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THS5641A: Request for schematic review

Andrew Baek
Intellectual 905 points
Part Number: THS5641A
Other Parts Discussed in Thread: LMH6601, LMK04828

0410.FIBERSENSE_V1P07.pdf

Hello,

Could you review the schematic with THS5641A?

The circuit design is on Sheet 17.

Thank you,

Andrew

  • 0
    TI__Guru* 91947 points

    Andrew,

    1. Suggest adding series 22 ohm resistors and or a buffer to the data lines if the traces are long from the FPGA. Same for the CLK driver. 

    2. Add a 4.7uF and 0.1uF decoupling caps to AVDD pin 24. Place these and C332 close to the pin.

    3. Add bulk 10uF decoupling caps to both AVDD and DVDD. 

    3. Make sure all digital inputs meet the digital specs on sheet 6 of the data sheet.

    Regards,

    Jim 

  • 0 in reply to jim s
    Intellectual 905 points

    fibersense_v1p07a.pdf

    Jim,

    I think I have addressed all of your comments.

    In addition,

    • updated AVDD and DVDD to 3.3V
      • DVDD needs to be 3.3V so it can interface with FPGA bank running at 3.3V
      • AVDD can be 3.3V.  The LMH6001 can extend the voltage range if needed

    Please let me know of any additional feedback.

    Regards,

    Andrew

  • 0 in reply to Andrew Baek
    TI__Guru* 91947 points

    Andrew,

    1. I think you need to adjust the supplies on the LMH6601, as per the data sheet, V+ - V- must be no greater than +5.5V.

    2. Place R321-R329 as close as possible to the FPGA.

    3. The DAC performance may be reduced if the clock from the FPGA is noisy. Most customers do not use the FPGA for a clock source. 

    Regards,

    Jim

  • 0 in reply to jim s
    Intellectual 905 points

    Hi Jim,

    1. I have updated to a single supply design.  The edges of the square wave are not as sharp but acceptable.  I also have an option to use 5.0V as opposed to 3.3V.  Thanks for pointing out the V+ - V- being limited to 5.5 ~ 6V.
    2. I have moved them to the FPGA sheet. I'll let my PCB team know they need to be close to the FPGA
    3. The DAC clock is coming from the LMK04828 on Sheet 18.

    In terms of coupling between THS5641A and LMH6601, I have a resistor to the ground.  Now I am thinking I need a filter for anti-aliasing. Perhaps this would be question for LMH6601.

    Thank you,

    Andrew

  • 0 in reply to Andrew Baek
    Intellectual 905 points

    I forgot to add the updated schematic.  

    Here it is.

    FIBERSENSE_V1P10.pdf

  • 0 in reply to Andrew Baek
    TI__Guru* 91947 points

    Andrew,

    I am having someone from our amplifier team take a look at this as well. It may be a couple days before we get back to you.

    Regards,

    Jim 

  • 0 in reply to jim s
    Intellectual 905 points

    Hi Jim,

    I'm going to close this case, and open a new case for the amplifier separately.

    Thank again for your support.

    Regards,

    Andrew