• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 33 subscribers
  • Views 519 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

ISO1540: connection of the two sides

Aurelia Pusino
Prodigy 10 points
Other Parts Discussed in Thread: ISO1540, ISO1541

About the ISO1540, I would like to connect the side 1 on the I2C bus, and the side 2 on a device, because the Vil_max of the device is 0.8V, as the maximum Vol of the ISO1540 on side 1.

I've read on the datasheet to connect side 1 on the device, and side 2 on the bus, but in this way the noise margin would be zero, so I couldn't use the ISO1540.

I would like to know if I can swap the two side, and if there are some adverse side effects. 

Thanks,

 Aurelia

  • 0
    TI__Mastermind 21800 points

    Hi Aurelia,

    To prevent latch up on the device, there had to be a mechanism implemented that allowed the device to differentiate between a low input from some other device, and a low output from itself, and this was implemented on side 1 of the device.

    Since the ISO1540 and ISO1541 basically limit the output voltage on one side to one diode drop above ground, this output side in turn becomes less tolerant to noise. Strictly speaking, by limiting the low output voltage, and having a possible VOL greater than 0.4 volts, side 1 is I2C compatible, but not compliant. Therefore, we recommend using Side 2, which has a lower output voltage, and is compliant to the I2C standard, for the bus side of the system, and Side 1 to be placed close to the local microcontroller in the system

    With that being said, I believe that the device will still operate in the system reversed. It will just be less tolerant to noise, and you will need to verify all the other devices that are attached to the bus are capable of handling the higher VOL voltage.

    Thanks,

    John

  • 0
    Expert 2585 points

    Hi Aurela,

    In your case I don't see  issue to  use ISO1540 with device on the side 1. As you mention V il_max of the device is 0.8V. But if you look to the  ISO1540 you will see VOL1(max)=0.8V too. Thus it should be ok.

    As well in this case if you don't need multimaster solution you could use ISO1541 and optimize  your system price.

  • 0 in reply to Oleksiy Pazyuk
    TI__Mastermind 21800 points

    Hi Aurela,

    To Oleksiy's point, we are guaranteeing the device outputs a maximum of 800mV. This is across voltage, process and temperature. We have built in margin to the parameter, so you should be fine without having additional margin.

    Thank you Oleksiy.

    John