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ADS1278: During the use of ADS1278, some channels often burn out, resulting in - 10V

user3748446
Prodigy 30 points

Part Number: ADS1278

Hello everyone,

  I use the 8-channel data acquisition board designed by ADS1278. There are always some channel failures in the use of individual boards.

Fault phenomenon :

    if all channels are tested normal the day before, the output value of 1-2 channels will change to constant-10v when the machine is turned on the next day, the channel with fault is often the first channel and the second channel, and sometimes have other channels.

   My power supply is switch 220 to 12V with DCDC converter, and LDO is used for 5V, 3.3V and 1.8V.

I would like to know what causes this kind of failure

 thank you！！！

  • 0
    TI__Mastermind 49040 points

    Hello,

    Would it be possible to share part of the schematic that shows the ADS1278, reference circuit, and the input amplifiers?

    I assume that your full scale input range, before attenuation, can be as low as -10V. 

    What voltage is present on the analog inputs under this condition? 

    What is the CODE read from the ADC?  Does the ADS1278 recover after a power cycle, or is it permanently damaged?

    During power-up, if the analog inputs are driven with a voltage before the analog supply voltage ramps up, it can cause the device to lock up.  In this case, you would be violating the ABS MAX specification of the ADS1278.

    Analog input to AGND:  -0.3V to AVDD+0.3V

    Another common problem is ground bounce if using two different ground paths for the analog and digital grounds.  The ADS1278 is sensitive to any voltage difference more than 0.3V between AGND and DGND.  If these two pins are not directly tied to the same ground plane, power-up transients can exceed this requirement, possibly causing damage to the device.

    AGND to DGND:  -0.3V to +0.3V

    Regards,
    Keith Nicholas
    Precision ADC Applications

  • 0 in reply to Keith Nicholas
    Prodigy 30 points

    Hello Keith Nicholas.

         thank you very much for your reply! your reply is very helpful!

         i dont know how to insert sch to the page.

         1. the input amplifier is THS4521IDGK, the input voltage is about 2.2V  while it is left unconnect during testing.

         2. the CODE read from the ADC is normal for the Undamaged channels,  and always -10V for the damaged channel.

        3. in my Circuit,  the analog and digital grounds are isolated by a magnetic bead (GZ2012D101TF 100Ω ±25% 100MHz).  This may be the cause of the problem?????    

         So how can I improve this problem??   

         thanks again!!

  • 0 in reply to user3748446
    TI__Mastermind 49040 points

    Hello,

    Separate analog and digital grounds with a magnetic bead are the likely cause for damage.

    The analog and digital ground pins on the ADS1278 need to be connected to the same ground plane.  Since you have two separate planes, the best way to fix this is to connect the analog and digital ground planes directly together beneath the ADS1278.

    Please take a look at this post that goes into more detail on this subject.

    https://e2e.ti.com/support/data-converters/f/73/t/755516?-FAQ-PCB-Layout-Guidelines-and-Grounding-Recommendations-for-High-Resolution-ADCs

    For testing, you could replace the magnetic bead with a 0ohm short.  This should improve reliability, but to completely fix the problem, you should re-layout the board.

    Regards,
    Keith

  • 0 in reply to Keith Nicholas
    Prodigy 30 points

    Hello Keith!

        thank you very much! I'll re-layout the board.