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Do you have a high-speed part that combines isolation with level shifting?

Warren Massey
Prodigy 70 points
Other Parts Discussed in Thread: ISO6741, CD40109B

I've grown weary looking through your isolated products offerings trying to find something that, for TTL input levels, offered both isolation as well as level shifting over an output voltage range of 3-to18 volts.  To further complicate matters, I'd like it to be a relatively high-speed part with a propagation delay less than 200ns and H-to-L & L-to-H transition times less than 100ns.   Got anything?

  • 0
    TI__Genius 17825 points

    Hello,

    Thank you for your inquiry.

    Most of the digital isolators have two dies which can be independently powered. Due to this, the voltage levels of the two dies can be different voltages. Therefore, these digital isolators enable voltage level translation. Please share some more details on what voltage level translation you need.

    One of our popular digital isolators is the ISO67xx family and we believe that it could meet your requirements. As an example, the ISO6741 supports a data-rate of 50Mbps and a typical propagation delay of 11ns and a typical rise/fall time of about 3ns. Please take a look at this device and let us know if this meets your requirements.

    Regards,
    Aaditya Vittal

  • 0 in reply to Aaditya V.
    Prodigy 70 points

    Thanks for the reply but most of the digital isolators fall well short on the output side max-allowed output voltage.  I'm looking for something that can work for either 3.3v or 15v (max at 18v).  The ISO6741 tops out at 6v for Vcc2.

  • 0 in reply to Warren Massey
    TI__Genius 17825 points

    Hi Warren, 

    Thank you for your response.

    Since most digital CMOS/TTL logic signals are up to 5V, all of our digital isolators only support logic levels up to 5V. 

    Can you please clarify what the 15V is being interfaced to? The more information you share about your application, we will be able to make a better device recommendation.

    Regards,
    Aaditya Vittal

  • 0 in reply to Aaditya V.
    Prodigy 70 points

    "Can [I] clarify what the 15V is being interfaced to?"  No, not in any manner that you would find satisfying.  The part that I am seeking will be used to drive carefully-timed trigger pulses down various lengths (3-300 feet) of coax cable to a variety of devices (cameras and otherwise) that will take some action upon receiving a trigger.  The trigger inputs of the devices vary with the device and will vary from HCMOS inputs, to optoisolators to something else.  One specialty camera even uses a LT3008 as its receiver for the trigger input.  I cannot say what new devices might come along that have even weirder inputs so I just want to design for 3.3v on the low end and 15v on the high end.  A  CD40109B or HEF4104B appears to meet this requirement but they don't have the isolation component. 

    It's OK to say that TI has got nothing available with these characteristics, rather than trying to bend my requirements to fit your products. I just wanted to ask before moving on to another solution. Your web page parametric search utility makes it hard to get a broad view of all your isolation products along with filters that are important to me for this design (the filters are too customized by product line to be useful to me).

  • 0 in reply to Warren Massey
    TI__Guru 55815 points

    Hi Warren,

    Thank you for your further inputs and clarifications, appreciate it.

    Like you have already found out, we currently do not have isolators that supports I/O voltages >5V. There maybe many non-isolated translation devices or output drivers that support driving 18V output signals which could accept 3.3V signals and generate 18V outputs. You could pair a digital isolator with a translator or an output driver to achieve the function. You could post non-isolated voltage translator and output driver questions at the following forums, respectively.

    https://e2e.ti.com/support/logic-group/logic/f/logic-forum

    https://e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum

    I understand you were looking for a single-chip solution but we currently do not have such a device and the suggested 2-chip alternatives are the best we have. Thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 70 points

    First of all, at the outset I said that I hoped to drive the isolator with TTL (5v) not 3.3v.  The 3.3v was an output capability for when I needed to interface to HCMOS.

    Strictly speaking, you do have isolated gate drivers that can reach 15v or 18v on their outputs, but they don't go as low as the 3.3v so they are not a good fit.

    What I really need is an isolated-level-shifter-forum but that does not appear to be an option at this time. Too bad, I think it would be generally useful.

  • 0 in reply to Warren Massey
    TI__Guru 55815 points

    Hi Warren,

    Thanks for clarifying that you would like the output voltage to support the range of 3V to 18V while input is 5V TTL.

    Your understanding is correct on the isolated gate drivers, these products (along with non-isolated output driver) are supported by the motor driver forum and that is also the reason I suggested you to post this question to motor driver forum.

    The forums are broadly classified so that the E2E users do not need to worry about if they are posting the question in right post. The forums have many product groups included and you should get suggestions for level shifters and isolated level shifters (if one exists) from the two forums I suggested. Since an isolated level shifter is both an isolator and a level shifter, such a product could exist in either of the product groups. We do not have this, I am hoping the level shifter or motor driver product groups may have a better solution for you.

    Please feel free to post your question on those forums and you will be provided with the best possible options based on which you can decide if it fits your requirements. Thanks again.


    Regards,
    Koteshwar Rao