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ADS1278: overheating and damaging device

Andrew Liu74
Intellectual 970 points
Part Number: ADS1278

Dears ，I use ADS1278  as ADC , but power on the pcb ,The ADS1278 will be very hot ,some times later ,the ADS1278 some channel be demaged . the sch as file ,please help review sch ,If any wrong ? many thanks ~

8KI4KO_MAIN_SCH.pdf

  • 0
    TI__Mastermind 46380 points
    Hello Andrew,

    The device is going into a latch-up mode due to some type of electrical overstress (EOS) event. The most common cause for this in the ADS1278 is when the AGND and DGND exceed the ABS MAX specification of +/-0.3V relative to each other.

    I see in your schematic that you have either a ferrite or coil inductor (LB2) between AGND and DGND. At a minimum, this should be a 0ohm short. However, depending on how far away the grounds are connected from the ADS1278, this may still not be good enough to prevent latch-up. Please refer to this post for more details.

    e2e.ti.com/.../2545203

    Ideally, all grounds on the ADS1278 are connected to the thermal pad, and then multiple vias are used to tie the thermal pad to the ground plane.

    You can try shorting LB2 to see if this helps, but you may need to change your layout as detailed in the above e2e post.

    Regards,
    Keith N.
    Precision ADC Applications
  • 0 in reply to Keith Nicholas
    Intellectual 970 points

    Dear Keith

    Thanks for your help , the pcb  layout file as the fellow , Description: When power on the pcb ,there is   one channel can not be work randomly, then overheat , if not power off ,the device will be damaged.

    I short the LB2 ,it is no effect , if there any other advice ,many thanks ~

    KIKO_MAIN.pdf

  • 0 in reply to Andrew Liu74
    TI__Mastermind 46380 points

    Hello Andrew,

    There are no bypass capacitors on the DVDD and IOVDD pins.  You should add at least one 10uF and 0.1uF next to the DVDD pins and another 10uF and 0.1uF next to the IOVDD pins.  There may be a large voltage transient during power-up without these capacitors; the IOVDD supply is nominal 3.3V, and has an ABS MAX spec of 3.6V.

    LB2 should be replaced as a short (0ohm) for your existing board design, but if you design another board revision, the AGND and GND planes should be connected directly together beneath the ADS1278, as shown below.

    Also, if the part was hot to the touch, then it is likely permanently damaged and will need replaced.

    Regards,
    Keith N.

  • 0 in reply to Keith Nicholas
    Intellectual 970 points
    Dear Keith
    Thanks for your help ! We test the ADS1278 as your advice , But the hot and demage phenomenon still exist , the IOVDD is 3.2-3.3V , is there any other advice , many thanks ~
  • 0 in reply to Andrew Liu74
    TI__Mastermind 46380 points
    Hi Andrew,

    I assume you modified a board with additional bypass capacitors on the supply pins. You will also need to replace the ADS1278 once it gets hot

    There is an over-voltage event occurring somewhere in the system. This could still be related to separate grounds at the ADS1278; any ground bounce due to external transients exceeding the ABS value of +/-0.3V AGND->DGND can cause latch-up and internal heating of device. You may need to redo the board layout to get this working.

    Have you confirmed the following?
    1. Verify all voltages under normal conditions are within the allowable ranges specified in the datasheet?
    2. Verify that the supply voltages during power-up do not exceed the ABS max levels? Specifically, does the IOVDD voltage at the IC stay below 3.6V during power-up?
    3. Verify that the +5VA does not exceed 5.5V during power-up. There are a lot of isolated DC/DC converters for the 5V isolation supplies; does the +5VA remain within limits when these supplies are enabled?

    Regards,
    Keith N.
  • 0 in reply to Keith Nicholas
    TI__Mastermind 46380 points
    Hi Andrew,

    I am going to close this thread out. If you have further questions, please feel free to repost.

    Thank you,
    Keith