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Original question:

TIDA-01421: obtain an unknown signal from launchpad

TIDA-01421: Obtain a signal when driving motor with relays

Gunjan Nagpal
Prodigy 90 points
Part Number: TIDA-01421
Other Parts Discussed in Thread: INA240

Hello!

I am trying to control a motor on a car’s sunroof for a project. For this, I am using the TIDA-01421 reference design. I have attached the circuit that I am using.

But I am not able to get any result on an oscilloscope. I have set the sensing probe of the oscilloscope on the timer pin and the ground of the probe with the ground of the motor/power supply. The motor is rated for a maximum stall current of 18A and draws around 2A when running with a power supply. I am not sure what I am doing wrong here since I don’t really have a strong background in electronics. I was hoping that someone could provide some insight.

Thanks in advance!

  • 0
    TI__Expert 3875 points

    Gunjan,

    Could you post a scope image of the analog signals, starting with the motor current on the right side of R6 w.r.t. ground?  That will be a small ripple current on the 6mV (2A x 3 mOhm) voltage.  Better if you can capture the signal at U2 pin 5, which is the output of the first gain stage when the motor is running.

    I'm assuming the relay should not have any significant impact on the signals.

    By the way, the manner  in which you have the connections makes it look like you can only drive the motor in one direction.  That seems odd for a sunroof.

  • 0 in reply to Clark Kinnaird
    Prodigy 90 points

    Hello Clark,

    Thanks for your reply. I tried to get a good image on the oscilloscope, but I am not sure if these are the right readings or not...

    Signal at right side of R6 w.r.t. ground

    Signal at pin 5 of U2 w.r.t. ground

    I removed the relays from the circuit in order to reduce uncertainties. I was using two relays, one for forward and the other for backwards motion, but now it's just connected to the power supply directly.

    Thanks and regards,

    Gunjan

  • 0 in reply to Gunjan Nagpal
    TI__Expert 3875 points

    Gunjan

    The trace on the sense resistor (R6) looks like typical motor ripple, with 100 mVpp amplitude and frequency about 1.3 kHz.  But the output of the INA240 (U2-5) does not show the amplified signal.  U2-5 is correctly at half of the 5V supply, but it should also have the amplified ripple.  I would concentrate your debug on that stage first.  It is acting like it is not connected to the voltage across R6.

    -Clark