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AMC1301: how many bits of resolution are the output of AMC1301.

ych_chn
Intellectual 345 points
Part Number: AMC1301
Other Parts Discussed in Thread: TIDA-01541

Tool/software:

Hello expert,

I have a question about the White Paper "SBAA359A Comparing Isolated Amplifiers and Isolated Modulators".
According to the documentation, Isolated Modulators have an advantage over Isolated Amplifiers due to their flexibility. Isolated Modulators with a delay of 2.4us have a resolution of only 10.02 bits.

However, in the document TI Designs "TIDA-01541 High-Bandwidth Phase Current and DC-Link Voltage Sensing Reference Design for Three-Phase. The AMC1301 used in Inverters, with a latency of only 2.5us, seems to achieve much higher bandwidth. I would like to ask whether Isolated Amplifiers sacrifice resolution with such low latency, and how many bits of resolution are the output of AMC1301.

thank you

  • 0
    TI__Expert 8455 points

    Hello,

    Since the AMC1301 is an amplifier, it has analog output instead of digital. Therefore, the resolution would not be described in bits but in volts. The AMC1301 outputs +/-2.05V on pins OUTP and OUTN. The AMC1306 is a modulator with digital output which is why the output is specified in bits. 

    Generally, isolated modulators will be more accurate than isolated amplifiers. When intending to work with digital output, using a modulator reduces the number of stages necessary in a system. 

    In the example you've shown, the modulator at OSR = 32, the BW is 312.5kHz while the amplifier lists a BW of 210kHz. So, the modulator shows higher bandwidth still. 

    Please let me know if there are more questions, thank you. 

  • 0 in reply to Eva Mason
    Intellectual 345 points

    Thanks to the experts :
    Although the isolation amplifier is an analog output, it has also been digitally isolated, and its resolution and delay should have a limit. The parameter in the delay manual is 2.5us, what is the upper limit of its resolution?

    The modulator shows higher bandwidth, but with a delay of 2.5us, the resolution is only 10 bits. If the isolation amplifier has no upper resolution limit, then the isolation amplifier is better than the modulator.
    Thank you!

  • 0 in reply to ych_chn
    TI__Expert 8455 points

    That is not a parameter we specify in the datasheet. However, the table you screenshotted in the original question demonstrates that modulators will have higher accuracy and performance. 

    What is your application? 

  • 0 in reply to Eva Mason
    Intellectual 345 points

    For my application and for high bandwidth motor control, I use a modulator to achieve a 12-bit resolution that generates a 5us delay, which limits the use of fast current loops, but only a 2.5us delay if using an isolated op amp.

  • 0 in reply to ych_chn
    TI__Expert 8455 points

    If you consider the relationship between SNR and ENOB for the AMC1301:

    • ENOB = (SNR-1.76)/6.02
    • AMC1301's ENOB Estimate = (71-1.76)/6.02 = ~11.5 bits

    However, this does not include additional error from an ADC. So, if you would still need to convert the output to single-ended, the resolution of the modulator could be higher if you use a higher OSR such as 256.