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question about AFE5805 schematic

lutao wang
Prodigy 50 points

Other Parts Discussed in Thread: AFE5805

Hi,

    I am designing a ultrasound device now. In AFE5805 datasheet, it says that the pin VCA_CS# (H4) can be connected to pin RST(H5). Does this means these two pins can be connected directly? In AFE5805EVM user guide (SLOU222B), there is a resistior (the value is not indicated) between VCA_CS# and RST, and then VCA_CS# is connected to pin 9 of  FT245RL(U10), what does this mean? Does the RST(H5) of AFE5805 need any other control ? I use a fpga to capture the output data of AFE5805. In LVDS test patterns, the output of AFE5805 can be well  captured. But when working in normal mode, the input sine signals (1.5MHz, -10dBm) can not be  obtained in fpga. I connected   VCA_CS# directly to  RST(H5), and there is no any other pin was connected to these two pins. Does this wrong?

Thank you!

  • 0
    TI__Expert 6320 points

    Lutao,

    R26 between these two pins is 0ohm resistor, so they can be connected together.  You can power down the VCA by using the GUI and you should some current change on your power supply.  This will tell if you have good communication to the device.  Were you able to see the ramp test patterns?

    Thanks,

    Chuck Smyth

  • 0 in reply to Chuck Smyth
    Prodigy 50 points

    Hi Chuck,

          Thank you for your suggestions.  I have designed a new board accroading the schemetic of AFE5805EVM, and i use a xilinx FPGA to communicate with AFE5805. I saw the ramp test patterns using ChipScope. When i change de settings of AFE5805, the ramp test patterns also changed. So, I think there maybe no problems about the communications between AFE5805 and FPGA. But when i assigned a 1Mhz single tone signal to the input of AFE5805 and changed AFE5805 to normal operation mode, i can not see the input sine signal in ChipScope. I really do not know why?

    Thanks,

    Lutao Wang

  • 0 in reply to lutao wang
    TI__Expert 6320 points

    Lutao,

    I understand your frustration because that confuses me as well.  In ramp mode, all channels are outputting a ramp signal and in normal mode you probably have connected only one input and therefore will only see the sine wave on one channel.  Are you sure that you are looking at the right channel?  Do you see noise or just one value? 

    Chuck