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ISOM8110: Maximum Data Frequency this Opto-Emulator can transmit

Neet
Intellectual 532 points
Part Number: ISOM8110
Other Parts Discussed in Thread: ISOM8710, ISOM8711

Tool/software:

Hello E2E Community,

We have a pulse output (88kHz) sensor with 3.3V in our system, and plan to isolate the sensor from the MCU Board by using ISOM8110 Optoemulator.

Kindly suggest if we this device is advisable for the given frequency range.

  • 0
    Guru 267960 points

    Normal phototransistor optocouplers have an analog bandwith of about 80 kHz, but would not be able to transmit digital signals with more than about 10 kbps.

    The ISOM8110 is designed to replace them. It is much faster (680 kHz analog); for digital signals, we can estimate its limit at about 85 kbps = 42 kHz. (I do not know what exactly your "88 kHz" value measures.)

    I would stronly suggest to use a digital isolator like the ISOM8710.

  • 0
    TI__Mastermind 18335 points

    Hello Neet, 

    Thank you for reaching out. 88kHz may be too fast for the ISOM8110 and ISOM8710 is preferred for higher speeds.  ISOM8110 is an analog output opto-emulator and in saturation mode (when IF>Ic_max) the data rate is realistically ~50kHz. Data rates faster than 50kHz need to be tested with your system to see if they are acceptable.  

    Best,
    Andrew

  • 0 in reply to Clemens Ladisch
    Intellectual 532 points
    Clemens Ladisch said:
    we can estimate its limit at about 85 kbps

    Hello ,

    These are current pulses converted into voltage pulses that shall be fed to the MCU & we plan to use an isolation barrier.

    We are also evaluating use of f/2 or f/4 D Flip Flop to convert these input pulses into 22kHz waves or 44kHz waves which shall have carry about 3000 pulses as signal at said frequencies.

    So given this use case, would you recommend using the lower cost ISOM8110?

    Also, we have ISOM8711 in stock - would you recommend using it instead for this use case?

  • 0 in reply to Andrew Jackiw
    Intellectual 532 points
    Andrew Jackiw said:
    ISOM8110 is an analog output opto-emulator

    Hello ,

    Thank you for your response. Can you help elaborate more on Analog output Opto-emulator?

    Can we interface analog voltage signals at 10Hz frequency through ISOM8110?

    Kindly guide

  • 0 in reply to Neet
    TI__Mastermind 18335 points

    Hello Neet, 

    The "analog output" indicates that there is transistor that will mirror the input current on the ISOM8110 and not CMOS buffer on the output. The output transistor of ISOM8110 can be operated in the transistor's saturation region to force a digital square-wave output. A transistor is in saturation mode when the Collector current is limited below the diode forward current. This can be achieved with an input resistor of 120-ohms and a pull-up resistor on the collector of 100-ohms. With this configuration, ISOM8110 can reach around 50kHz data rate. 

    However, if your controllers need a clean and fast digital output, ISOM8711 is preferred since it is designed for this purpose.

    Best,
    Andrew

  • 0 in reply to Andrew Jackiw
    Intellectual 532 points

    Hello ,

    Thanks for the details, one quick query - if I have a current pulse generating sensor, and all I want to isolate is these current pulses - not the magnitude the count of pulses being transmitted - can ISOM8110 be a good option in this use case? Am I thinking on the right lines?

  • 0 in reply to Neet
    Guru 267960 points

    The ISOM8110 is optimized for analog signals. When used with digital signals, the rise and fall times are asymmetrical because of its open-collector design. So it is not suitable when the pulse width matters. But if only the pulse frequency matters, then 44 kHz or 22 kHz would work with it.

  • 0 in reply to Clemens Ladisch
    TI__Expert 8365 points

    Hello,

    Thank you for your question. Please allow Andrew an additional day to respond.

    Regards,
    Aaditya Vittal

  • 0 in reply to Aaditya Vittal
    TI__Mastermind 18335 points

    Hello Neet,

    As Clemens said the ISOM8110 used as a digital signal will have noticeable asymmetry at higher speeds. Typically any signal below 50kHz is okay. ISOM8110 may be a good option for your application. 

    I would recommend ordering an EVM and changing the resistors to see if the wave forms are okay for your application. 

    Best,

    Andrew