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ADS8556 Sampling and TMS320F28335

hongqi Ting
Prodigy 10 points
Other Parts Discussed in Thread: ADS8556

Dears,

I use DSP F28335 to expand ADS8556. When sampling, the input signal will produce many spikes, which will affect the sampling; In addition, signals between channels will also affect each other. For example, CH1 has an input signal and CH2 has no input signal. After sampling, ADC can read not only the value of CH1, but also the value of non-zero CH2, which fluctuates greatly. I want to know what causes this result.

This spike will appear every time when starting the ADC conversion.

  • 0
    Expert 1786 points

    Hi,
    I belive the problem is due to lack of the capacitance on the inputs of the ADC.
    When conversion is initiated the internal sample-and-hold circuit charges the internal capacitance (10 or 20pF according to datasheet), and if there is no charge reservoir on the inputs of the ADC then there will be voltage drop on the inputs. In the datasheet of the ADS8556 this is described. The signal source has to be low impedance also. Look in the "8.2.2 Detailed Design Procedure" chapter and the "charge injection damping circuit".

    Regards,
    Andy

  • 0 in reply to AndyP
    Prodigy 10 points

    Thank you for your reply. As you rightly say, we have solved the problem！Handshake

    Best regards,

    Hongqi