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ADS1296R - DRDY timing error

Arun Kumar27
Intellectual 590 points
Other Parts Discussed in Thread: ADS1296R, MSP430BT5190, ADS1296

Hi,

I am using ADS1296R in a custom board with MSP430BT5190.

I have configured ADS1296R to use internal oscillator. It was working fine for few days.

But then i started receiving fewer samples in a second i.e) for 250SPS setting i am getting only 216(sometimes 217) samples.

I observed DRDY signal on scope, for 250SPS  i should get a DRDY every 4ms, but i am seeing 4.6ms delay between each DRDY.

1. Is it oscillator fault? if so, what might be the cause?

2. Is there any way i can correct this or replacing the chip is the only solution?

Thanks 

Arun

  • 0
    TI__Mastermind 38745 points
    Hey Arun,

    That does seem to be outside of specification for the internal oscillator. Can you post your schematic so I can see if I can find the source of the problem?

    Regards,
    Brian Pisani
  • 0 in reply to Brian Pisani
    Intellectual 590 points

    Hi Brian,

    Please find the schematics of ADS1296 and Controller interface.ads_mcu.pdf

    Out of 25 prototype boards, 2 boards are showing this problem. Note that these boards worked fine initially for few days, then started giving this issue.

    Please suggest if any changes are required.

    Thanks 

    Arun

  • 0 in reply to Arun Kumar27
    TI__Mastermind 38745 points
    Hey Arun,

    It looks like you are in control of the CLKSEL pin. Is that pin asserted so that you are using the internal oscillator? Otherwise the CLK input is also connected to the host which means that device is responsible for providing timing to the ADS1296.

    Regards,
    Brian Pisani
  • 0 in reply to Brian Pisani
    Intellectual 590 points
    Hi Brian,

    Yes I am asserting CLKSEL pin to enable internal oscillator.

    Following are the couple more checks i did.
    1. Enabled CLK_EN bit of Config 1 register to output the internal clock on Terminal 8G and observed it on scope.
    Good board - 2.05MHz
    Bad board - 1.76MHz
    2. Enabled external clock by making CLKSEL low. The board works fine.

    Thanks
    Arun
  • 0 in reply to Arun Kumar27
    TI__Mastermind 38745 points
    Arun,

    Interesting. I'm not sure what could have been causing that before. Had your microcontroller pin which was connected to the clock output ever been configured as something other than high-z?

    Brian
  • 0 in reply to Brian Pisani
    Intellectual 590 points
    Hi Brian,

    There are only two ways i have configured CLK output pin from controller (external clock to ADS)

    1. Internal oscillator mode for ADS -
    In this case, this pin i.e) P11.2 (SMCLK from MSP connected to ADS as external clock) is left to the defaults

    But this does not affect ADS in any way because, during this mode the 0Ohm resistor between 8G (CLK) pin of ADS and P11.2 (SMCLK of MCU) is not placed so that they are not connected.

    2. External CLK mode for ADS -
    In this case, i have placed that 0Ohm resistor to connect 8G pin from ADS to P11.2 (SMCLK) of MCU.
    Configured P11.2 peripheral function port(enabled P11SEL.2),
    configured it as output( enabled P11DIR.2)
    And Pulled down the CLKSEL pin of the ADS to enable external clock.

    Thanks
    Arun
  • 0 in reply to Arun Kumar27
    TI__Mastermind 38745 points
    Hey Arun,

    How many boards exhibit this phenomenon and how many do not? If it's not consistent then it could have been damaged at some point.

    Brian Pisani
  • 0 in reply to Brian Pisani
    Intellectual 590 points
    Hey Brian,

    I forgot to mention that in previous post, out of 24 boards, 2 are exhibiting this issue.

    One more fact is that, both these devices were in India for some time and were working fine. Then we shipped these two to US with two more devices. In US they worked for some time and then these two out of 4 started showing this issue.

    I don't know how relevant this is, but i just don't want to leave any stone.

    Thanks
    Arun
  • 0 in reply to Arun Kumar27
    TI__Mastermind 38745 points
    Hey Arun,

    My best guess (since I have no other legitimate theories) is that the devices suffered some ESD damage during packing or shipping which caused a gradual degradation in performance. If it happens to more devices, let me know so we can look at other possible causes.

    Regards,
    Brian Pisani
  • 0 in reply to Brian Pisani
    Intellectual 590 points

    Hi Brian,

    In the board we are using an ESD protection IC - ZL70584UDJ2E from microsemi, each of the ecg leads coming from body is also connected to one of the terminal of this IC.

    Wouldn't this chip take care of the ESD you mentioned?

    Thanks

    Arun

  • 0 in reply to Arun Kumar27
    TI__Mastermind 38745 points
    Hey Arun,

    That would protect the analog inputs pretty well but the digital pins would still be exposed to ESD. I'm not saying conclusively that is what happened, I'm just saying that might explain it unless you see the issue across a more significant number of devices. Whatever caused it, the problem seems anomalous rather than systematic.

    Brian
  • 0 in reply to Brian Pisani
    Intellectual 590 points

    Hi Brian,

     Thanks for quick responses.

    Will post if i observe anything else further.

     Arun

  • 0 in reply to Arun Kumar27
    Intellectual 590 points
    Hi Brian,

    If it is due to ESD, what is the possible means of protecting ADS1296 from it?

    Arun
  • 0 in reply to Arun Kumar27
    TI__Mastermind 38745 points
    Hey Arun,

    I can't be completely sure that's what caused it, but the means of protecting it from ESD damage are the same sorts of things you'd do for any other IC. Wearing a grounded wrist strap of ESD dissipative surfaces when working with sensitive electronics is advised. Storing/shipping devices in ESD bags and special ESD packing material is also highly recommended.

    Regards,
    Brian Pisani