• State TI Thinks Resolved
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 15 subscribers
  • Views 68 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

Original question:

ISO1640: Isolator I2C IC Check

ISO1640: I2C rise time is too long and input signal wave issue

hao Su
Intellectual 540 points
Part Number: ISO1640
Other Parts Discussed in Thread: PGA900

Tool/software:

Hi:

I use ISO1640 as I2C output isolator for PGA900.

But I find I2C SDA rise time is too long. PGA900 SDA rise time is about 240ns without IS01640 in 400KHZ.

But when I connect the PGA900 i2c to ISO1640, the rise time will be 360ns that is longer than 300ns.

I find there is strong wave on input SDA signal ,like the picture, there is 110ns flat wave part which make the rise time be longer than 300ns.

How can I reduce the rise time?

I have try to change R3 R5 from 100OHM to 0ohm but helpless for this issue.

  • 0
    Guru 298130 points

    This is the propagation delay through the isolator; you cannot avoid it.

  • 0
    TI__Intellectual 1965 points

    Hi Su,

    Thanks for reaching out. Please find my inputs below:

    The 110ns flat portion in the waveform is a characteristic of the device timing performance, mentioned a tLOOP1 in Datasheet as well:

    For more clarity, please refer to section 8.5 which explains this delay and how it is dependent on the device architecture.

    Regards
    Varun
  • 0 in reply to Varun Kumar
    Intellectual 540 points

    Thank you , I reduced the pull up resistor value make the rise time meet I2C spec.