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AM4379: ADC1 crosstalk in single-end use case

kent lu
Prodigy 230 points
Part Number: AM4379


Hi TI experts,

I'm using ADC1 on AM4379 to realize a general A/D function(8 channels are all needed), and I got below information from Technical Reference Manual(SPRUHL7H):

However, the effect of the bias resistors and bias supply on the attached voltage source(s) should be considered when using ADC1 as a general purpose ADC. Each internal bias supply has a high output impedance when turned off which will be the case when bypassing the preamplifiers. In this use case, the majority of the input leakage current from any of the analog inputs will be based on the external voltage source connected to the other input associated with the preamplifier. For example, the ADC would measure 0.975 volts on ADC1_AIN1 if it were connected to a 1.0 volt, 1 kohm source while ADC1_AIN2 is connected to a 0.5 volt, 1 kohm source. The error caused by the internal bias resistors can be minimized by connecting the analog inputs to low impedance voltage sources or leaving the other input associated with the preamplifier open-circuit.

Does it mean, if ADC1 is configured as single end mode, the cross talk issue can not be avoided?  Then could you advise a good way to improve the accuracy? thanks.

Kent Lu

 

  • 0
    TI__Guru 63145 points

    That is correct. The leakage must be considered when you design your system. The output of each source connected to one of the ADC1 inputs needs to be able to source or sink any leakage current as required to achieve the desired accuracy.

    Note: We recently found other leakage paths from VDDA to each input via the ADC preamp, where each input may have as much as 40uA of leakage from VDDA.  So you also need to account for this leakage along with the leakage already described in the TRM.

    Regards,
    Paul