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Not getting current out out more than 20mA in DAC7760 EVM

sagar salunkhe
Intellectual 445 points

Other Parts Discussed in Thread: DAC8760EVM

Hi ,

       I have purchased EVM7760 kit . I have configured 4 to 20mA output in the kit from DAC8760EVM software. I set DAC value to 0xFFF0 then i measured current i got current out to 19.83 mA.

    Hardware setting:

    AVDD= +12 v

    AVSS= -11V

   DVDD= 5.09V

   Ref= on board ref. (4.96 V)

  IC on the board: 7760

    Then i configured calibration enable button and set gain calibration to 0xFFF0 i found that still i am getting 19.83mA current . I am unable to increase current more than 19.83 mA.

  note: i  increased gain from 0x00 to 0xFFFF , i found that above   0x7DC8 value current output is 19.83mA fix not increasing with gain value.

   Why it is not giving current more than 19.83mA??? I want 20 mA current in my application.

Thanks & regards,

Sagar

  • 0
    TI__Genius 10615 points

    Hi Sagar,

    I need to ask you a few questions in order to help you debug this problem:

    • Can you send me a picture of your setup? I want to verify the setup of all the jumpers.
    • What load are you using?
    • Can you measure the voltage at the Iout pin?

  • 0 in reply to Eugenio Mejia
    Intellectual 445 points

    Hello  Eugenio Mejia,

    Can you send me a picture of your setup? I want to verify the setup of all the jumper :  

    I wil tell you position of all jumper

     Jp9 : conected

     jp7 : 1-2 connected

    jp3 connected

    jp1: open

    jp2:  2-3 connected

    jp6: open

    jp5 : open

    jp8: connected

     

     

    What load are you using?

    I am not using any load for current measurement just using Digital multimeter. (DMM)

    But with help of on board 300 ohm resistor i measured Volt and calculated current still i am getting 19.83 mA current not 20mA

    Can you measure the voltage at the Iout pin?

    yes i measured voltage i got 5.95 V out put across 300ohm resistor.

    Regards,

    Sagar Salunkhe

  • 0 in reply to sagar salunkhe
    Intellectual 445 points

    Hello  Eugenio Mejia,

        I have enabled Control Register 's DB14 bit  (OVR) but still no use.Please suggest your valuable suggestions.

    Regards,

    Sagar Salunkhe

  • 0 in reply to Eugenio Mejia
    Intellectual 445 points
    No one has idea about this or my board is faulty should i ask for another board from TI?
  • 0
    TI__Genius 10615 points

    Hi Sagar,

    sagar salunkhe said:
    Ref= on board ref. (4.96 V)

    This might be the source of your issues. A reference of 4.96 V would give your an ideal output range of 19.84 mA, combined with a minor TUE error you could easily hit the 19.83 mA.

    The internal reference of the part should not be less than 4.995 V, are you loading it by any chance?

    However, keep in mind that the devices has a max TUE of 0.8% at room temp, which even with a perfect reference will give you 19.84 mA. Max specs are highly unlikely, but possible. The 0.2 % typical TUE will give you a 19.96 mA output.

    Is it okay to contact you to your E2E registered email in order to get your contact info and send you another EVM?
    Also, do you think its possible for you to send me a picture of the device markings so I can check the lot that this device came from?

    sagar salunkhe said:
    note: i  increased gain from 0x00 to 0xFFFF , i found that above   0x7DC8 value current output is 19.83mA fix not increasing with gain value.

    The gain register is simply for digital calibration. This means that the transfer function can be gained/offset up or down, but only without the original max and min outputs.