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Original question:

Clarification on DAC8750 DAC part

DAC8750: DAC8750 Schematic Review

Chitharanjan M1
Intellectual 360 points
Part Number: DAC8750
Other Parts Discussed in Thread: DAC8760EVM

HI Lucas, 

Please find the DAC8750 schematic for 4-20mA current transmitter with 3 and 4 wire configuration. Please review and let me know you feedback if any and clarify below query.

  • May I know what is recommended Voltage that can be provided to AVDD pin for 4-20mA application? is 24V is OK?
  • Since the transformer doesn't support load regulation I would like to use the LDO(24V-15V) on the AVDD_IN  power rail if I can use 15V in AVDD pin for 4-20mA Application. So kindly suggest suitable the part for the same.

Regards,

Chitharanjan M

  • 0
    TI__Expert 4570 points

    Hi Chitharanjan,

    Both 15 V and 24 V AVDD work fine for 4-20 mA output.

    I would make sure your ISET-R Resistor is high precision if you plan on using it instead of your internal Res.
    Other than that, your circuit looks pretty good.

    For 24 - 15 V LDOs, a simple fixed 15 V one is LM341T-15. Let me know if this doesn't work for you.

    Thanks,
    Lucas

  • 0 in reply to Lucas Burnette
    Intellectual 360 points

    Hi Lucas,

    Lucas Burnette said:
    I would make sure your ISET-R Resistor is high precision if you plan on using it instead of your internal Res.

    I have used 15K 1% tolerance resistor, If i want to use internal Resistor what changes to be done? 

    Lucas Burnette said:
    For 24 - 15 V LDOs, a simple fixed 15 V one is LM341T-15. Let me know if this doesn't work for you.

    Thanks for the suggestion and LM341T-15 is through hole part which we are not recommending to use in our design, I would like to have Similar SMD part.

    Regards,

    Chitharanjan M 

  • 0 in reply to Chitharanjan M1
    TI__Expert 4570 points

    Hi Chitharanjan,

    To use the internal RSET, you would need to keep the REXT bit of Control Register as 0. If you are using an external resistor, set the REXT bit to 1.

    For a SMT LDO for 24 V - 15 V, the LM2937 may be suitable. The 15 V version is the LM2937ESX-15/NOPB.

    Thanks,
    Lucas

  • 0 in reply to Lucas Burnette
    Intellectual 360 points

    HI Lucas,

    Thanks for the update.

    May I know what exactly the current consumption of DVDD and AVDD pin of DAC8750 with full load condition? Since in datasheet provided 1mA and 3mA with no load condition.

    Regards,

    Chitharanjan M

  • 0 in reply to Chitharanjan M1
    TI__Expert 4570 points

    Hi Chitharanjan,

    I don't think we have access to the exact board used for originally getting these characteristics, but I can give you an estimated value.

    I used the DAC8760EVM since I already had it set up for testing, which should only be a bit higher than the DAC8750.

    With AVDD ranging from 15 - 24 V, DVDD provided externally 3.3 V, internal VREF, and outputting 20 mA on a 300 ohm load:

    AVDD Supply Current = 23 mA
    DVDD Supply Current = 0.37 mA

    Thanks,
    Lucas