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MSP430I2020: Hardware design Guideline for inbuilt 24bit ADC

Part Number: MSP430I2020

Hello,

I have to consider MSP430I2020 controller for ongoing project. it has built in 24 bit ADC, this is the reason that why i'm using this controller. actually my project is based on weight scaling. so i want to interface my load cell 300kg(capacity) with this controller. 

Load cell gives 2mv at full load, excitation voltage is 5V, so maximum output voltage of load cell at full load is 10mV, i use internal reference voltage for ADC that is max 1.7V.

I have to connect amplifier between load cell and controller that can amplify load cell output from 10mv to 1.2v so ADC pin can easily sense this voltage.

For the confirmation, is it ok??

1. 2^24 = 16777216 step size

2. 1.2/16777216 = 0.000000072 V per step size.

Question: what is the minimum sensitivity of ADC. is ADC can sense 0.000000072 V?

Any external RC anti-aliasing filter circuit is required for ADC, if possible then please share a reference schematic for ADC filter circuit.

Thank you

  • Hi Shashikant,

    Regarding your question of confirmation for your application, the process of amplifying the small signal coming from the load cell seems like a solid solution. FYI there is an on-board programmable gain amplifier that might meet your requirements in case you haven't looked into that option.

    Now regarding your question on sensitivity; the 24 bit ADC has a resolution of (Vref+ - Vref-) / 2^24. This is the resolution, and in an ideal world would also be your sensitivity; but when you take into account signal to noise ratios and harmonic distortions you end up with an ADC that does not have ideal sensitivity. This is where the concept of Effective Number of Bits (ENOB) comes into play because it approximates an estimation of what the actual resolution would be given certain noise parameters. Here is a technical paper which explores ENOB and how to approximate it ( cdn.rohde-schwarz.com/.../ENOB_Technical_Paper_1ER03_1e.pdf )

    The ADC parameters needed to calculate values such as ENOB can be found in Table 5-22 of the device's datasheet ( www.ti.com/.../msp430i2020.pdf ).

    Here is a presentation which shows some examples of noise reduction and anti-aliasing filters to use in front of an ADC ( www.ti.com/.../slap123.pdf )

    Best regards,

    Matt
  • Hi Shashikant,

    I noticed that you selected that the previous post did not help you reach a resolution. Please provide any further detail that may help us resolve this.

    Regards,
    Matt
  • Hi Shashikant,

    Thank you for providing a snippet of your schematic and a datasheet of the load cell you are using. I've provided information on how you can estimate the sensitivity you can expect from the 24-bit ADC. The best way to know the sensitivity for your specific design is to analyze test data captured from the load cell itself. Is there any other open issue regarding this thread?

    Best regards,

    Matt

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