ADXL355 Latch-up condition

Dear ADI support,

 

We have been using ADXL355BEZ in our condition monitoring (vibration transducer) products for a while, we’ve sold about 1000+ of them now.

 

We recently discovered that some of them fail strangely – they report a near-zero vibration (the AC part) - after experiencing a period of over-range high-frequency vibration. We initially suspects our firmware might have bugs, but after some research, we are now quite confident that it’s caused by the defects of ADXL355.

 

We know that ADXL355 has over-range protection mechanism when experiencing excessive accelerations. When activated, the output will be pulled towards midscale in order to protect itself. This is acceptable. But in some rare cases, this condition will persist even after power is re-cycled. The only way to bring the device back to normal is to tap it (or knock it, if you will) with a screwdriver or something.

 

While in latch-up condition, the ADXL355’s output consist of a fixed DC acceleration (in our two cases, it’s around -5g in x-axis. (we didn’t investigate other axis). On top of that, there’s also a high-frequency (around 1.6Khz) AC content, measured around 3.9g rms.

 

As I said previously, the condition is only cleared when external shock is applied. We did not try issuing self-test command. We’ll investigate more if you need more information. I’ll keep you up to date.

  • We have the same exact issue spanning across a considerable number of sensor nodes. We have definitively confirmed that the X/Y channels on ADXL355's are either:

    1. entirely stuck at the user set G range value

    2. intermittently stuck

    3. reporting very low vibrations whilst the Z axis is operating normally. 

    This has occurred on multiple ADXL355 sensors across multiple customer sites. The failure mode can be turned on/off repeatedly with a low transient shock ( < 8 Gs). The error does not relate at all to firmware since the failure mode was repeated using Analog's EVAL-ADICUP360 demo board. We are working with Analog Devices to resolve the issue but no resolution in sight..

    Feel free to contact me at: robert.cachro@dynapar.com

  • 0
    •  Analog Employees 
    on Jul 29, 2019 8:53 AM

    Hi

    Thank you for your query. Could you please explain your current setup to us? 

    Warm Regards, 
    John

  • 0
    •  Analog Employees 
    on Jul 30, 2019 3:51 AM in reply to John.Tuazon

    Hi

    May we also know how long have you used the device and also, do you have a rough estimate how over-range is the acceleration experienced by the device? 

    Warm Regards,
    John

  • 0
    •  Analog Employees 
    on Aug 1, 2019 3:07 AM in reply to John.Tuazon

    Hi , ,

    As stipulated in the datasheet, you should not subject the device to accelerations exceeding +/- 8g. The ADXL356/357 offers higher g ranges which may be suitable for your application. 

    Warm Regards,
    John

  • For a select group of sensors, we can definitively confirm that they were not subjected to an acceleration higher than the rated specification; both during production and at the customer site. In these controlled tests, the sensors were mounted rigidly to an asset at a customer site and operated correctly for an extended period of time. The acceleration levels experienced by the sensor can be confirmed by reviewing time-waveform acceleration trend data which clearly indicates operation at a safe level for a few months followed by the failure mode reappearing randomly. To your point regarding the spec, I have tested a few dozen sensors which have been subjected to levels of acceleration much higher than the specification rating, and the failure mode these exhibit is different from the ones I see in the former failure mode. The former failure mode can be 'turned' on/off by exposing the sensor to a high transient shock which is not true of the latter.