This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

  • TI Thinks Resolved

ISO7720: ISO7720 application issue

Intellectual 1130 points

Replies: 10

Views: 260

Part Number: ISO7720

Hi teams

My customer has a new requirement I listed below:

3.3V(High)-0V(Low)input to 3.3V(High)-1V(Low) Output. 10Mbps data rate.

I have an idea to achieve this requirement with our ISO7720 and need to double confirm with you.

Below is my question:

  1. Could we supply the device with 3.3V to VCC2 and 1V to GND2 to achieve this? (3.3V and 0V is applied to VCC1)
  2. If it could will it output a low level with 1V in output?
  3. Could we generate the 1V from VCC1 to power GND2? (Customer didn't need isolation actually)

  • Hi Gabriel, 

    I think there may be an issue here. If you supply 3.3V to Vcc2 and 1V to GND2, you are essentially giving 2.3V power supply to the ISO7720. This is very close the the UVLO threshold which may mean if the power supply is not well regulated the device may get stuck in UVLO during normal operation. 

    For my understanding, can you explain why the LOW signal has to be shifted up to 1V instead of 0V?

    Best regards, 

    Dan

  • In reply to Dan Kisling:

    Hi Dan

    Customer end equipment is LED wall driver.

    They leverage a 4V bus for LED driver IC to control the LED current.

    But as R/G/B/W LED forward voltage is different so some specific color LED won need such large headroom voltage.

    They create a 1V GND voltage for some LED to reduce the headroom voltage.

    So for these LED driver the control signal GND is 1V.

    I have tried this connection in ISO7721 EVM but it didn't work.


    I increase the input voltage to 4.5V and leverage TLV62569 (non-isolated buck converter) to generate 1.5V output.

    Under this condition the supply voltage for ISO7721 is 3V. But after I connected 1.5V to GND2 the buck output will be pump to also 4V.

  • In reply to Gabriel Xu:

    Hi Gabriel, 

    Sorry for the delay in response - the US had a holiday weekend. 

    Would you be able to draw a quick schematic of what you have tried so far so I can analyze it further? 

    Best regards, 

    Dan

  • In reply to Dan Kisling:

    Hi Gabriel, 

    I haven't heard from you in a bit over a week. Were you able to determine a solution? 

    Best regards, 

    Dan

  • In reply to Dan Kisling:

    Dan

    As this solution didn't work and the cost is much higher than other solutions, customer transfer to the new solution

    ( We achieved the same functionality through 3-state buffer gate) 

    But I am still interested in why this circuit didn't work anyway. The connection diagram is shown below:

  • In reply to Gabriel Xu:

    Hi Gabriel, 

    Sorry for the delay in response. I just checked this configuration in the lab (see picture below) and was able to make a 1V to 4V output. 

    Best regards, 

    Dan

  • In reply to Dan Kisling:

    Hi Gabriel, 

    I made a mistake in the picture in my last post and had the ground from the scope connected to 1V instead of GND. I have now updated the picture in the above post so it is correct. 

    Best regards, 

    Dan

  • In reply to Dan Kisling:

    Hi Dan

    Which part are you used for this experiment? I test in ISO7721 EVM.

    I also wonder to know are PSU1-PSU2-PSU3 are both isolation power supply?

    As I use a non-isolate buck converter to convert 4V to 1V for floating ground power supply.

  • In reply to Gabriel Xu:

    Hi Gabriel,

    I am Manuel, a colleague of Daniel's; please allow me to continue this conversation while Dan is out of the office due to US holidays.

    I believe Daniel conducted the lab experiment on an ISO7741 EVM, which is the same technology as ISO7720 with only a different channel configuration. The 4V and 1V power supplies were isolated from the 5V power supply, but this is not a requirement for the experiment to work -- the three PSU GNDs could all be connected.

    Can you describe your system's actual behavior vs. expected? What are the device's inputs and outputs?

    Please also confirm the measured voltage levels between Vcc1 - GND1 and Vcc2 - GND2 are within the recommended supply voltage range.


    Thank you for your time,
    Manuel Chavez

  • In reply to Manuel Chavez:

    Hi Gabriel, 

    Thanks for your patience while I was out of office for the US holidays. 

    Manny is correct - I did conduct this experiment on ISO7741EVM but it would work for any ISO77xxEVM. The power supplies used do not have to be isolated. I also tried connecting all of the GNDs on the power supply and this experiment yielded the same result. 

    Best regards, 

    Dan

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.