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ADS1194: ADS1194 AND ADS1198 PIN CONNECTION

Part Number: ADS1194
Other Parts Discussed in Thread: ADS1198

Hello.

I want to use ADS1198 and ADS1194 as 12ch input.

I don't use WCT, GCT, RLD, PACE, GPIO.

(Input Conditions)

[Power Setting: AVDD = +1.5(V), AVSS = -1.5(V), DVDD = +3.3(V), DGND = 0(V)]

[External References: VREFN = AVSS, VREF = VREFP - VREFN = +2.5(V)]

[Input-Signal: AINN = 0(V)( =AnalogGND), VIN = AINP-AINN = AINP]

I have the following questions.

<Question>

1. Are IN8 ~ IN5 (No. 1 ~ 8) of ADS1194 connected to AVDD (not OPEN)?

2. Are NC(No. 27, No. 29) OPEN?

3. Are GPIO 1 to 4 connected to DGND?

4. Is RLDREF(No. 60) OPEN?

Connect a CR (1500pF, 1MΩ) filter between RLDINV (No. 61) and RLDOUT (No. 63) for only one IC.

Another IC opens RLDOUT (No.63), Should I connect RLDINV (No. 61) of both ICs?

I see so it when I watch P.60 fig.52.

※See attachment CONNECTION.pdf.

5. Even if WCT (No.64) is not used, is 100pF connected to No.64?

※See attachment CONNECTION.pdf.

6. Is the power supply connection (AVDD, AVSS, DVDD, DGND) and Input-Signal as shown in the attached figure?

※See attachment CONNECTION.pdf.CONNECTION.pdf

  • Hello,

    Thank you for your post. We are happy to review your pin connections below:

    1. Yes - unused inputs should be pulled-up to AVDD.
    2. Yes - NC means "no connection"
    3. Yes - short unused GPIOs to DGND.
    4. If internal RLDREF is used, this pin is not connected internally and may be left floating. RLDIN can be left floating also if unused. RLDINV may be shared among other ADS119x devices, but this is only necessary if more electrodes are used to derive the RLD common-mode signal. Adding more electrodes will alter the gain of the RLD loop. See our ADS129x BIOFAQ page for more details. The powered-down RLD amplifiers may leave RLDOUT, RLDREF, and RLDIN pins floating.
    5. WCT bypass cap is not necessary if WCT output is not used. Power-down unused WCT amplifiers internally to save power.
    6. Analog and digital ground split is ok, but remember to place the 0-ohm short as close to the ADC as possible, perhaps directly below on bottom layer. Input amplifier stage should not be necessary with internal PGA in the ADS1198.

    Best regards,

  • Thank you very much Ryan Andrews.


    ・Question 1 to 3

    →I understood.

    ・Question 4

    >RLDIN can be left floating also if unused.

    →Since RLD is not use, I set RLDIN to NC, right?
    ・Question 5

    >WCT bypass cap is not necessary if WCT output is not used.

    →Since WCT is not use, I set WCT to NC, right?
    ・Question 6
    >Analog and digital ground split is ok, but remember to place the 0-ohm short as close to the ADC as possible, perhaps directly below on bottom layer.

    →Is it better to eliminate the digital-ground and connect only to the analog-ground as shown in the figure?
    Also, should the decoupling capacitor be connected as shown in the figure?

    ※See attachment CONNECTION-2.pdf.CONNECTION-2.pdf

    >Input amplifier stage should not be necessary with internal PGA in the ADS1198.

    →I placed AMP in the previous stage because the amplification is not enough.

  • Hello,

    Yes - RLDIN and WCT may be left floating (NC) if unused.

    Decoupling caps look good as shown in the diagram. Analog supplies should be decoupled to the analog ground and digital supplies should be decoupled to the digital ground. However, all of your DC/DC converters will introduce some switching noise. It might be better to reference these switching converters to "DGND" and only allow the amplifier + ADC (i.e. the analog side of the PCB) to reference the "AGND." Power and digital sections of mixed signal PCB should be kept separate from the analog section, if possible. 

    Removing the ground split and using a solid ground is also ok. When designing the PCB layout, it can be helpful to place and route components with the split. Then, remove the ground split as the final design step. The form-factor of the PCB does not always allow for components to be spaced properly, so a ground split is sometimes a safer option.

    Best regards,

  • Thank you Ryan Andrews.

    >Yes - RLDIN and WCT may be left floating (NC) if unused.

    →I understood.

    >Decoupling caps look good as shown in the diagram. Analog supplies should be decoupled to the analog ground and digital supplies should be

    >decoupled to the digital ground. However, all of your DC/DC converters will introduce some switching noise. It might be better to reference these

    >switching converters to "DGND" and only allow the amplifier + ADC (i.e. the analog side of the PCB) to reference the "AGND.

    >" Power and digital sections of mixed signal PCB should be kept separate from the analog section, if possible.

    →I understood.

    I separate the power supply and digital section from the analog section.

    >Removing the ground split and using a solid ground is also ok.

    →Excuse me, please tell me.What is "solid ground"?

    >When designing the PCB layout, it can be helpful to place and route components with the split.

    >Then, remove the ground split as the final design step. The form-factor of the PCB does not always allow for components to be spaced

    >properly, so a ground split is sometimes a safer option.

    The ADC DGND connection will be split with the AGND with a 0Ω resistor as shown in the figure. Is that okay?

    ※See attachment CONNECTION-3.pdf.CONNECTION-3.pdf

  • Hello,

    Solid ground simply means "continuous" or "non-split" ground plane.

    I think the split with a 0-ohm resistor directly next to or underneath the ADC is ok. 

    Regards,