Part Number: ISO7763
Other Parts Discussed in Thread: ISO6041
Hello TI,
I would like to raise a potential issue concerning the ISO7763FDW digital isolator and request your assistance in investigating whether there may be a batch-specific performance issue.
As shown in the attached schematic (EDA-04472-V3-0_sch.pdf), IC8 is the ISO7763FDW, connected in accordance with the recommendations in the datasheet.
The design was originally developed several years ago, and we previously manufactured a number of PCBs using this device without encountering any issues. More recently, we have produced additional PCBs using the same design: one production run through our internal electronics manufacturing facility and another through Eurocircuits. Both batches were fully assembled, and we have observed unexpected behaviour on the newly produced boards.
During testing with an oscilloscope, we have observed the following:
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At 40 MHz, the device appears to operate correctly.
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At 80 MHz, the signal from +2.5V to +3.3V continues to operate correctly, but the return path exhibits abnormal behaviour, appearing to miss clock cycles.
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This behaviour has only been observed on the recently manufactured PCBs.
We have investigated this by testing multiple PCBs and multiple ISO7763FDW devices from the recent production. The devices are from batches 52A32JK and 52A32KK, and the same behaviour has been observed consistently. As seen in this screenshot at 40MHz:
the results look ok, but at 80MHz, this is the result:
almost like it is missing clock cycles.
Fortunately, we still had devices from an older batch, 46ALN1K, available in our laboratory. We replaced the ISO7763FDW on one of the affected PCBs with a device from this older batch, while keeping all other components, test equipment and conditions unchanged. The issue immediately disappeared, and the circuit operated correctly at both 40 MHz and 80 MHz. We have tried using multiple old components on multiple of the newly produced PCBs, and these all perform perfectly.
Based on this testing, we currently have a strong indication that the issue may be related to the particular batches of ISO7763FDW devices rather than the PCB design or the wider test setup.
Could you please investigate the following:
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Whether batches 52A32JK and 52A32KK have undergone the expected production and electrical testing.
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Whether you can provide any relevant production, quality or test data for these batches.
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Whether there are any known issues, deviations or changes associated with these batches that could potentially affect high-frequency signal integrity or propagation performance.
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Whether TI has received any other reports of similar behaviour associated with these or neighbouring production lots.
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Whether you can recommend any additional tests that we should perform to further characterise or confirm the issue.
We are currently investigating this during the prototype testing phase. However, this is particularly important for us because we expect to procure approximately 4,000 ISO7763FDW devices over the coming months for production. We therefore need to establish with confidence that the devices we procure will provide consistent performance and that we will not encounter the same issue in production.
We would greatly appreciate it if TI could open an investigation into this matter and provide us with any information or recommendations that could help us identify the root cause and determine an appropriate way forward.
I have provided the PCB schematics, oscilloscope screenshots and batch numbers, but please let me know if you require any additional information to support the investigation.
Thank you in advance for your assistance, and I look forward to hearing from you.
Kind regards,
Geoffrey Morris
