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SN65HVD72: SN65HVD72DR

Parvin Sherakar
Prodigy 40 points
Part Number: SN65HVD72

Tool/software:

Hi,

Our current design uses ST1480ABDR IC from ST. We have found that, few PCBs failed to work.

This is easy to reproduce at 70 degC. Problem can be seen within 2 hours After some research I found that, in some applications the fail safe bias resistors are require at A and B.

I tested with external fail safe resistors with ST part ST1480ABDR and the problem was resolved.

Now , we have thousands of PCBs made for our production. so I decided to use SN65HVD72DR TI part with internal bias resistors.

When I tested at 70 deg with two different PCBs, One PCB worked well without any issues. second PCBs failed after 8 hours.

Could you please help me to check this issue? Does this IC also need external Bias resistors?

If you can provide an email address, I will share the schematics. this issue is urgent as our production is on hold now.

Thanks

Parvin

  • 0
    Guru 316920 points

    Both the ST1480Ax and the SN65HVD72 have fail-safe inputs that output high when the differential input voltage is zero, with a tolerance of about 15 mV/20 mV for the ST/TI devices. Apparently, you have noise that is higher. If you need external bias resistors to get a correct voltage with the ST1480AB, then you will also need them with the SN65HVD72.

  • +1
    TI__Guru 73181 points

    Hi Parvin,

    As Clemens pointed out, both devices have something called internal fail safe protection which pushes the VIT+ to a negative voltage which helps keep R outputting high during shorts, open, and idle cases. But noise that exceeds the VIT- parameter could still cause glitches (When the noise is differential and makes A-B larger than -200mV). If adding the external resistors fixes this, then it means that you need external components to bias A-B to keep it larger than 0V because the noise in your system is too large without it. 

    -Bobby