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ADS1292R : Quries on RESET and RLD

Mahendra Patel1
Expert 3560 points
Other Parts Discussed in Thread: ADS1292R

Hello Team,

I have got couple of queries on ADS1292R,

1. To reset the device during power up, will SPI module of ADC be functional (during POR time) to RESET the device through SPI interface,

or this is possible only when ADS1292R device is powered up.

2. If RLD lead is not there in Electrode, is there a way to improve CMR (it’s a battery operated design) ? Is it always necessary to use RLD for ECG. If yes, what are options to implement?

Regards,

Mahendra Patel

 

  • 0
    TI__Guru 66466 points

    Hello Mahendra,

    Thank you for your post!

    1. Either the SPI command or the /RESET pin can be used to reset the ADS1292R after tPOR.
    2. In this application, are the electrode inputs AC coupled? Typically, if a 3rd electrode is not available for the RLD, the electrode inputs are AC coupled and the DC bias is provided by either:
      1. a resistor divider between the supplies.
      2. a pull-up resistor to RLDOUT.

    Using a pull-up resistor to RLDOUT should still help improve CMR.

    Hope this helps!

  • 0 in reply to Ryan Andrews
    TI__Expert 3560 points

    Hello Ryan,

    Thanks for your input.

    My query is related to Figure 62 of ADS1292R datasheet. In that figure there is a RESET pulse on after tPOR.

    I wanted to know, is it necessary to generate this pulse after power up for proper operation of ADC? If yes, then a dedicated controller pin will be required to generate the pulse.

    OR

    tPOR is the minimum time period after which device can be RESET? and is it OK to pull this pin high, if RESET functionality is not to be used?

    Also, regarding RLD, do you have a reference schematic which shows an implementation of pull up to RLDOUT?

    How to calculate value of pull-up resistor?

    In this case, where to connect RLDIN/RLDREF? 

    Thanks & regards,

    Mahendra Patel

  • 0 in reply to Mahendra Patel1
    TI__Guru 66466 points

    Hi Mahendra,

    1. The extra reset pulse after tPOR is not absolutely necessary, but highly recommended. This is to ensure that the device is in a known good state after power-up. If you wish to hold the /RESET pin high, you can send a RESET SPI command instead (0x06).
    2. For example:

    Keep in mind that the value chosen for the RLD pull-up resistor will form a high-pass filter with the DC blocking cap in series with each electrode. 10M to 100M ohms should be fine.

    3.  RLDIN/RLDREF is not needed if RLDREF_INT = 1. This will set the common-mode of the RLD amplifier to mid-supply.

    Best Regards,