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AMC0311S-Q1: AMC0311S-Q1

Sumeet Patil
Intellectual 270 points
Part Number: AMC0311S-Q1
Other Parts Discussed in Thread: AMC3330, ISO122, ISO124, ISO121, ISO224, AMC0380D, INA851, SN6501, SN6507

Tool/software:

Hi Ti Amplifiers team

I am facing a ground loop issue which causes 50Hz ground loop in my amplifier chain. Can using this amplifier 

AMC0311S-Q1

along with differential amplifer break the ground loop.

Do you have similar architecture part that gives out 5V or 10V instead of 2V? Please let me know, I look forward to hearing from you soon.

  • 0
    TI__Expert 3131 points

    Hello Patil, using an isolation amplifier effectively breaks the grounding loop. In this case it acts as a Functional Isolation. The AMC0311S-Q1 is a good universal building block to achieve this function. The drawback is that you also need to create an isolated power supply for that (since you can't share grounds as you have ground loop problem).

    Another part you could consider is AMC3330 that comes with a differential output and integrated DC/DC converter.

    We do have devices with output of 5V or 10V - ISO121, ISO122, ISO124. Please note that these are old devices (still heavily used) and cost premium.

    Kind regards, 

    Jiri 

  • 0 in reply to Jiri Panacek85
    Intellectual 270 points

    Hello Jiri,

    Thanks for reverting back, My actual application is very sensitive analog chain with high impedance sensors. I want to break down the ground loop in my existing sequence. My max output will be sine wave that is +/- 15V, ideally i would like to have a single ended output from isolation amplifier. As my input signal to isolation amplifier will be single ended input centered at 0V with some bias with peaks of +/-15V. I hope you understood my application. What is the level of isolation ISO series provide.

    What is difference between ISO121, ISO122, ISO124 and ISO224 amplifiers with respective to AMC3330 and AMC380D

  • 0 in reply to Sumeet Patil
    Intellectual 270 points

    Hi Jiri,

    Could you please answer my questions raised in earlier reply of mine.

  • 0 in reply to Sumeet Patil
    TI__Expert 3131 points

    Hello Sumeet, 

    You mention a very sensitive analog signal chain - have you consider using a delta-sigma modulator instead? Modulators are a type of devices I would recommend for the best signal fidelity. The reason for that is simple - an isolated amplifier is a delta-sigma modulator and filter in the same package. In our AMCxxxx portfolio, we cross the isolation barrier with a digital signal using a capacitive isolation. This means, there is practically A/D and D/A conversion in one package. Every conversion naturally adds noise and error to the signal.Frequently, applications with isolated amplifiers use another A/D converter to process the signal. This means -> A/D -> D/A -> A/D conversion. The problem with modulators is that they need dedicated delta-sigma filter module (e.g. SDFM in C2000 MCU).

    Now back to your questions:

     The AMC3330 and AMC0380D are modern devices. Especially the AMC0380D is a fresh release this year (generally the portfolio of isolated devices AMC0xxx).

    The ISO12x series dates back to Burr Brown development. For example, ISO122 is from year 1993. They are ancient devices both in terms of performance and technology. This family does not use a delta sigma modulator for ADC conversion. However, certain conservative markets still use these parts.

    ISO224 is already a newer part from 2018. It uses a modern approach with delta sigma conversion. The input range is +/-12V

    AMC0380D is a high voltage sensing device. You don't need that one.

    Looking at our portfolio, you can't solve your design challenge with only isolated amplifier. You need to pair it with a difference amplifier on the output (I would use OPA911) that boosts the voltage from the isolated amplifier.

    Additionally, you need an attenuation at the input. Your sensors are high impedance. For this reason, I suggest using an instrumentation amplifier  that is capable of gain smaller than 1. INA851 can go down to 0.2.

    PS: There is also a method to make it completely analog. Have a look at SIM984 Isolation Amplifier from Stanford Research. The operation and service manual is available online. It contains schematic. It uses a linear optocoupler for the isolation. We do not manufacture these. However, if you decided to follow this path, please have a look on SN6501, SN6505 or SN6507 push pull transformer drivers for generating the isolated voltage.

