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CCS/ADS1274: SPS and Discrete mode

Joonbum Kim45
Intellectual 310 points
Part Number: ADS1274
Other Parts Discussed in Thread: TMS320F28379D

Tool/software: Code Composer Studio

According to the data sheet, maximum data rate is 144kSPS @ high-speed mode(fclk=37MHz).

Does it mean 144kSPS/channel or total 144kSPS(36kSPS/channel)? 

What is the maximum sampling if I use all 4 channels?

How do I use discrete mode?

Is there any example to reference? (MCU, HW wiring, Code, etc.)

  • 0
    TI__Mastermind 37690 points

    Hello Joonbum,

    The ADS1274 has 4 individual ADC cores inside the device.  Each ADC simultaneously samples the input.  The maximum output data rate for each channel is 144kSPS.  There is no reduction in throughput per channel based on the number of enabled channels.

    Another way to state this; if all 4 channels are used, you will get a total of 4x144k= 576000 conversion results in a 1 second period.

    All of the configuration settings for the ADS1274 are set by connecting hardware pins to high or low.  To set the device to discrete mode using the Frame-Sync Interface protocol, you would connect FORMAT1 (pin 31) to ground and FORMAT2 (pin 30), FORMAT0 (pin 32) to IOVDD.  This will enable Frame-Sync mode which uses the SCLK and FSYNC pins, along with DOUT1, DOUT2, DOUT3 and DOUT4 pins, as shown in Figure 80 of the datasheet.

    The ADS1274 also support the SPI protocol.  However, in SPI mode, the maximum CLK freqency is reduced to fclk=27MHz.  This limits the maximum output data-rate of each channel to 105.5kSPS.

    We do not have any example code for this device.  However, if you have a specific mode that you want to configure the device, I can provide a list of the correct pin connections.

    Regards,
    Keith Nicholas
    Precision ADC Applications

  • 0 in reply to Keith Nicholas
    Intellectual 310 points

    Hello Keith,

    Thank you for the excellent answer.

    As a further question, I'm curious about the connection on the MCU side of discrete mode.

    Do I have to connect with DMA? or 4-SPI(FSYNC)?

    Thank you very much.

  • 0 in reply to Joonbum Kim45
    TI__Mastermind 37690 points

    Hi Joonbum,

    I am not sure what hardware resources you have on your host MCU.  However, for discrete mode using SPI, you will need a single SCLK and 4 MISO inputs on your MCU.  You will also need to monitor the DRDY line (either software poll or hardware interrupt) to start the transfer for each conversion cycle.

    If your MCU is fast enough relative to the sample rate, you may not need to use DMA, but if you have it available, it will free up more cycles on your processor to perform other tasks.

    Regards,
    Keith

  • 0 in reply to Keith Nicholas
    Prodigy 30 points

    Hi. Keith.

    I am glad to see you in this forum.

    I am working with Joonbum ^^ and a HW engineer.

    Thanks for your response for Joonbum's questions.

    According to your answer as below,

    'you will need a single SCLK and 4 MISO inputs on your MCU'

    This mean is we should choice the MCU which must have 4 SPI, am I right?

    Now we consider TMS320F28379D for ADS1274 but this DSP only has 3 SPI.

    then we should change to other DSP? If we can use 28379D, Please inform how to connect ther DOU1~4.

    If we should change the DSP, Please recommend the DSP for 4CH SPI that should have higher or same performance as TMS320F28379D.

    Thank you.

  • 0 in reply to Youngman Kim
    TI__Mastermind 37690 points

    Hello,

    Since your MCU does not support 4 SPI channels, I suggest using the TDM mode which will only require 1 SPI port.  Each SPI frame will transfer a total of 4x24=96 bits for the 4 channels. 

    Please refer to figure 78 in the datasheet.  This will require an SCLK frequency of 96x105500=10.2MHz. 

    To get best performance, run SLCK at either 1/2 of CLK or equal to CLK, which would be 13.5MHz or 27MHz.

    Regards,
    Keith