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DAC8775: About schematic

tsuyoshi tokumoto
Expert 2630 points
Part Number: DAC8775
Other Parts Discussed in Thread: REF5050, TIPD216

Hi team,

 My customer is designing a schematic for a prototype including DAC8775.
 I am supposed to suggest a reference schematic to customer on Jan 9.
 Since I attached the schematic that I thought, would you mind
 checking it?

     Schematic of DAC8775.xlsx

 In addition,the design spec is as follows.
   Vin：15V(Single supply)
　 Output：0～20mA(4ch)
　　　　　*Voltage output stage is not used.
   External load：450Ω max
   HART interface：not used
　 Back-Boost converter：not used
 
 
Sincerely,
Tsuyoshi Tokumoto

  • 0
    TI__Genius 11750 points
    Howdy Tokumoto-san,

    I will gladly review your schematic, and will provide you with feedback once my review is complete. I'm currently traveling for the holidays, but expect to send the response within the next few days.

    Thank you for your patience,
    Matthew Sauceda
  • 0 in reply to Matthew Sauceda
    Expert 2630 points

    Hello Sauceda-san,

      Thank you very much for your quick response in spite of a holiday.
      I look forward to your advise.

      I hope you will have a nice holiday!

    Thank you and best regards,
    Tsuyoshi Tokumoto

  • 0 in reply to tsuyoshi tokumoto
    TI__Genius 11750 points

    Hi Tokumoto-san,

    Overall, great job, the schematic looks good, however there is one important finding that I wanted to verify, and that is the connection scheme of REFOUT to REFIN.

    • I've noticed that you are using  REF5050 for the external reference. Please ensure that the '0' ohm shunt connecting REFOUT to REFIN is not populated when using this external reference. The external reference should only directly connect to the REFIN pin.
    • I've also verified that the output range being used doesn't interfere with the compliance voltage required for normal operation. For instance, a maximum 20mA sourced current will create a total (450+15)*0.02A = 9.3V when probing the IOUT pin with respect to ground. The datasheet specifies that the maximum voltage on IOUT to maintain compliance is (VPOSIN - 3V), which is 12V in this case. Therefore, theoretically, you can connect a maximum load of up to 585 ohms while maintaining this compliance criteria.

    Best Regards,
    Matt

  • 0 in reply to Matthew Sauceda
    Expert 2630 points

    Hi Sauceda-san,

       I appreciate your prompt reviewing.
      Your advice is very helpful!

    Thank you and best regards,
    Tsuyoshi Tokumoto

  • 0 in reply to tsuyoshi tokumoto
    TI__Genius 11750 points

    Howdy Tokumoto-san and Happy New Year!

    I'm glad I could help.  There is one additional change that would improve and benefit your design, and that is to add another 15 ohm resistor at IOUT pin. Currently, in you design, the internal ESD diodes connected to the IOUT pin are connected to the same node as the external rail clamping diodes.  During a transient event, current will flow into both structures, which may potentially weaken the internal ESD structures. To reduce this risk of damage, you can place another 15 ohm resistor in between IOUT and the node of the external rail clamping diodes. This increase in resistance into the IOUT pin will allow more current to flow into the external clamping diodes instead of the internal ESD diodes.

    For more information about this protection circuitry I encourage you to read TIPD216, found at:

    http://www.ti.com/tool/TIPD216

    Best Regards,

    Matt

  • 0 in reply to Matthew Sauceda
    Expert 2630 points

    Happy New Year, Sauceda-san.

     Thank you very much for your rechecking.
     I quite agree with your suggestion.
     I attached the modified schematic.

    Schematic of DAC8775_20180105.xlsx


    Thank you for your continuous support this year.

    Best regards,
    Tsuyoshi Tokumoto