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ADS7049-Q1: ADS7049-Q1

SERRE Laurent
Prodigy 10 points
Part Number: ADS7049-Q1

J’ai une question technique sur l’ADC référence ADS7049-Q1 de Texas Instruments, qui est la suivante :

Peut-on faire planter un ADC en lui envoyant des mauvaises commandes sur son bus SPI ?

Les conditions d’utilisation sont les suivantes :

1°) Acquisition :

  • Nombre d’acquisition = 8 de durée de 16μs chacune (soit une durée totale d’acquisition de 128μs)
  • Fréquence d’acquisition : toute les 25ms
  • Chip Select (/CS) :
    • à l’état 0 pendant l’acquisition (128μs)
    • à l’état 1 pendant le reste du temps (24,872ms)

2°) Perturbations :
Les 3 signaux du bus SPI (SCLK, /CS et SDO) peuvent être perturbés pendant du démarrage du convertisseur de puissance

  • Si commande du μP = 0 => Signal vu par l’ADC peut passer à 1 pendant la perturbation (durée = 50ns)
  • Si commande du μP = 1 => Signal vu par l’ADC peut passer à 0 pendant la perturbation (durée = 1μs)

Est-ce que l’ADC va redevenir fonctionnel après la perturbation ? Est-ce que la prochaine acquisition (qui arrivera 25ms plus tard) sera correcte ?
Ou faut-il couper ses alimentations, puis le remettre sous tension afin de le refaire partir proprement ?

Cordialement,

  • 0
    TI__Mastermind 18367 points

    Serre,

    I used google translate to convert your question to English.  I believe that I understand the main point of the question.  The only possible corruption that can happen to the ads7049-Q1 is the offset calibration register.  Normally, the offset calibration register is set to zero during power up.  If some unusual event happened during power up that corrupted the offset calibration register, you could do an "offset calibration during normal operation".  You can calibrate the offset by clocking SCLK 32 times with CS low.  Other than the offset register, no other issue should happen as the device is "read only" and the only volatile "register" is the offset calibration.

    I hope this helps and that Google translate worked.  

    Art 

  • +1 in reply to Art Kay
    Prodigy 10 points

    Hello Mr Kay,

     

    In our application:

    • We do a calibration after each power-up
    • We have the possibility to test the calibration (by measuring a reference voltage)
      • If the calibration test is OK => We launch the acquisitions
      • If the calibration test is NOK => We will redo the calibration (according to your advice) until the calibration test becomes OK

     

    Then in our application:

    • A bad transient acquisition is not a problem (because we have a filtering of the measurements)
    • However a bad permanent acquisition would be embarrassing

    Can you confirm that perturbations (EMC interferences) on the /CS and SCLK signals, has no risk of inducing a permanent malfunction of the ADC reference ADS7049-Q1?

     

    Regards

  • 0 in reply to SERRE Laurent
    TI__Mastermind 18367 points

    Serre,

    We have not done any EMC testing on this device.  Our experience with similar devices is that during radiated immunity tests the device may have a temporary loss of performance and will return to normal operation afterwards.  In some cases, the device will maintain operation during the immunity test.   Here is a link to EMC testing done on an ADC https://www.ti.com/lit/an/sbaa548a/sbaa548a.pdf.  I really cannot comment on permanent malfunction of this particular devices as we have not tested it.  Even if we did test this device, the PCB layout and support components will impact EMC test results, so we recommend that you test your system.  Also, it depends on the EMC test (radiated immunity, EFT, surge) and the test levels as to how the device performs.  Nevertheless, if your concern is radiated immunity on the digital interface, I do not expect this to cause permanent malfunction of the device.  

    Art