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ISO35: Receiver common mode voltage spec

Luke Sun
Intellectual 1830 points
Part Number: ISO35

Hi team,

My customer met a strange issue when using ISO35 in -40C ambient temperature.

They found when the input common voltage of A/B signal is 1.2~1.4V (Case1), the device won't work correctly. ISO35 output is always constant even input is toggling.

But when the input common voltage becomes 1.75V~2V (Case2), the device could work correctly. Detail test condition is as below.

A

B

A-B

H

L

H

L

H

L

Status

Case 1

2.1V

0.7V

1.9V

0.5V

1.5V

-1.2V

No output

Case 2

2.7V

1.3V

2.5V

1.0V

1.6V

-1.2V

Normal output

My question is, does our device have a regulation on the receiver common input voltage?

Thank you!

  • 0
    TI__Intellectual 2900 points

    Hi Luke,

    The ISO35 is expected to support common mode voltages from -7V to 12V at -40C ambient temperature. (Referring to Section 7.3 in ISO35 datasheet)

    To get more clarity could you please help us out with the following?

    1. Do you have a schematic of the test circuit used for the experiment?
    2. Was there anything else connected on the bus lines other than the ISO35 IC? This would become clear once the schematic is shared.
    3. Were the voltages mentioned in the previous post measured at the A,B nodes directly on the IC pins?
    1. If not could you please measure the voltages directly at the IC pins or very close to the IC pins?

    Regards,
    Anand Reghunathan