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SN65HVD75: SN65HVD75

Artem Pinsky
Prodigy 20 points
Part Number: SN65HVD75

Tool/software:

Hi,

I am using SN65HVD75DGKR devices for RS-485 communication, some times I see different resistance on the A and B inputs referred to ground (pin 5) such as 220K and 1M.

I tend to think that 220K is the internal FET resistance, and when 1M , may be it means that there is a cutout in the transistor.

Can anyone advice and explain the difference in the resistances above ?

Thanks,

Artem.

  • 0
    TI__Guru 60880 points

    Hi Artem,

    I took a look at the datasheet but I don't really see where we specify 220k or 1M ohms, are you talking about another device or is this more of a general question about RS485 inputs?

    My guess may be that you're looking at part of the resistor divider network if it's on the A/B input stage.

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 20 points

    I have checked the resistance on the device itself without voltage.

    After having problems receiving the data, I suspect that something happened to the device, and after checking the resistance  I see difference on the not working device vs new device .

    Because I didn`t see this information in datasheet , thought here will someone shed light on the issue.

    Artem.

  • 0 in reply to Artem Pinsky
    TI__Guru 60880 points

    Hi Artem,

    Thanks for the additional information. We don't characterize our devices impedance levels so we don't have an accurate way of verifying if one of the two is damaged or broken based on the impedance readings. 

    There may be some sort of short somewhere due to damage on the device which is why the resistance reads a lower value. It's pretty hard to pinpoint root cause of damage to a device even when they go through FA (failure analysis). 

    Is it possible there was some kind of short on one of the pins during a hot insertion event? 

    Were you doing any kind of stress testing that involved ESD or some high transient? 

    Have you probed the A/B pins during operation to see if they swing as expected or if there is some overshoots/undershoots that shouldn't be there? 

    If you provide a schematic, I could try to see if there is anything wrong with it or that could potentially be a problem. 

    -Bobby