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DAC8811: DAC output circuit

Part Number: DAC8811

Dear Team, 

I want to evaluate the output circuit of DAC8811 as attached.

Can anyone suggest how to simulate the circuit in Tina TI.

 I have created the attached circuit. But it is not giving expected output.

My requirement is to swing the output from -5 to +5V.

please also suggest the OP Amp and supply requirements.

DAC8811_test.TSC

Regards

Rohit

  • ,

    I am attaching the simulation circuit for the same.

    In order to get bipolar output from -5V to +5V , you can use methods.

    1. Use Ref  = 2.5V and use the above circuit and additional gain stage ( having one more op amp or modify the second stage)

    2. Use Ref  = 5V and above circuit will give you -5V to +5V

    Please see the attached simulation circuit for better understanding. In the circuit, 0mA corresponds to code 0 and 1mA corresponds to full code.

    when current  = 0mA, output will be at-5V and when current  = 1mA, output goes to 5V providing you with bipolar -5V to +5V.

    Op amps can be the one above  and supply has to be +/-6.5V min

    Hope this clarifies your query. Let me know if you need more help.

    5773.DAC8811_test.TSC

    Regards,

    AK

  • Hi AK,

    Thank you for the updated circuit.

    I have following queries:

    1) I read somewhere RFB resistor R5=10K for DAC8811 but you have used 5K, do you have any documentation or reference for this resistor value?

    2)You said full code will give 1mA and code 0 give 0mA current, I want to understand this calculation.

    3) In reference picture  there is C2 , is it necessary?

    Regards,

    Rohit 

  • Hi,

    Actual value of feedback is 5K.

    You can change these value to reflect the actual resistance. As far as current is concerned, its function of reference voltage itself.

    For 10V reference, full scale current will be 2mA ( Datasheet) and this will scale according to code and reference voltage.

    So for 2.5V reference current will be 500uA ( 0.5mA) and I to V converter stage full scale will be 10K *0.5mA = 5V.

    I am attaching the simulation circuit with Vref  = 2.5V and Feedback as 10K for checking purpose

    6562.DAC8811_test.TSC

    Regards,

    AK

  • Hi,

    Thank you for the explanation

    If I want -+5V swing then My Vref will be 5V

    Then current will be 1mA. and I to V converter stage full scale will be 10K*1mA=10V.

    Please check the attached circuit I am not getting +-5V at output of 2nd stage.0285.DAC8811_test - autosave 20-10-13 19_18.TSC

  • Hi,

    For 5V reference for DAC, your I to V stage will be at -10V at full code, you need to convert that to +5V.

    To do that you need to feed Vref/2 to inverting terminal and change according to the circuit below

  • Hi,

    I agree with you, by doing these changes I can have +-5V swing at output.

    But what is the meaning of this circuit? How they are able to generate output swing equal to Vref value with these values.

    Regards,

    Rohit

  • Hi Rohit,

    I checked in design docs and seems RFB value is 5K only. So based on this, the above circuit is true.  Generally the value of RFB is not always explicitly listed in the MDAC’s datasheet but it is typically equal to the input impedance of the reference pin. So for DAC8811 its 5K

    I am attaching modified circuit in which RFB is 5K and it works as expected. My apologies for the confusion here.

    Regards,

    AK

  • Hi,

    Thank you.

    If it is 5K then my query is resolved.

    Regards,

    Rohit