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DRV10987: In No Motor Fault state, FG signal has abnormal PWM signal

Annie Liu
Genius 10295 points
Part Number: DRV10987

Hi Team,

The customer is experiencing below issue and needs your help.

The FG signal of drv10987 is the real-time feedback motor speed signal of stable closed-loop state， When error is detected ,the FG signal will be pulled up to "High". But now a problem is found in the application, when the U\V\W are in poor contact or no contact(Before the no contact the motor works normally), FG outputs PWM signal and the frequency decreases gradually ( config detect no Motor Fault)， In this way, the system mistakenly assumes that the motor is still rotating. So how to set the config register to feedback the condition of no contact of U\V\W?
Now my EEPROM Config is follow:
0X90 0X102E
0X91 0X0B3A
0X92 0X08C0
0X93 0X12EB
0X94 0X3B0F
0X95 0XF843
0X96 0X006A

Thanks,

Annie

  • 0
    TI__Mastermind 24415 points

    Hi Annie,

    Thanks for posting your question in MD forum.

    The phase U current is checked after transitioning from open loop to closed loop. If the phase U current is not greater than 140 mA then the motor is not connected and this condition is treated and reported as a fault. FG signal is generated by detecting the zero-crossings of phase U current.

    1. Do you know which phase is not connected to the motor? If it is phase U then I expect FG to be pulled High as there will be no current in phase U. 

    2. Is the motor disconnected from the device before the motor enters closed loop or after closed loop? From your post, I understand that the device detects "No motor fault" so I'm assuming the motor is disconnected before the device enters closed loop. If the motor is disconnected after it enters closed loop, then the device will not detect "No motor fault" as this fault check is done after transitioning from open loop to closed loop.

    My suggestion will be to read the fault register (address: 0x00) bit 3 to know if there is a "No Motor Fault". If this bit is set to 1 then we can ignore the FG signal as the motor is not connected to the device. 

    Regards,

    Vishnu.

  • 0 in reply to Vishnu Balaraj
    TI__Genius 10295 points

    Hi Vishnu,

    Thanks for your reply.

    Yes ，the motor is disconnected after it enters closed loop. Now ,When the motor doesn't rotate, my system needs hardware protection (There is a delay in the software reading register), so I use the FG signal to detect the fault of the motor(Hardware detect).

    Configure EEPROM to detect wrong KT,when motor is disconnected on closed loop,FG will pulled up to high .But Kt will change with the speed 、temperature read by the DEV10987 Demo Tools. I'm afraid there will be mistakes when motor works well. So any other reliable hardware detect suggestions?

    Annie

  • 0 in reply to Annie Liu
    TI__Mastermind 24415 points

    Hi Annie,

    I'll respond to your question shortly!

    Regards,

    Vishnu

  • 0 in reply to Annie Liu
    TI__Mastermind 24415 points

    Hi Annie,

    I agree that there will be a propagation delay in the order of microseconds in reading the registers. Is your system not tolerant to this delay? Adding external current sense resistors in series to either the power supply or the phases will be the next option but I see this as a complicated process in terms of implementation. The best way to detect no-motor fault without making any hardware modifications will be to read the fault register or measure the change in frequency of FG signal as suggested in my previous post.

    Regards,

    Vishnu.