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INA240: output of the pwm rejection amp (ina240a1pwr) has oscillation, how can i remove or prevent it?

Jaesung Oh
Prodigy 40 points
Part Number: INA240

Hi, I'm Jaesung Oh at Rainbow Robotics. 

 

We are a robotics company making cobots in South Korea.

We use ina240a1pwr for sensing the motor phase current, and normally we use it well.

 

but in some cases, we can find a situation the output of the sensor(ina240a1pwr) has a big noise.

usually, it happen after motor's big acceleration or deceleration.

after it occur, there is no way to recover this situation without cutoff the power. 

when we turn on the power again, the output signal of the ina240 is returned. 

can we get some information or method to prevent this event or situation?

we just want to know the reason of this, and we want to try to avoid this situation when we control the robots because it make the noise and unstable motions.

please let me know the answer.

 the output signals is captured, and i attach it on this post.

the signals can be captured by using MCU ADC, and also it can be shown in oscilloscope. 

  • 0
    Guru 140200 points

    Hi Jaesung,

    the INA240 may become instable due to a too high capacitive load. Can you show a schematic?

    Kai

  • 0
    TI__Mastermind 34240 points

    Hi Jaesung,

    Aside from a schematic, what additional information can you provide? The following would be good to know:

    In the scope photo, is CH1 the output of a bad part and CH2 of a good one's? Does the problem occur on all phases? Can it be reproduced on all parts?

    Regards, Guang 

  • 0 in reply to Guang Zhou
    Prodigy 40 points

    we use this product to measrue the bldc motor's phase current. as your saying, ch1 is the signal bad part's, and ch2 is for good one's. This situation can be created repeatedly, and the amp producing the loudest noise is random. Sometimes there are cases where even large decelerations have no effect.

  • 0 in reply to kai klaas69
    Prodigy 40 points

    we use ina240 for measuring the phase current of the motor. we use 48V level dc bus voltage, and using the gate driver, we control the pwm of the power. usually our motor's resistance is about 1 ohm and its inductance is about 100 uH level. 

  • 0 in reply to Jaesung Oh
    Guru 140200 points

    Hi Jaesung,

    the scope plot seems to show several yellow traces which lie on top of each other? Can you set a suited trigger level so that we can see only one trace? And can you speed up the horizontal deflection to 1µs / div or 2µs / div?

    Jaesung Oh said:
    usually our motor's resistance is about 1 ohm and its inductance is about 100 uH level

    Whenever an inductance is involved, inductive kickback can occur which may violate the absolute maximum ratings of common mode input voltage. So, we would need to see a scope plot of the input signal of INA240 as well.

    Kai

  • 0 in reply to kai klaas69
    TI__Mastermind 34240 points

    Hi Jaesung,

    Other than the scope shots Kai requested, can you please monitor the common mode voltage as well? Is the power supply stable during the test?

    As precaution, is the NC pin shorted to ground or left floating?

    Regards, Guang