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ADC121S021: CS/ Pin Behavior

PY (Pengyu) Song
Expert 5860 points
Part Number: ADC121S021
Other Parts Discussed in Thread: ADC122S051, ADC101S021

Hi team,

Will ADC121S021 continue to do conversions when CS/ pin is low? 

Another 2-ch device ADC122S051 has below description stating that conversions continue as long as CS/ pin is low. 

Thanks. 

  • 0
    TI__Mastermind 22950 points

    Hi PY,

    For the ADC101S021, the conversion time is determined by the number of SCLK cycles and the SCLK frequency. Please take a look at Figure 1 in the data sheet. 


    Regards,
    Aaron Estrada

  • 0 in reply to Aaron Estrada
    TI__Expert 5860 points

    Hi Aaron,

    Then I will assume conversions will continue when CS/ pin is held low, and it will only depend on SCLK - is this correct? Please note in Figure 1 CS/ pin does go to 'high' after 16x clocks. 

    Again, what I want to ask is if CS/ pin is permanently held low, will ADC101S021 continue to do conversion as well as output SDATA as long as SCLK clocks? 

    In comparison, ADC122S051's datasheet has clearly stated above can be done with CS/ pin is held low. 

  • 0 in reply to PY (Pengyu) Song
    TI__Expert 5860 points

    Hi Aaron,

    Any update? 

  • +1 in reply to PY (Pengyu) Song
    TI__Mastermind 22950 points

    Hi PY,

    Your first point about the conversion depending on SCLK are correct.

    Regarding the CS being permanently held low, the device will have nothing to convert if CS is permanently low. The acquisition time is the time used to charge up the internal sample and hold capacitor. This time starts on the 13th rising clock edge and ends on the falling edge of CS. If CS is permanently low, then the falling edge never happens. Therefore, the device will only be acquiring. If the device is in an 'acquiring' state, then there will be no conversions. 

    Regards,

    Aaron Estrada

  • 0 in reply to Aaron Estrada
    TI__Expert 5860 points

    Hi Aaron,

    Thanks for your explanation. Per your explanation, I suppose 1-ch ADC121S021/ADC101S021 is unable to do conversion continuously when CS/ pin is held low permanently. 

    In comparison, 2-ch ADC ADC122S051 has stated that the device is able to do conversion continuously as long as CS/ pin is held low. Based on timing diagram, it seems ADC122S051 can enter power down mode in every 16 clocks even though CS/ pin is held low, which results in continuous conversion operation when CS/ pin is held low. 

    Can you please advise if there is any 1-ch ADC device has similar feature as 2-ch ADC ADC122S051 that can perform continuous conversion without toggling CS/ pin? 

  • 0 in reply to PY (Pengyu) Song
    TI__Mastermind 22950 points

    Hi PY, 

    What other device features are you looking for? Is there a need for a specific sampling rate, number of channels, type of ADC (SAR or Delta-Sigma), resolution, etc.?

    I know we have the ADS101x and ADS111x family have have a continuous conversion mode but these are delta-sigma ADC and not sure if they will fit the necessary requirements. 

    Regards,
    Aaron Estrada