher voltage ratings that others. In the case of the DRV8256PEVM, the max recommended input voltage is 48-V.

    Now regarding the GUI issues,

    • I don't see the GUI issues from my end. I even re-installed the GUI but I am able to re-open the GUI after closing it. If you have a computer from your company, check with your company's IT if the software is being blocked. If you have a personal computer, i recommend trying to install the GUI there.
    • It looks like you have selected the wrong EVM GUI variant. The AIFS is only present for the 84xx devices. Try to select the DRV8256P variant and try again.
    • I think most of the problems you listed are a result of choosing the wrong GUI variant. Choose the DRV8256P variant and try to drive the motor again. The DRV84xx are stepper motor devices so the control scheme is different than the DRV8256P which is a brush DC motor driver. Please try again and let me know if you have the same issues.