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Regarding ADS1230 REF Low Pass Filter

Jayaraj A
Prodigy 200 points

Other Parts Discussed in Thread: ADS1230

Dear Sir,

       In my previous mail, I had raised a query regarding ADS1230 reference, consider this post as a extension to that.

On what basis/formula, in your reference design, you had designed the LPF on ADS1230 REFP & REFN? (100E, 100uF & 2.2uF) what is the Cut-off region in terms of Hz?

I am using the inbuilt 76.8KHz Modulator frequency, so how to relate the LPF design(cut off freq) of ADS1230 REFP & REFN with the 76.8KHz switching capacitor?

this LPF design is to avoid the noise from other parts of board to enter the REFP& REFN or from REFP& REFN to other parts?

With regards

jayaraj.a

  • 0
    TI__Guru** 113765 points

    Jayaraj,

    Unfortunately the person that designed the ADS1230REF no longer works for TI, so I can't tell you for sure why certain values were used.  The general equation for a low pass filter cut-off frequency is: fc = 1/(2*pi*R*C).

    One thing to keep in mind is if you heavy filter the reference because AVDD is noisy, but AVDD is the excitation to the bridge, then you will measure the noise along with the desired bridge output signal.  It would be better to filter AVDD before being used as the excitation voltage, and then use the same filtered output connected to the reference input as well.  You could also use a 0.1uF cap close to the input pins to the reference.

    Best regards,

    Bob B