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ADS1299: ADS1299 Cascaded Configuration: SRB Routing and Bias Pin Connections Clarification

Theeban Raj
Prodigy 10 points
Part Number: ADS1299

Tool/software:

Hi TI Support Team,

We’re using three ADS1299 chips (24 channels total) in cascaded mode. 21 channels are for EEG (referential montage), and 3 are for true differential EMG.

We’d like your help confirming the correct setup for shared reference and bias configurations.

1. SRB2 vs SRB1 Internal Routing
Does setting CHnSET[3]=1 connect SRB2 to INxP, and MISC1[5]=1 connect SRB1 to all INxN? Based on this, is it valid to connect EEG electrodes to INxN, use SRB2 as a common reference, and invert the data in software (i.e., signal = INxN − SRB2)?

2. BIASOUT and BIASIN Connection Between Devices
Is it correct to use BIASOUT from Device #1 as the active bias driver, connect BIASIN of all three devices to it, and leave BIASOUT of Devices #2 and #3 unconnected? Should these unused BIASOUT pins be left floating or tied to AVSS?

3. BIASINV Pin Usage
If we do not use the BIASINV pin, should it be left floating or tied to AVSS?

Thanks in advance for your support.

  • 0
    TI__Expert 6670 points

    Hi Team,

    Thank you for your support.

    Kind regards,

    Marvin

  • 0
    TI__Guru 66446 points

    Hello Theeban,

    1. Yes. SRB1 connects to all INxN. SRB2 connects to each channel's INxP input and is selectable on a channel-by-channel basis. How you connect your electrodes to the positive or negative side of the channels is up to you.

    2. Please refer to section 9.3.2.4.5.1 for details about connecting the BIAS amplifiers from multiple ADS1299 devices. BIASOUT can be left floating and the amplifier can be powered down if unused.

    3. Please refer to section 10.1.1 for treatment of unused analog and digital pins.

    Regards,

    Ryan