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THVD1551: About ESD contact discharge test of the THVD1551 chip

Jojo Wang
Prodigy 150 points
Part Number: THVD1551
Other Parts Discussed in Thread: STRIKE

Hi,

It is well known that electronic products need to be tested before leaving the factory.When I took an electrostatic gun and performed an ESD contact discharge test on the unshielded communication bus of the THVD1551 chip, the 6KV ESD contact discharge caused some errors in the data at the receiving end.Is the experiment I described above different from your?What test specifications should I follow in order to make the test result close to the 18KV ESD contact discharge?Please correct my test error. 

  • 0
    TI__Guru 62910 points
    Hello,

    The ESD specifications in the datasheet represents the threshold above which permanent damage to the device may be expected. Within this range, temporary communication errors can occur and are generally expected. (The presence of an ESD strike would typically raise the voltage on the interface bus to levels far outside the normal recommended operating range needed for proper communication.)

    Did the errors you see resolve themselves automatically, or did you observe any kind of permanent damage to the ICs?

    Regards,
    Max
  • 0
    Prodigy 150 points
    Hello,
    The 6KV ESD contact discharge often makes the emitted data inconsistent with the received data. No damage to the ICs.If the communication bus uses shielded cables, the antistatic capability will be much stronger.
    So, which test specification should I use, the results will be close to the ESD specifications in the datasheet?
    Regards,
    Jojo
  • 0 in reply to Max Robertson
    Prodigy 150 points
    Hi,Max
    The 6KV ESD contact discharge often makes the emitted data inconsistent with the received data. No damage to the ICs.If the communication bus uses shielded cables, the antistatic capability will be much stronger.
    So, which test specification should I use, the results will be close to the ESD specifications in the datasheet?
  • 0 in reply to Jojo Wang
    TI__Guru 62910 points
    Jojo,

    When we evaluated this device for IEC 61000-4-2 ESD, we placed the IC on its evaluation module and discharged the ESD generator on the relevant signal traces (typically a few cm away from the device). After the strikes at each level, we verified that there was no loss of functionality or parametric shift. Does this answer your question?

    Max
  • 0 in reply to Max Robertson
    Prodigy 150 points
    Max,
    Thank you for your careful answers, so that I have a certain understanding of ESD. But I am still somewhat confused about some experimental details, for example, whether the communication bus uses earth shield during ESD experiments. And can the ESD generator directly face the communication bus for contact discharge test?

    Jojo
  • 0 in reply to Jojo Wang
    TI__Guru 62910 points
    Hi Jojo,

    The ESD generator directly contacted the communication lines (A or B signals) for the contact discharge test. The ground return line of the ESD generator was connected to the same electrical net as the GND pin of the RS-485 transceiver, and an additional earth shield was not used (since the test was conducted directly on an exposed PCB with no enclosure or cabling connected).

    Max
  • 0 in reply to Max Robertson
    Prodigy 150 points

    Hi Max,

    Regardless of the voltage level of the air gap discharge, as long as the ESD generator discharges to the 422 communication bus and generates an arc, the communication data is disturbed.Therefore, when conducting ESD air gap discharge experiments, does the round head of the ESD generator's electrostatic gun keep a certain distance from the 422 bus to avoid arcing and discharge to the bus?So, how should we control this distance during the air discharge experiment?

    Jojo

  • 0 in reply to Jojo Wang
    TI__Guru 62910 points

    Hi Jojo,

    The arc that occurs is required for the air discharge tests, so you shouldn't try to avoid it.  An air discharge occurs when the spherical tip of the ESD simulator is in close enough proximity to the conductor that the electric field strength exceeds the threshold for dielectric breakdown, causing the air to ionize and form a temporary conduction path for current (carried by the arc itself).  Therefore, the test is conducted by first triggering the ESD simulator and then moving the tip of the gun towards the discharge point until an arc occurs.  Then, the gun is moved away, retriggered, and the process repeats.

    When the discharge occurs to communication lines (or other signals relevant to data transfer, such as the ground references or power supplies used by the transceiver circuits and UARTs), then it is expected for communication errors to occur during the discharge event.  The system should be able to recover without operator intervention in a reasonably short amount of time, though.

    Regards,
    Max