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ADS8555: I am considering ADS8555 for our application, and have some questions about PSRR:

EEngineer505
Prodigy 590 points
Part Number: ADS8555
Other Parts Discussed in Thread: ADS8568, TPS65131, ADS8588S

Hello,

I am considering ADS8555 for our application, and have some questions about PSRR: 

  1. Datasheet does not list a PSRR spec for HVDD, HVSS.  On page 35, “The high-voltage supplies (HVSS and HVDD) are connected to the analog inputs. Noise and glitches on these supplies directly couple into the input signals.”  Does this imply 0dB PSRR?  Our power conversion designer is proposing 1MHz converter with ferrite beads and usual capacitive bypassing.

  2. Datasheet figure 10 on page 15 plots PSRR at fdata=maximum (630kSPS?), 60dB.  Our application sample rate is 7.8kSPS.  What is PSRR with this sample rate and 1MHz AVDD noise frequency?


Thank you for your help.


  • 0
    TI__Mastermind 35550 points

    Hello EEngineer505,

    Thanks for choosing our HV SAR ADC in your application, here are answers to your questions:

    1. It doesn't mean that 0dB PSRR for HVDD and HVSS, we only didn't characterize this spec.

    Actually the DC-DC converters have been used a lot to provide suppliers directly to our SAR ADCs, as an example on ADS8568EVM board, TPS65131 is used to create HVDD(+12V) and HVSS(-12V) high voltage supplies to ADS8568 which is a 16-bit SAR ADC similar as ADS8555 but ADS8568 has 8 channels. TPS65131 is a DC-DC converter and its switching frequency is 1.38MHz(min-max: 1.25~1.5MHz), this power solution does NOT degrade any ADS8568's performance which has 91.5dB SNR. ADS8568EVM schematic TPS65131 datasheet are shown in below two website links.

    http://www.ti.com/general/docs/lit/getliterature.tsp?baseLiteratureNumber=sbau193&fileType=pdf

    http://www.ti.com/general/docs/lit/getliterature.tsp?genericPartNumber=tps65131&fileType=pdf

    If 200ksps sampling rate can meet your design requirement, ADS8588S only requires single +5V power supply but support +/-10V and +/-5V bipolar direct input with best performance in the market, its PSRR is about -150dB at 1MHz frequency shown in Figure 89 of datasheet and as below.

    http://www.ti.com/product/ADS8588S

    2. I will check if we have any data for PSRR with 1MHz noise frequency on AVDD related to ADS8555, and will let you know soon. 

    Thanks.

    Best regards

    Dale Li

  • 0 in reply to Dale Li
    TI__Mastermind 35550 points
    Hello EEngineer505,
    After checked 2nd item listed above, unfortunately we don't have any data for PSRR with 1MHz noise frequency on AVDD related to ADS8555. Thanks for your query.

    Best regards
    Dale Li