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Hello,
We are using ISO3082 in Industrial environment for communication over fairly long distances of 300-500 meters at 9600bps. Here is the partial schematic,
Please note that we don't use the bias resistors and same board is also used with MAX14945EW+, depending on part availability. R62, R63 are 0E & R64 OPEN when ISO3082 is used.
We have so far used around 1200 ISO3082s over the last 12 months.But we're now seeing random failures of ISO3082, around 2-3 per month over last 3-4 months.
What could be causes of IC failure? What measures can we take to avoid or at least minimize the IC failures?
Thanks in advance,
Saumitra A Deshpande
Hi Saumitra,
Sorry to hear about the issue and thanks for reaching out.
The schematic looks good and I do not see any issues with it. To help debug the issue, could you please help us with below information.
I am not sure if it is an option for you at this time, ISO1410 is our latest RS-485 device that is pin compatible to ISO3082. ISO1410 has superior overall performance over ISO3082.
Please do help us with the requested information to debug the issue further, thanks.
Regards,
Koteshwar Rao
Hi Koteshwar,
Thanks for the reply.
Thanks,
Saumitra A Deshpande
Hi Saumitra,
Thanks for sharing additional information as requested, this helps me understand the situation better.
From the resistance values that you have shared and from the confirmation that you have provided that both working and non-working devices have the same I/O resistance to their respective grounds, it doesn't quite seem like the device is damaged. As a next step of debug, please do try to test the device and monitor input output waveform. If you do see anything unusual, please do share me the waveform.
I will also check with my other colleagues on this issue on Monday and see if I can provide any further debug steps. Thanks.
Regards,
Koteshwar Rao
Hi Saumitra,
Thank you for sharing the schematic and the debug information!
I want to point out that the TVS diode by itself isn't sufficient to protect the transceiver.
Based on the datasheet, the absolute maximum ratings for the bus pins are -9V and 14V.
The SM712 clamping voltages are 19V at 1A and 31V at 19A.
Therefore, we should place a 10ohm resistor between the bus pins and the TVS diode
to cause a voltage drop from the TVS diode to the bus pins. Please refer to this TI design
and section 9.2.2 of this datasheet for details.
Could you please perform a curve trace on bus pins of the damaged device and
a functioning device? We will have a better insight into the damaged device with this information.
Regards,
Alfred
Hi Saumitra,
As pointed out SM712 TVS diode by itself does not fully protect the BUS.
If you have a follow-up question, please use the Ask a related question button on the top right to post your question.
Regards,
Alfred