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OPA2277: Input current required for simulation

LAKSHMI PRIYA C
Prodigy 250 points
Part Number: OPA2277
Other Parts Discussed in Thread: DAC8820, OPA277

Hi Team,

 I am using DAC8820ICDBR in my design. We are using a bipolar DAC with +/-10V. Being a current DAC, a transimpedance amplifier OPA2277UA has been used to provide equivalent voltage. What is the equivalent current output, a DAC can provide as an input to OPA2277 for getting +10V and -10V? Below is the schematic circuit connection and transimpedance amplifier circuit connection for simulation. Please help me on setting the input current for transimpedance amplifier.

  • 0
    TI__Guru 54106 points

    Hello Lakshmi,

    On the DAC8820 datasheet recommended circuit, the op-amp output connects directly to the RFB and ROFS pins of the DAC. The current flows between the RFB/ROFS DAC pins and the op-amp output. The DAC IOUT pin connects to the op-amp inverting terminal.   Please note, there is a very small input bias current or virtually no current flow into the inverting input of the amplifier. 

    The OPA277 TINA simulation shown above is not correct. It connects the current source to the inverting input of the op-amp.  Keep in mind, the inputs of the op-amp are high impedance and only a small input bias current flows into the amplifier inverting input. The RFB/ROFS DAC current flows to the op-amp output.

    The DAC8820 current into the (I/V) precision amplifier is dependent on the digital code, and the reference voltage. Your simulation needs to include the equivalent R-2R DAC ladder and DAC circuit model. Please find the DAC8820 TINA model on the link below that will be useful on your simulations. 

    If you have additional questions related to the DAC8820 or DAC8820 model simulations please address your query on the Data Converters Forum.

    Thank you and Regards,

    Luis

    DAC8820 SIMULATION MODEL

    DAC8820 TINA-TI Reference Design