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ADS131M04: ADS131M04

Saisivarajagopal KS
Prodigy 50 points
Part Number: ADS131M04


Hi All,

For our energy meter we have selected this ADS131M04 for metrology measurement(For Current and Voltage measurement). I have few queries on the specification

1. Does this Part has inbuilt Zero crossing detection for AC lines? It is not mentioned anywhere in datasheet. and in reference design also i couldn't see any external IC for Zero crossing?

whether it should be taken care  through software in external MCU connecting to it?

2. Does this part support Hall effect sensor for current measurement?

3. I have a requirement of ENOB 16bit for 4kSPS and 32kSPS? does this Part support ENOB of 16 bit for above datarate?

4. I need to know what problems will happen i use two ADS131M04 for polyphase meter by sharing the SPI channel? does this affect the datarate or delay in processing?

  • +1
    TI__Mastermind 18900 points

    Hello Saisivarajagopal,

    1. Does this Part has inbuilt Zero crossing detection for AC lines? It is not mentioned anywhere in datasheet. and in reference design also i couldn't see any external IC for Zero crossing?

    No, the ADS131M04 does not have zero crossing detection so it needs to be handled through software in the external MCU

     

    1. Does this part support Hall effect sensor for current measurement?

    At a high level, yes the device can support a hall effect for current measurement. At the end of the day, the inputs to the PGA are high impedance and its looking at AINxP and AINxN as differential inputs that measure voltage. 

     

    1. I have a requirement of ENOB 16bit for 4kSPS and 32kSPS? does this Part support ENOB of 16 bit for above datarate?

    According to noise measurement information section, we’re given the following equation and table.

    I’ve highlighted the effective resolution calculation that fit your criteria

     

    1. I need to know what problems will happen i use two ADS131M04 for polyphase meter by sharing the SPI channel? does this affect the datarate or delay in processing?

    No inherent problems in using multiple ADS131M04s, please review section 9.1.4 titled Multiple Device Configuration, in the datasheet.

    The most typical issue that is overlooked is not clocking out the data fast enough before the next nDRDY signal (i.e. faster than your data rate). This then translated to stricter SCLK requirements and good SCLK conditioning.

    Best,

    -Cole

  • 0 in reply to Cole Macias
    Prodigy 50 points

    Thank you Cole Macias, Also i want to know -3db bandwidth supported by this devices.  I need a -3db bandwidth of 12Khz to 16KKhz

    Sorry If my question is too dumb, I couldn't get the information explicitly on datasheet. 

    Could you please help me on that.

  • 0 in reply to Saisivarajagopal KS
    TI__Mastermind 18900 points

    Hello Saisivarajagopal,

    No worries, let's see if I can answer your question.

    Short Answer:

    In general, the PGA has been designed to have a flat frequency response at every gain setting so only the sampling rate, and therefore the digital filter response, should be the factor whether you can measure 12kHz to 16kHz. Take a look at Figure 8-1, -2, -3, and -4 too see the roll off. 

    Long answer:

    For a longer explanation, I see the term "-3dB bandwidth", I assume you mean "bandwidth that does not attenuate the signal below -3dB of its intended gain". Remember, the roll off from 0dB to -3dB is not instantaneous, attenuation occurs well before the -3dB point. Some would argue that even -1dB or even -0.1dB is not usable bandwidth, even though text books have taught "up to -3dB, or half the power of the signal is good enough to be called usable bandwidth".

    With all this said, the PGA has been designed for a flat response so none of the -3dB or pre -3dB roll off affects the signal that is measured. That doesn't mean that the PGA doesn't include error (i.e. the PGA includes error), this can be found in the datasheet section for gain and offset (which are DC error that affects the whole bandwidth).

    So what's left is the sample rate. You can't measure 16kHz if your sample rate 4kSPS as the digital filter stage will attenuate that signal, according to the Nyquist theorem and basic delta-sigma design. This is why you should go look at the f_in/f_data digital filter plots see the roll depending on the type of filter you decide to use in your system.

    Hope that helps     

    Best,

    -Cole

    Edit: added digital filter info