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ADS8342 running hot when supplied with -5V

Aditya Gaddam
Intellectual 850 points
Other Parts Discussed in Thread: ADS8342

Hi,

I am trying to use the ADS8342 with the schematic setup according to help from a previous post here: http://e2e.ti.com/forums/p/10474/40988.aspx#40988

However, when I power the board up with -5V connected to -DVDD and -AVDD, the ADC pulls about 350mA and runs very... very hot. If I connect these pins to GND however, it only draws about 50mA and is running at a decent temperature. Not completely cold still but it's barely warm. What could cause the chip to do this? I made sure there are no shorts between any of the rails. The other end is 5V for DVDD and AVDD. 

 I have uploaded a screenshot of the schematic here: http://upload.pixelfaction.com/files/4b1e9402_ads8342.png

(Note: I know C46/48/50/52 are on backwards in the schematic, but I have soldered them the right way on the actual board).

(Note: Also, the input to the DVDD/AVDD area on the top left gets -5V in the schematic, but I corrected this on the board with a jumper. Initially though thtat was the problem, but it still draws a lot of current / gets hot )

 

Any help would be appreciated.

 

Thanks,

Aditya

  • 0
    Intellectual 850 points

    Anyone? I've also found out today that the BUSY pin is stuck at 2.2V for some reason. BVDD is at 3.3 as the schematic above shows. 

     

    Any help would be really appreciated.

  • 0 in reply to Aditya Gaddam
    TI__Guru**** 180941 points

    Hi Aditya,

    I've gone over your schematics and can see no reason for the device to be getting hot.  One question I have for you, you mentioned that the device had -5V initially applied to the AVdd and DVdd inputs but that you fixed that on the board with a jumper.  Did you replace the original chip as well or is this the same device that had the -5V applied to DVDD/AVDD?

  • 0 in reply to Tom Hendrick
    Intellectual 850 points

    I've changed the chip since fixing the short. I actually took the ADC chip off to make suer it was the ADC pulling the current as opposed to the opamps I have on the board. That's when I noticed the DVDD/AVDD thing. So once I fixed the short, I soldered on a fresh piece. 

  • 0 in reply to Aditya Gaddam
    TI__Guru**** 180941 points

    Hi Aditya,

    I've got one of the EVMs for the ADS8342 running in our lab now.  The current draw on the +/-5V supplies are both on the order of 25mA.  The schematic for this board is located in the back of the users guide for the EVM, which you can review here:

    http://focus.ti.com/lit/ug/slau120/slau120.pdf

    There really is not that much different in the power area from your schematic to ours so I am not sure where to tell you to look for the problem.  I've tried powering up the board in several different ways and never see the (-) supply draw any additional current.   All I can do at the moment is ask you to verify the grounds (analog and digital) are connected together and verify there are no solder shorts on the board.