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ADS131M03-Q1: Guidance for CT interfacing with ADS131M03--Q1

Neet
Intellectual 612 points
Part Number: ADS131M03-Q1
Other Parts Discussed in Thread: ADS131M03, INA236

Dear Community,

We are currently in the process of developing an ultra-low-cost current monitor specifically designed for Micro and Small Industry owners in India. Our goal is to ensure that the device remains within a price range of 12 USD.

After careful consideration, we have chosen the ADS131M03-Q1 as our primary ADC for interfacing with the MCU to analyze current consumption signals.

To measure the current, we have opted for a high-precision Current Transformer (CT) with a burden resistor of 33Ω and a DCR (DC Resistance) of 85Ω. The CT provides an output of 0.4V at 30A and 0.8V at 60A, while maintaining 0.2% accuracy within the 10A to 60A measuring range, considering the specified Burden Resistance. Following are the Current Transformer Specifications.

At this point, we would greatly appreciate guidance from the community on the following matters:

  1. With the ADS131M03 operating at a gain of 1, 2, and 4, and featuring a 330-kΩ input impedance, do we need an additional buffer between the CT and the ADS131M03?

  2. We would also appreciate any recommended guidance for protection circuitry in this particular setup assuming cost-optimized implementation.

We are open to any and all forms of support and guidance that you can provide.

Thank you for your assistance.

Regards.

  • 0
    TI__Mastermind 45955 points

    Hi Shreeneet,

    I will look into the details and get back to you soon, thanks.

    Regards,

    Dale

  • +1 in reply to Dale Li
    TI__Mastermind 45955 points

    Hi Shreeneet,

    Thank you for your patience, please see my response below:

    • The impedance of CT is not high comparing with the equivalent input impedance of M03 ADC, and also CT already offers isolation, so an additional buffer is usually not required.
    •  To protect the input of ADS131M03, please see the app note as a reference: Circuit for protecting ADS131M0x ADC from electrical overstress

    Best regards,

    Dale

  • 0 in reply to Dale Li
    Intellectual 612 points

    Hello Dale,

    We came across the INA236, which appears to be a promising solution for our current and voltage monitoring needs. It offers the ability to measure both current and voltage, as well as provide power readings, all through the I2C interface.

    In comparison to using multiple ADS131M03 devices for separate current and voltage measurements, the INA236 seems to be a more affordable and convenient option. However, we seek guidance in making an informed decision.

    Our specific query pertains to using a separate current transformer (CT) as the input source for current measurement, along with a separate potential transformer (PT) and a suitable resistor divider network for voltage measurement. We intend to employ the INA236 (or similar built in ADC power monitor) in this configuration for monitoring current and voltage across a 3-phase motor, with current range of 5A to 90A & voltage range of 230VAC to 480VAC. The objective of using transformers is to isolate the measurement system from the high-current sides.

    We would greatly appreciate your expertise and advice on the following points:

    1. Is it feasible to utilize the CT as the input source for current measurement and the PT with a suitable resistor divider network for voltage measurement in conjunction with the INA236? Pinout of INA236 does not seem to support separate Voltage pins. 
    2. What are the key considerations and challenges we should be aware of when implementing this configuration?
    3. Are there any specific guidelines or best practices to ensure accurate and reliable current and voltage measurements using the INA236 in this setup?

    We eagerly await your insights and recommendations based on your experience. Additionally, if there are any specific details or clarifications required to better address our query, please let us know.

    Thank you in advance for your valuable assistance.

    Warm regards

  • 0 in reply to Neet
    TI__Mastermind 45955 points

    Hi Shreeneet,

    I'm not an expert for INA236, this is a forum for data converters, you can ask the questions about INA236 on the Amplifier Forum. For ADS131M0x ADC, CT is commonly used to measure current, you can use PT or just use resistor divide network to measure voltage. We have released many reference designs for current and voltage measurement based on ADS131M0x ADC, below is one of them:

    Cost-Effective, 3-Phase CT Electricity Meter Reference Design Using Standalone ADC

    Please let me know if you are still interested in the standalone ADC solution and have any questions about ADS131M0x ADCs.

    Thanks&regards,

    Dale