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TMS320F28379D: ADC sampling transition

Bruce(Shanghai) Liu
Intellectual 1010 points

Part Number: TMS320F28379D
Other Parts Discussed in Thread: LAUNCHXL-F28379D, TMDSCNCD28379D

The problem is shown in the figure. Red, green, and blue are three current samples, and the AD ports corresponding to ADCC, ADCD, and ADCA are used to sample respectively. It can be seen that the green (ADCD) sampling data often jumps. Corresponding to the change of the AD value, there will be a 40-unit jump (ADCD) in the AD value. The measured ADC input voltage has no jump.

It should be noted that only ADCD will have this problem. When the sampling signals of ADCD and ADCB are exchanged, ADCD sampling still has a jump (the settings of ADCB, ADCC, ADCD sample hold time, etc. are exactly the same). Customers are curious about whether there are differences in the ADCB, ADCC, and ADCD designs inside the chip .

  • 0
    TI__Intellectual 1010 points

    One thing needs to be added, the customer's ADC voltage reference uses REF3030 to directly connect to the 4 voltage reference pins, without RC filtering and buffer. However, there should not be such differences between different ADC groups

  • 0 in reply to Bruce(Shanghai) Liu
    TI__Guru 62975 points

    Bruce,

    There is no figure attached so we are not able to see any of the referenced signals.

    Are you indicating that a single REF3030 is driving all four ADC references without the recommended buffering or required bypass capacitance? The SAR ADC architecture requires a very clean reference voltage with the ability to meet instantaneous inrush current needs of the internal sampling capacitors.

    Can the same ADC configuration and sampling be tried using a TI EVM (LAUNCHXL-F28379D or TMDSCNCD28379D) to see if the issue is present? The EVM would serve as an example of acceptable handling of the ADC reference voltage.

    Are the ADC operating synchronously as described by the datasheet and TRM?

    -Tommy

  • 0 in reply to tlee
    TI__Intellectual 1010 points

    Hi Tommy,

    Thanks for your reply. Yeah, the ADC is operating synchronously as described by the datasheet and TRM. The figure is shown as follow.

  • 0 in reply to Bruce(Shanghai) Liu
    TI__Intellectual 1010 points

    The issue can't be reproduced by using a TI EVM (LAUNCHXL-F28379D or TMDSCNCD28379D), because there are many functions that EVM does not have  

  • 0 in reply to Bruce(Shanghai) Liu
    TI__Guru 62975 points

    Bruce,

    We will want to reduce our focus down to a minimum set of variables. It is very difficult to remotely debug a custom application that is handling concurrent activity.

    If possible, we should reduce the experiments down to just sampling a static input voltage using the ADC as configured for the target application. This way, if the issue remains, we can focus only on the ADC and even try to reproduce the problem on the EVM.

    -Tommy