Application questions about AD9249

Hi,

I want to design a 10-channel data acquisition circuit with AD9249. There are two quesions:

1、AD9249 has 16-channel. What should I do with the unused analog input VIN− and VIN+? Tied to GND, or just left floating?

2、What should I do with the unused digital output D− and D+? Left floating?

3、I must use dc coupled input, so balun and transformer will not work. Is ADA4932-1 suitable to drive AD9249?

Thanks

Zhao

  • +1
    •  Analog Employees 
    on Aug 21, 2020 5:05 AM

    Hi Zhao,

    Thank you for your interest in AD9249.

    For question 1 and 2, you can power down unused AD9249 channels. In that case there is no problem to leave the unused inputs and outputs floating. If this is of interest to you I can show you how to do this. You will need SPI communication.

    For question 3, the ADA4930 does not need a negative supply for its output common mode voltage to match the input common mode voltage of the AD9249. So from that perspective the ADA4930 is more compatible with AD9249.

    What is the maximum frequency of your signal?

    Thank you.

    Doug

  • Hi Dougl,

    Thank you for your reply.

    The trouble is that we don't really want to use the SPI communication. Is it safe to leave unused inputs and outputs floating if I do not power down the unused AD9249 channels? Or it just consume more power?

    We have two kinds of signal.

    First is a series of pulses. One point is collected for each pulse. Bandwidth of the amplifier could usually meet my requirement. 

    Second is sine wave. The maximum frequency is 400kHz. In this case, the signal is bipolar. Could ADA4930 convert the bipolar input without negative supply?

    Thank you.

    Zhao

  • 0
    •  Analog Employees 
    on Aug 21, 2020 10:40 PM in reply to ZhaoC

    Hi Zhao,

    You can leave the inputs and outputs of unused AD9249 channels floating without powering them down.

    Is your sinusoidal signal single-ended and swings positive and negative?

    Thank you.

    Doug

  • Hi Doug,

    Yes, my sinusoidal signal is single-ended and swings from 1V and -1V.

    Thank you.

    Zhao

  • +1
    •  Analog Employees 
    on Aug 22, 2020 12:16 AM in reply to ZhaoC

    Hi Zhao,

    For a single-ended sinusoid swinging from 1V to -1V you'll need a negative supply. ADA4932 is lower power and your signal frequency is low, so it sounds like ADA4932 is a better choice from that perspective.

    Thanks,

    Doug