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Original question:

DAC3152 output level low

DAC3152: ANALOG CURRENT OUTPUTS

Naizeng Wang
Expert 4660 points
Part Number: DAC3152
Other Parts Discussed in Thread: THS3217

Hi team,

Customer wants to use it to output square waveforms whose range is from 0 to 2.5V and frequency is adjustable. I have several questions about DAC3152's output. 

  • According to page19 of datasheet, we need to use transformer to convert differencial signal to single end signal, can we use OPA to achieve it? Customer doesn't want to place a transformer here. Could you please suggest the mature OPA circuit?

  • And also in this page, Applying a 20-mA full-scale output current leads to a 0.5-Vpp output for a 1:1 transformer and a 1-Vpp output for a 4:1 transformer. Could you please share the detailed calculation process? 

Br,

Nison

  • 0
    TI__Expert 4660 points

    Another question: customer wants to output constant voltage signal using another DAC channel. The concern is that if we use the transformer, will it saturate due to constant DC signal? 

  • 0 in reply to Naizeng Wang
    TI__Mastermind 20845 points

    Hi Nison,

    A transformer is used if the application is AC coupled. What you have described here from the customer is DC coupling. Not just any op amp will work for this. A differential to single ended amplifier designed for use as a DAC output amplifier is suggested. For example, please refer customer to look at THS3217. Please find resources about DC coupling DAC output here: https://www.ti.com/lit/ug/tiduc44/tiduc44.pdf

    The max Vpp output is calculated as twice of what each of the individual IOUTP and IOUTN drive at max output current, in this case 20mA. In other words, the differential impedance between IOUTP and IOUTN should first be calculated and then multiply by the current swing.

    In the case of the 1:1 figure (Figure 41), the differential impedance is 50Ω between IOUTP and IOUTN. 20mA * 50Ω = 1Vpp. 

    In the case of the 4:1 figure (Figure 42), the differential impedance is 100Ω between IOUTP and IOUTN. 20mA * 100Ω = 2Vpp.

    Regards, Chase

  • 0 in reply to Chase W
    TI__Mastermind 20845 points

    As you can see here at the end, if the differential impedance is calculated between IOUTP and IOUTN for the 4:1 case, the equivalent resistance is 100Ω and therefore the output Vpp is 20mA * 100Ω = 2Vpp.

    Regards, Chase