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DRV8711 nFault

liur
Prodigy 180 points
Other Parts Discussed in Thread: DRV8711

Hello,

The DRV8711 and CSD88537 are employed to drive a stepper motor in our project. However, after performing some test routine, we found that the DRV8711 chip is very unstable, the phenomenon can be summaried as following:
1. The register bit STATUS[5:0] fequently become 0x3f when the motor current increase to above 2A or change to high resolution microstepping (64~256);
2. The motor current occasionally become unstable in hold mode(no any communication between MCU and DRV8711), for example the original current is 1A, but randomly it changed to 3A or 4A then back to 1A;
The applied setting is below:
ABT = 0;
DECMOD = 1;
TBLANK = 150(3us);
TDECAY = 24(12us); 
TOFF = 48(24us);
TDRIVEN = 1(250ns);
TDRIVEP = 1(250ns);
IDRIVEN = 0(100mA);
IDRIVEP = 0(50mA);
We also tried all kind of setting combination by following up the guide of application note SLVA637/SLVA714/SLVA632, but the failure phenomenon cannot be eliminated.
Could you please enlighten us how to locate the root cause for this failure?
Thanks and Regards
Liu Rong
  • 0
    TI__Mastermind 26065 points
    Hi Rong,

    Since you have consider lots of about the register settings, I think the problem maybe because of the hardware.
    Could you give your full schematic? SPI frequency? Layout picture?

    Also please give your motor's DC resistor of the phase.

    Have you tried all-mixed decay mode with parameters in SLVA637? Also set TBLANK to smaller one about 1 to 1.5us.

    The DRV8711 is proved stable running in our lab and many customers. There must be some hardware/software issues in your design. Let's find it and get a good result.

    Best regards,
  • 0 in reply to Wilson Zuo
    Prodigy 180 points
    Hi Wilson,

    Thanks for your quickly response. Could you please send me your email box so that the schematic and layout can be attached? The SPI requency is 281khz(36Mhz/128), stepper motor's DC resistor: 1.1ohm, inductance: 2.2mH; We also tried varies parameter in all-mixed decay mode (DECMOD=5), but it seems no useful, the motor current become more unstable if we set TBLANK < 3us；we use 47ohm series gate resistor for low side mosfet and set DTIME to 850ns, I think maybe the current loop is unstable so I check the spike voltage on sense resistor, the ripple p-p voltage is about 90mV maximum for one phase, about 40mV for another phase, is necessary to add filter between sense resistor and xINSENx pin as described in Figure 12 of DRV8711 datasheet?
  • 0 in reply to liur
    TI__Mastermind 26065 points
    Hi Rong,

    For the filter of current sensor, so far, we acctually find there is no need to add any RC or C filters to the Rsense circuit. This is proved in many different layout practise. So if you have the filters, please have a simple try without it.

    Best regards,
  • 0 in reply to Wilson Zuo
    Prodigy 180 points

    Hi Wilson,

    Thanks for your professional suggestion. After removing the filter resistor and capacitor, the current unstable phenomenon has been almost eliminated,  but the STATUS error still happen occasionally.

    Best regards,

    Liu Rong