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ADS8698: Read data rate issue

Rock Su
Intellectual 2220 points

Part Number: ADS8698

Dears,

The MCU is: STM32F103, ADC: ADS8698.

According to the datasheet the maximum throughput is 500Ksps, they are using hardware SPI, the SCLK used is 18MHz, The function they encapsulated is 8bit every time it is sent and read, so a total of 16bit is written to the ADC. 24bit is used for reading, and the CS pin is measured by an oscilloscope. The time for completion of CS pulling down and then pulling up is: 8.2us. They use 8 channels here, so the time for one round of use is: 8.2*8= 65.6us, then the overall throughput is: 1000000/65.6=15243, which is equivalent to the overall throughput: 15KSPS, so they don’t know where the time is used?

Best Regards,

Rock Su

  • 0
    TI__Mastermind 48025 points

    Hi Rock,

    To be clear, the /CS signal shown in your first timing screenshot is controlled by the customer's microcontroller, this /CS signal is actually a conversion start signal for the ADC and the falling edge of /CS will trigger a data conversion, the actual sampling rate of the ADC depends on the /CS given by the microcontroller.

    The required minimum time for a conversion and data reading is:

    tCONV + tACQ = 825ns + 1175ns = 2000ns which is a corresponding 500ksps sampling rate.

    The /CS low pulse time your customer is sending to the ADC is much longer than the requirement. Hence, the sampling rate on the ADC is reduced. If a higher sampling rate is desired by the customer, they should shorten the time interval of low /CS.

    Best regards,

    Dale Li