ADS1299: Resistance value measurement method between IN7P and IN7N

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Replies: 11

Views: 189

Part Number: ADS1299

Dear TI Team

Our customer is trying to measure the resistance value between IN7P and IN7N using the Lead off Detection function of ADS1299 with the following settings.

1. A resistor is inserted between the IN7P pin and IN7N pin to make it short-circuited.
2. Set the register as follows

  • ILEAD_OFF: 24uA
  • CH7SET: 0x60
  • (Set with PD7: Normal Operation, GAIN7: 24, SRB2: Open, MUX7: Normal)
  • LOFF_SENSP: IN7P only Set with Enable (0x40)
  • LOFF_SENSN: IN7N only Set with Enable (0x40)
  • MISC1: SRB1 set with Switches open

Can you give me some advice as to whether it can work with the above settings?

Best Regards,

Y.Ottey

11 Replies

  • Hello Ottey,

    Is the customer running into any issues when they try to measure the impedance?

    Please share the input channel network configuration and the complete register settings.

    Regards

    Praveen

    TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning your designs.

  • In reply to Praveen Aroul:

    Hi Praveen

    Thank you for your reply.

    When our customer measured the impedance in the settings of yesterday's post, the connected resistance value cannot be measured.
    (It is not output with a certain value.)

    I would like to ask the customer about the above, but I would like to ask you an additional question.

    1.Does the input part (IN7P, IN7N) need to have the configuration shown in the figure below?
    (I think that it is not possible to measure by just putting a resistor between IN7P and IN7N like yesterday's post.)

    2.Is there a register other than LOFF_SENSP and LOFF_SENSN that should be set when operating in the lead off detection state?
    (What registers should I check other than the register settings posted yesterday?)

    Regards,

    Y.Ottey

  • In reply to Y.Ottey:

    Dear Praveen

    I would like to know the content of the additional question in order to get information from our customers.
    I would be grateful if you could reply as soon as possible.

    Regards,

    Y.Ottey

  • In reply to Y.Ottey:

    Hello Ottey,

    To help us debug further into the issue,  please share the customer's input channel network configuration and the complete register settings that they are programming the device with. Please share the waveforms.

    Have they tried to reduce the lead off current magnitude or the channel gain? Are they using the TI ADS1299 EVM to make these measurements or their own custom built board?

    To answer your questions,

    1. Yes, it is possible and it depends on the impedance that they are trying to measure.

    2. Other than the register settings mentioned in the previous post, are the remaining registers programmed to 0?

    Regards

    Praveen

    TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning your designs.

  • In reply to Praveen Aroul:

    Hi Praveen

    Thank you for your reply.

    The input side configuration that our customers are implementing is as follows.
    I checked R1 with the following values, but I cannot measure the resistance value that matches R1. (If you need to check the detailed output data, we will send it offline.)
    ・ R1 = 0Ω (short state)
    ・ R1 = 1kΩ
    ・ R1 = 100kΩ

    The circuit is different from the data sheet Figure.35, but could you advise if there are any factors in the following circuit configuration?
    (We are currently checking the power supply configuration and register settings other than AVDD.)

    Regards,

    Y.Ottey

  • In reply to Y.Ottey:

    Hi Ottey,

    I think there is a typo in your diagram where it shows R1 is connected across 2 different channels. You should be able to measure the impedance R1 in the diagram you are showing in this configuration if R1 is connected to IN7P and IN7N in your initial post. Please be aware that the DC LEADOFF current accuracy specification in the Electrical characteristic table when calculating the impedance. Please refer to Figure 17 in the datasheet for the Lead-Off current source accuracy plot for the 24nA current setting. To account for the LEADOFF current accuracy, the RLD amplifier needs to be activated, and the output needs to be at the proper biasing.

    Please provide the data offline if you have some.

    Thanks.

    -TC

  • In reply to TCT:

    Dear TC

    Thank you for your reply.

    I'm sorry, but there is a mistake in the schematic I sent you.
    I want to send you data offline, but I want you to exchange it in a private message.

    regards,

    Y.Ottey

  • In reply to Y.Ottey:

    Hi Ottey,

    Please send any data to the ADS129x AFEs support at ads129x-support@list.ti.com.

    -TC

  • In reply to TCT:

    Hi TC

    Thank you for your reply.

    I sent the output data and circuit to the email address you wrote.
    Have you received it?

    Regards,
    Y.Ottey

  • In reply to Y.Ottey:

    Hello Ottey,

    We have received your email.

    TC is on vacation and will be back on Jan 4.

    He will respond to your queries when he returns.

    Thanks for your patience and understanding.

    Regards

    Praveen

    TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning your designs.