Dual MC33887 current feedback problem

I using the dual MC33887 motor driver and I have problems with its current feedback which is suppose to give me 0.59 V/A, however I get different ratios for different loads (0.35 at 0.2A, 0.45 at 1A, 0.53 at 1.5A, 0.59 at 2.5A) and I don’t understand if my kit is damage or I have something wrong in my connections.
My connections are:
D2=PWM input (1Khz-10Khz), IN1+EN=3.3v-5.0v, IN2+D1+FS=disconnected.
I need help since my application is very sensitive to the feedback sensor value.

Hello,

In general, the current measurement is not very accurate, and I think your results are within the expected range for these things (you can see in the datasheet that the feedback accuracy is worse at lower currents and around ±25% at 0.5A). One thing to check is how you’re making your measurements. If your current is not DC (e.g. you’re PWMing at a low duty cycle), you could get misleading readings fairly easily.

We’ll be coming out with a more precise current sensor later this month, so that might be something you can consider for improving your system.

- Jan

Thanks Jan

-Is the PWM freq. had an affect on the current sensor (How can I improve the current sensor feedback to remains around the typical value?).
-What is the best method for measuring the effective voltage and current of a PWM (DC components)?

Thanks again and Keep up the good work.

Can you look at the current sense line on an oscilloscope? I was just wondering how you measured your current and feedback voltage in the first place since it’s possible that those measurements were adding to your error. In general, you should average a lot of samples, and you should make sure that your sample rate is high compare to the PWM frequency. You could also put a bigger cap on the feedback line to smooth it out more (the oscilloscope would be handy there to see what you’re doing to the signal).

- Jan