• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 45 subscribers
  • Views 532 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS8688: Hardware Questions About ADS8688

user5138588
Prodigy 20 points
Part Number: ADS8688


Hi,

We'd like learn some details about ADS8688. For an over current protection mechanism, we're planning to integrate the ADS8688 as main ADC converter, it will measure AC signals for 50/60 Hz and we have to capture every period of the signal precisely. Sampling rate is relatively low, about 7.6 kSPS, for this sampling rate; we will use an external clock/trigger module.

We're carefully examined the datasheet, to be sure, we've a few questions :

    - Is the SPI output behave like FIFO buffer? Can we read all sampled data after a cycle?

    - Can we do the same job without an external clock? ( Automatic mode? )

    - Is there any resolution difference if we use +/-10V or +/-5V as voltage reference?

    - Is there a problem if AUX_IN pin is connected to GND?

Regards,

Gokhan

  • 0
    TI__Mastermind 46135 points

    Hi Gokhan,

    - The simple answer is no, you can not do that. The conversion data will be shifted to SDO after receiving 16-bit data on SPI during each cycle(either 0x0000 for Continued Operation or other command for Manual Ch Selection). Each cycle or conversion needs 32 SCLK clocks. The Auto CH Sequence mode can be selected with 0xA000 command so that there is no need to send Manual Ch Selection command for every conversion, also each channel can be individually enabled or disabled in AUTO_SEQ_EN program register.

    - See my answer above.

    - When the input range is +/-10V or +/-5V (+/-2.5Vref or +/-1.25Vref, the reference voltage is same 4.096V), most specifications are same only except few slightly different specifications: Offset error(typ is same, max +/-0.75mV vs +/-1mV), offset matching and SNR (92dB vs 91dB typ). When I tested on EVM board, I did not significant difference between these two input ranges.

    -  No. AUX_IN is always recommended to connected to the GND when it is not used.

    Please let me know if you have further question.

    Regards,

    Dale

  • 0 in reply to Dale Li
    Prodigy 20 points

    Hi Dale,

    I didn't understand, do you mean we have to send a query for every read operation? Is there any way to trigger it for a "constant" time? If not, do you have any other recommendation for this purpose?

    Regards,

    Gokhan

  • 0 in reply to user5138588
    TI__Mastermind 46135 points

    Hi Gokhan,

    Please check the timing diagram in Figure 1 in ADS8688 datasheet. The ADC needs 32 SCLK clocks for conversion and data reading for each channel, you can not read all sampled data after a cycle. There is no internal FIFO or memory to save the conversion data.

    Thanks&Regards,

    Dale