    Kind regards, Jiri

  • 0 in reply to Jiri Panacek85
    Intellectual 270 points

    Hi Jiri,

    Thanks for your answer. I can not use SIM984 approach as my device needs to be very compact.

    Based on your reply, it seems that sigma delta modulation is will ensure best signal fidelity. So do AMC series: AMC3330 and AMC0380D uses it? Or does it follow traditional A/D and D/A conversion approach using capacitive approach?

    Is ISO224 using sigma delta modulation? You mentioned it earlier, I just want to confirm it?

  • 0 in reply to Sumeet Patil
    TI__Expert 3131 points

    Hi Sumeet, 

    all the parts that I recommended (AMC and the ISO224) use the delta sigma modulation. But in fact, this is still an A/D and D/A conversion. 

    Delta-sigma modulator is a form of an AD converter. The delta-sigma filter is a form of a DA converter.

    Best regards, Jiri

  • 0 in reply to Jiri Panacek85
    Intellectual 270 points

    Hi Jiri,

    Thank you for the information. I have a follow up question which is out of AMC and ISO 224 devices which  one's AD and DA conversion will introduce less error? Can that error introduction be quantifiable? I can put that error margin in my calibration setup to account for it.

    In one of your comments, you mentioned this In our AMCxxxx portfolio, we cross the isolation barrier with a digital signal using a capacitive isolation, I am little confused here, do ISO224 also uses capacitive isolation? What is the difference between the AMC and ISO224 devices?

  • 0 in reply to Sumeet Patil
    TI__Expert 3131 points

    The ISO224 also uses capacitive isolation. I do not know much about this product but I believe it was designed as an update to the old ISO12* family .

    It also uses the delta sigma conversion. Speaking for errors, I will point you to respective device datasheets and online comparison tool. The overall error is a combination of multiple sources (THD, SNR, offset error, gain error, drift). It is difficult for me to quantify it. 

  • 0 in reply to Jiri Panacek85
    Intellectual 270 points

    Hi Jiri,

    Thanks for replying to my question, one question that came to my mind, is the frequency of AC signal that will be fed to the amplifier. The frequency of the AC signal of my interest is 1Hz to 100 kHz, can this be passed reliably through ISO224 or AMC3330? Please let me know.

  • 0 in reply to Sumeet Patil
    TI__Expert 3131 points

    Hi Sumeet, the AMC3330 has the typical bandwidth 375kHz (to the -3dB point).

    Refer to Figure 5-9 and 5-10 of the device datasheet.

    At 100kHz the phase shift is already -50 deg. This is something you need to consider. 

    The ISO224 has a lower bandwidth of 185/275kHz based on the version. At 100kHz, the phase is already lagging 90 degrees (Figure 19, Figure 20 of the device datasheet).

    As the rule of thumb, we suggest always the bandwidth being at least ten times higher than the signal of interest. However, we do not have any 1MHz device.  

    Best regards, Jiri

  • 0 in reply to Jiri Panacek85
    Intellectual 270 points

    Hello Jiri,

    I noticed that AMC3330 has better noise performance over ISO224, however my concern is with the resistive divider needed in AMC3330, I have +/-15V 30 Vpeak to peak signal, I would need that to be brought into VFSR region of AMC3330. Can you help me with that? I slight confused with respect to Rsns value? Can you help me on that? Secondly, I have an isolated power supply power my entire amplifier chain prior to AMC3330, is it okay to connect its ground to HGND of AMC3330 or should I leave it open

  • 0 in reply to Sumeet Patil
    Intellectual 270 points

    Hi Jiri,

    Can you please revert to my earlier question

  • 0 in reply to Sumeet Patil
    Intellectual 270 points

    Hi Jiri,

    Can you please answer my earlier question.

  • 0 in reply to Sumeet Patil
    TI__Guru 55652 points

    Hi Sumeet, 

    Please see the cookbook circuits in this document for assistance with resistor divider design: https://www.ti.com/lit/eb/slyy234/slyy234.pdf

    Yes, your input signal to the AMC3330 and analog signals through prior components would all need to be referred to the same net.