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ADS1256: How to obtain higher throughput (output data rates) when multiplexing multiple channels

Part Number: ADS1256

Hi Chris,

Even though my ADS works great with the microcontroller, I was not able to cycle through 6 channels more than 600Hz. The biggest reason is that I have to mux between channels; and everytime I do so, I also have to send SYNC and WAKEUP Commands.

I wonder if it is possible to do the following:

1. I can replace the XTAL clock 7.68MHz on the board by a 10Mhz one.

https://www.sparkfun.com/products/535

https://www.ebay.com/itm/ABRACON-10MHz-Crystal-ABL2-10-000MHz-D4Y-T-HC-49US-Qty-20/181206608409?hash=item2a30c16a19:g:vB0AAMXQILVSILvL

2. I run the SPI speed at 5Mhz (half of the oscillation frequency

Ideally, I probably be able to increase the sampling rate to 800Hz. what else could I do?

Thanks,

Khoi Ly

  • Hi Khoi,

    Increasing the fCLK and SCLK frequencies are the only things that will give you a bit more throughput while multiplexing with this ADC.

    Looking at table 14, you can estimate the data rate while mux'ing. Divide that number by 6 channels and it will give you the effective data rate per channel. At 30,000 SPS, the cycling throughput is 4374 Hz, or 4374/6 = 729 Hz/channel for 6 channels.

    Therefore, to achieve 800 Hz/Channel, you will need an fCLK of about (800/729) * 7.68 MHz = ~8.5 MHz. A 10 MHz fCLK and 5 MHz SCLK should certainly be fast enough to provide you with 800 Hz/channel for 6 channels. Note that the 30,000 SPS data rate will actually be (10/7.68) * 30,000 = 39,062.5 SPS with the 10 MHz clock.