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INA293A4 weird waveforms.

Other Parts Discussed in Thread: INA293

Hi, I am trying to use INA293A4 as current signal amplifier hi side aplication with 24V Vcc, 2mR Rsens and 3,3V supply for cycle by cycle current limiting in DC/DC buck converter. Firstly at starting up the board I set frequency to 100kHz an set constant PWM at 25% and watch waweforms, which are weird for me. Please take a look at it and tell me if it should work as it is?

Brown - Inductor current

Green - INA output

Yellow - PWM

Then I set PWM at about 80% and this is the waveforms:

After that I increase sens resistor to 10mR and changed INA293A4 to INA180A1, and wawefoms look wery similar. 

Here is the layout:

I was expected fast clean response but get more than 1us delay and slow falling response.

Am I doing something wrong?

  • Hello Marcin, 

    I believe you are hitting a limitation of the INA293 and most CSA with unidirectional current sensing.  If the input is going to zero output voltage you could be saturating the input stage and the device is no longer operating in the linear range.  When this happens the device does not recover as soon as the input gets back to a linear range and it must get out of the saturation point.  One way to avoid this is to add a resistor to the In- something like a filter resistor.  This will induce a positive offset.  The tradeoff is getting offset error and gain error induced by the resistor.  Also the resistor cannot be large as the input bias current does change with the differential voltage.

    The other limitation of the INA293 is the lower bandwidth vs Vsense voltage as seen in the datasheet.

    Besides the options above you could attempt to use a bipolar device that will not get into saturation.  

    The above may bring more questions please let me know if I can answer any additional questions you have.