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INA333: Sawtooth waveform

Marvn Arcangel
Genius 16680 points

Part Number: INA333

Hi experts, 

Need advice on this one.

b3144ff3c33e15718813dc3d8a672b79 (1).png

The simulation shows straight line but when the circuit was built, the output showed a sawtooth waveform instead. What could be the issue?

f889f4e334f8076ffbaad7baf1a534eb (1).png

More information:

1. The oscilloscope probe I used is standard lenght.
2. There are no long wires between the output point and the measurement terminal; the oscilloscope probe is connected to the output point via a 5 cm wire.

Regards,

Marvin

  • 0
    TI__Intellectual 1980 points

    Hi Marvin,

    I would first check what the inputs of the INA look like to see if they are DC voltages. Also, is the node circled below a correct connection point?

    One thing that I do notice about this schematic is that the reference is not buffered. If the REF pin of an INA sees a large input impedance, the CMRR of the device can degrade significantly as explained in this section of the datasheet. 

    If there is significant ripple on any of the voltages sources above, you can see ripple on the output, especially VG1 due to CMRR degradation.

    Could you measure if there is any ripple seen on any voltage sources? Also, if you create a low impedance connection on the REF pin to GND, does the issue persist?

    Best Regards,

    Taylor Allan