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ADS1299: PWDN effect on the I/O - Multiple Device Configuration

TISL
Expert 4630 points
Part Number: ADS1299

Dear e2e Support,

My customer is using up to 4x ADS1299 per board.

Depending different configurations, 1, 2 or 3x ADS1299 can be put in shutdown.

In this multiple device configuration and when PWDN is active:

- what are the digital I/O status pins? are they disconnected?

- can we tie together the signal RESET, START, SPI, and ADS_CLK, coming from the different ADS1299?

- what is the status of the output BIASINV?

- what is the quiescent current of our chip in this case of PWDN active and when the clocks are still running (CLK/MOSI, etc...)?

Regards,

  • 0
    TI__Guru 66256 points

    Hello,

    I assume that the analog and digital power supplies of the powered-down ADS1299 devices remain present? If so, then there should be no issue with sharing the digital I/O pins between powered-down and active ADS1299 devices. The digital inputs will be ignored during power-down and will not damage the devices as long as the supplies are present. The digital outputs will be high-impedance unless powered-on and /CS is active.

    Yes, /RESET, START, SPI signals, and CLK can be shared. Please refer to the Daisy-Chain and Cascaded configurations described in section 10.1.4. It is recommended to use the same CLK source for all devices. This can be an external crystal oscillator to all CLK pins, or you may take the internal CLK from one device and output it on the CLK pin to be shared with the remaining devices.

    BIASINV is the inverting input of the BIAS amplifier. During normal operation, with all ADS1299 devices powered-on, it is recommended to power down all but one BIAS amplifier. You may still connect all BIASINV pins together in order to increase the number of electrodes used for common-mode derivation.

    The interface will be completely disabled during power-down. If you're using the internal oscillator, it will be shut down until power-down is removed. The power dissipation is specified in the Electrical Characteristics section of the data sheet.

    Best regards,

  • 0 in reply to Ryan Andrews
    Prodigy 20 points

    Dear Ryan,

    Thanks for your reply. I come back for the BIAS amplifier.

    In fact, I already connect all bias inv pins together in order to increase the electrodes number for CM derivation. That's why I come back to you, because I can use 1x ADS but also 4x ADS, or 2x ADS... So if I well understand you, all switches at intput and output on figure 38 are open when PWDN is active, isn't it ? (beacause I don't want to perturb my RLD when only 1 ore more ADS are used...)

    Best Regards,