• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 30 subscribers
  • Views 1708 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DRV8825 connected properly but no response from motor output pins.

Dmitry Ponomarev
Prodigy 140 points
Other Parts Discussed in Thread: DRV8825EVM, DRV8825

Good Evening,

I've designed a prototype board to the DRV8825EVM schematic. (http://www.ti.com/tool/drv8825evm)

The motor driven is a bipolar stepper

The ISENSEA/B resistors are 2W            0.4ohm each

The MCU controlling voltage is 3.3 volts

MODE0 and MODE1 are tied to 3.3V, MODE2 is tied to GND, this gives me 8 microsteps/step

A/BVREF is set to 1.6 volts (tried setting to 3.3 volts as well)

VMA VMB are driven by 15 volts

nSLEEP, nRESET are both set to 3.3 volts

CP1 and CP2 are connected to 0.01uF cap       VCP is connected to VMA and VMB by 0.1uF cap 

V3P3OUT is connected to ground by 0.47uF cap

STEP is driven by a 500Hz, 3.3Volts square wave (also tested 50Hz without success)

DECAY is open (mixed)

nENBL is set low by the MCU

DIR is set low by the MCU

nHOME and NC are not connected,

nFAULT is connected through a pull-up resistor to 3.3 V

Here is the issue: 

When the MCU is powered on, the signals are sent to the motor, but I don't see any output on the A or B OUT 1 and 2, with or without the motor connected, the outputs just floats around 3 volts constantly.

Originally, nSLEEP and nRESET were powered by V3P3OUT, however I noticed that the regulator doesn't turn on unless the nSLEEP is driven high, and therefore I had to connect all 3 of these to my 3.3V regulator output for the MCU.

nFAULT stays high the whole time, meaning the DRV8825 shows no issues

I tested this on 2 DRV8825 chips and 2 PCBs without any success

Does anyone know if I May be missing anything? The only difference with the EVM board, is that it allows the user to control signals to nSLEEP and nRESET and mine just ties them to 3.3 volts. Is there a problem with enabling these two simultaneously that may be causing this?

Is the RSENSE of 0.4 Ohms too high?

Thanks,

-Dmitry

  • 0
    TI__Expert 8885 points

    Dmitry,

    The electrical interface and logic levels for Enable, Reset and Sleep mentioned by you are all fine.

    It appears to me that it is related some assembly issue in your board/PCB. Many occasions I have noticed that if Power-PAD beneath the IC is not solder to GND plane of PCB properly, functionality is affected. Please check this out. You can also measure the V3P3OUT from IC, if it is coming than IC should function properly.

    Best Regards

    Milan

  • 0 in reply to Milan Rajne
    Prodigy 140 points

    Good Morning, thank you for the prompt reply. 

    The power pads are connected to the ground layer, I noticed that on the chip, they are not grounded internally. This made no difference and the chips still output a constant voltage on A and B OUT 1 and 2 pins. 

    I also tested V3P3OUT and it output 3.3votls

    Is there a minimum and a maximum frequency that these chips will accept ont he STEP input?

  • 0 in reply to Dmitry Ponomarev
    TI__Mastermind 26065 points

    Hi Dmitry

    It is weird. Sounds all things are correct. How about your VM cap? is it big enough (>100uF) and close enough to the VMA and VMB PIN?

    Also you can check whethe VCP is around VM+(~10 to 12V)?

    STEP has no MIN and MAX is 250k.

    And other maybe excess check is about the motor connection.

    Thanks.

    Wilson 

    Motor Application Team