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DRV8825 design and soldering

Radovan Petrovic
Prodigy 30 points
Other Parts Discussed in Thread: DRV8825, DRV8818

Dear,

I need to finish project with DRV8825, and need your assistance to be sure

1. Can you help me with sollution for soldering thermal pad of DRV8825. I made 0.3mm vias on top layer as suggested in datasheet. I tried it on prototype board without soldering thermal pad and there were no temperature problems, it was and will running on 100 - 400mA (motor is 400mA max). Now i need to be sure about it, but it is very hard to solder  thermal pad, even with a hot air, properly. Can i make some bigger vias and apply solder from bottom side or how ?

2. I saw some application on your website with 100nF capacitors parallel to Rsense resistors. Is it necessary ?

3. I put tantal capacitor of 47uF in parallel with 100nF on AVref, because of greater path, from V3P3OUT, i think it is OK ?

4. I reached inaudible motor frequencies ~30kHz , but with very lower current. Can it be accomplished in a different way ?

5. In current calculations i choose 0.5VDC for Voltage on Rsense and then calculate Rsense, knowing that range is -0.3 to 0.8 VDC. i think it is corect, otherwise choosing Vs 0.8V gives Vref=4VDC for 0.38A

6. Interafce to MCU is without serial resistors. Application note has 220ohm resistors on every line, can it be avoided, or it is important for DRV8825

Thank You

  • 0
    TI__Guru 55615 points

    Radovan,

    1)  Please take a look at the application note below:

    http://www.ti.com/lit/an/slma002g/slma002g.pdf

    2)  Not necessary, but recommended to avoid false trips on the internal current sense comparator.

    3)  It is OK if you feel it is needed. 

    4)  Please clarify this statement as I am not sure what you mean by a "different way".

    5)  I suggest just using the equation in the datasheet and calculating Rsense based on desired Ichop and sounds like you already have VREF = V3P3OUT, so plug in 3.3V for Vref.  Calculate Rsense and ensure it is <0.8V given as abs. max.  I think you are on the right path...just coming at it from a different direction, but you understand the variables.

    6)  We have these on our EVM so you can pull them out and solder in signals from an exteranl MCU if you prefer.  Not necessary.

     

  • 0 in reply to Ryan Kehr
    Prodigy 30 points

    Ok, Thank You

    4) DRV8825 is replacement for IC L297,L298. L298 do not have microstep, decay settings, and smooth operation. Output signal is 2.4KHz, in audible range, with DRV8825 there is less noise. I reached 30Khz output frequency, and motor work is noise free, but it is with less torque. I want to use higher torque and normal current settings 100-400mA and be in inaudible frequency if possible ?

    Current settings are: 500Hz clock, slow decay, 1/16 microstep

  • 0 in reply to Radovan Petrovic
    TI__Guru 55615 points

    Radovan,

    The DRV8825 is a fixed frequency device and the only knobs to turn are the current threshold and decay settings.  You could also descrease the micro-stepping rate which would give you more incremental torque per step.  Other than that, your hands are somewhat tied with this device. 

    You might take a look at the DRV8818 that gives you the flexibility to select off time and also adjust blanking time in the chopping circuit.  Through external RC components you can also select an adjustable slow vs. fast decay ratio during the decay periods.  Micro-stepping is limited to 1/8 on this device.