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ADS5282EVM Single ended input configuration drawing 40mA?

pavanbabut
Prodigy 140 points
Other Parts Discussed in Thread: ADS5282EVM, ADS5282, AFE5801

Hello,

I am trying to use ADS5282EVM module with the following connected/modified
1) Power supply connected to 5V at J1 and J2
2) USB connected to PC along with TI software installed
3) J8 connected to a Xilinx ML605 LPC connector
4) CLKIN (J8) connected to a SMA connector on ML605
5) Removed T1, T2, T3, T4, T5, T7 (transformer), shorted Pins 1,6 and 3,4 of each transformer.
6) Input analog signal connected to IN1-P

When I turn on everything, the IN1-P is drawing about 40mA at 2V and about 19mA at 1V which seems a lot. It does the same on any INx-P (x-1:6). Is there any other better way to connect this the way we want it to use?

thanks

  • 0
    TI__Mastermind 29220 points

    Hi,

    There is a 50 ohm termination resistor shown in R7, which would result in 40 mA from a 2V signal across it, so that seems right to me.  Maybe you don't need the termination resistor if what you are doing is DC or very low frequency.

    Regards,

    Richard P.

  • 0 in reply to Richard Prentice
    Prodigy 140 points

    Thanks for your reply Richard. I see in the datasheet of ADS5282 that the  Analog Input Full-Scale Range: 2V PP and then in maximum ratings table it says -0.3V to 3.6V, can I use DC to 3.3V (0-3.3V) signal as input?

  • 0 in reply to pavanbabut
    TI__Mastermind 29220 points

    Hi,

    The absolute max limits mean that outside of that range you may permanently damage the device.    That does not imply that you can see normal operation on a such a range of conditions.

    The analog inputs are made to expect a fully differential input of 2V *peak-to-peak* and biased to a level within the recommended range for VCM.   That means that for a VCM=1.5V, then each side of the differential input has a 1V swing about that 1.5V VCM.    That is, at any instant the volatge on one fo the two input pins is within +/- 0.5V of the VCM, or in the range of 1.0V to 2.0V, and that the IN+ voltage is always the same amount above VCM as the IN- input is below VCM.

    This class of device is not made to operate with a single ended input on one input pin of the ADC.  

    Regards,

    Richard P.

  • 0 in reply to Richard Prentice
    Prodigy 140 points
    Ok, I think I can just use a divider circuit for my input signals to convert to 1.5V. Would you suggest any other device that we can use with signals like we have in our setup (single ended DC to 2V) at about the same sampling rate of 5282?

    thanks
  • 0 in reply to pavanbabut
    TI__Mastermind 29220 points

    Hi,

    No, at sampling rates around that rate (50Msps or more) I don't know of any ADCs that would take a single ended input.  Our EVMs are usually designed to take a single ended input from a piece of test equipment such as a signal generator and then we have a signal conditioning circuit to do single ended to differential conversion followed by biasing the signal to the desired VCM.  Usually this signal conditioning is done by transformer coupling, but when the signal bandwidth needs to go down to DC then we can't use a transformer and must use an amplifier circuit. 

    So you may want to look at our AFE devices (analog front end) that include an amplifier plus an ADC such as the AFE5801.  That is an octal ADC but with an amp on each channel that can be used wth a single ended input.   You would ask about such a device in the Medical Forum rather than this High Speed Data Converter forum because those devices are supported by the Medical group.

    Regards,

    Richard P.