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ADS1299: What are the possible reasons for heating up of ADS1299?

Tech Turiya70
Prodigy 90 points
Part Number: ADS1299

Hello TI Team,

We are currently using an ADS1299 to acquire 8 channel data as in ADS1299EEGFE-PDK board.

To begin with, we referred to the datasheet for ADS1299 & ADS1299EEGFE-PDK board and made connections to each pin as per requirement. Further, when we supplied the ADS1299 with 5V and GND (Unipolar) as power supplies, it got heated up quickly. To troubleshoot it,  we proceeded with probe testing the connections made but all the connections were connected correctly and the voltages read were to the right values.

As an alternative, we provided the ADS1299 with 2.5V and -2.5V (Bipolar) supplies and as a result, we observed no heating up issue of the IC. We then proceeded further to tested our board for SPI communications (that worked perfectly for ADS1299FE Board as we were able to read a channel’s data correctly) and observed that the values of registers were read correctly but the data being received was intermittent.

Can you please let us know the possible reasons for the same?

Thanks!

P.S - Providing Bipolar supplies, the SPI clock signal was probed to compare with its ideal waveform: SPI Clock was similar to as seen from ADS1299FE Board.

  • 0
    TI__Guru**** 180961 points
    Hi Tech,

    Welcome to our e2e Forum. If you are using our ADS1299EEGFE-PDK, chances are good that you had some jumpers misplaced when operating with a uni-polar (0-5V) power source, please verify the positions of the shunts on JP2 and JP20. There is no other reason I can think of that might have caused the ADS1299 to heat up unless the power was inadvertently swapped, or something was mis-wired. If you are now getting intermittent data using the same chip that was overheated, you may have damaged the device.
  • 0
    Prodigy 90 points

    Part Number: ADS1299

    Hi TI team

    We have designed a board refering to the power supply circuits from MMB0 board and ads1299fe board. We probed the outputs of the power supply and we are getting 5v, 1.8v, 3.3v, 2.5v, -2.5v, and -5v at desired testpoints. We have also added planes for avss, agnd and avdd and followed the layout guidelines as given in ads1299 datasheet. We are using internal oscillator of the ads. We are facing following two problems:

    1. When we select avdd = 5v and avss = 0v, the ads chip starts heating rapidly. It does not heat at all when we use avdd = 2.5v and avss = -2.5v.

    2. With avdd = 2.5v and avss = -2.5v, we can read register values through spi port but the data rate is coming to be 60-70 SPS in comparison to 250 SPS for the ads1299fe board.

    We have kept all the 4 bias pins open as we didn’t feel the need. We did not use the bias signals even while working with the fe board.

    The ICs used for power supplies are:

    REG104GA, TPS60403DBVT, TPS72325DBVT, TPS73225DBVT, TPS70351PWP(used to generate 1.8v and 3.3v specifically)

    Other than these power ICs only ads1299 ic is on the board to implement very basic functioning of ads.

    What can we do to debug the issues?

  • 0 in reply to Tom Hendrick
    Prodigy 90 points
    The details are provided as below. Please note that we are not use ADS1299EEGFE-PDK. We have made a new board.
    Pasting the content here again:

    "Hi TI team

    We have designed a board refering to the power supply circuits from MMB0 board and ads1299fe board. We probed the outputs of the power supply and we are getting 5v, 1.8v, 3.3v, 2.5v, -2.5v, and -5v at desired testpoints. We have also added planes for avss, agnd and avdd and followed the layout guidelines as given in ads1299 datasheet. We are using internal oscillator of the ads. We are facing following two problems:

    1. When we select avdd = 5v and avss = 0v, the ads chip starts heating rapidly. It does not heat at all when we use avdd = 2.5v and avss = -2.5v.

    2. With avdd = 2.5v and avss = -2.5v, we can read register values through spi port but the data rate is coming to be 60-70 SPS in comparison to 250 SPS for the ads1299fe board.

    We have kept all the 4 bias pins open as we didn’t feel the need. We did not use the bias signals even while working with the fe board.

    The ICs used for power supplies are:

    REG104GA, TPS60403DBVT, TPS72325DBVT, TPS73225DBVT, TPS70351PWP(used to generate 1.8v and 3.3v specifically)

    Other than these power ICs only ads1299 ic is on the board to implement very basic functioning of ads.

    What can we do to debug the issues?"
  • 0 in reply to Tech Turiya70
    TI__Guru**** 180961 points

    Hi Tech,

    Can you provide your schematic?

  • 0 in reply to Tom Hendrick
    Prodigy 90 points
    Hi Tom,
    Following is further information on our debug:

    When I am supplying avdd=5V and avss=0V, without supplying dvdd (open), the ic is not heating. I.e. only analog power supply is given and ads is not heating. But as soon as I connect jumper to supply dvdd=3.3V, ads starts heating up.
    Also, we are getting hardly 5mV at VCAP1. I am guessing there might be some problem with our power up sequencing. We have pwdn and reset tied low at startup and we are switching on analog and digital power supply simultaneously. Do you see why vcap1 could be so low?
  • 0 in reply to Tech Turiya70
    TI__Guru**** 180961 points
    Hi Tech,

    A schematic would be helpful, I suspect you don't have your ground(s) set up right. Look through the schematics in the back of the ADS1299EEGFE-PDK manual and see how AVSS, AGND and DGND are configured when running in uni-polar versus bi-polar mode. Specifically R74, JP2, and JP20 - when 5V is used, AVSS becomes AGND and R74 ties AGND and DGND together.
  • 0 in reply to Tom Hendrick
    Prodigy 90 points
    Thanks for the quick response Tom.
    I will confirm this and get back.
  • 0 in reply to Tom Hendrick
    Prodigy 90 points

    6724.Schematic.pdf

    This is the schematic that we made.

  • 0 in reply to Tech Turiya70
    TI__Guru**** 180961 points
    Hi Tech,

    Did you ever resolve this issue? Your schematic is not easy to follow - are you sure that the various GND/DGND/AGND net names are actually connected on your board? I'm not familiar with how KiCad makes the associations across pages.