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DAC3162: How to achieve 0V-1V output?

Ian Biagioni
Prodigy 30 points
Part Number: DAC3162
Other Parts Discussed in Thread: , THS3217, OPA694

Dear community,

I'm designing a board and i wanted to use the DAC3162 to generate a single ended output between 0V and 1V to feed into a 50Ohm load. I have never worked with DAC so I'm not sure on how to achieve this correctly. 

I'm taking the DAC3162 datasheet and DAC3162EVM schematics as reference. I get that I need to use a 4:1 transformer to achieve a 1Vpp but I have doubts on how to change the CM level.

Just connecting the central tap of the secondary to a 0.5V reference do the trick? Is there an already working solution to this problem? 

Thank you for any help,

Ian

  • 0
    TI__Guru* 91947 points

    Ian,

    Just follow Figure 42 of the data sheet to create a 1Vpp output. Since the output is AC coupled by using the transformer, you do not have to worry about the CM level. You will need the part to sink the maximum amount of current, which is 20mA. For this, you will need the Rbias resistor to be set to 960 Ohms. If you use the same resistor values as shown in Figure 42 and the 960 Ohm Rbias resistor, you should be fine. Make sure the IOUTP/N pins and the transformer center tap are all connected to +3.3V per Figure 42. To reduce possible noise, I would suggest adding a 0.1uF cap between the transformer center tap and GND as shown in the EVM schematic.

    Regards,

    Jim   

  • 0 in reply to jim s
    Prodigy 30 points

    Hi Jim,

    thank you for your answer, I understood that I was confused about my problem.

    I need the signal to be DC coupled so that I can generate an arbitrary waveform between 0V and 1V. Thanks to you I understand I need to use one or more OPAMP to condition the DAC signal. Is there a reference to do this? I have found something but all referes to DAC with output complience around 0V. 

    At the moment the only solution i'm thinking of is to use a differential-to-differential amplifier and then a differential-to-single ended one. Are there better solutions?

  • 0 in reply to Ian Biagioni
    TI__Mastermind 18185 points

    Hi Ian,

    You unfortunately cannot just connect a 500mV reference at the secondary center tap for this. Passive options are inherently AC coupled devices. In order to DC couple, you will have to use an active part. Please see the attached document as a reference.

    Regards

  • 0 in reply to Chase W
    Prodigy 30 points

    Hi Chase,

    thank you for your answer and the reference. I am evaluating two options:

    - I have seen the THS3217 and somehow managed to simulate my desired output on TINA. But I have seen at page 30 of its datasheet that "This DAC-to-THS3217 configuration requires at least a 300-mV dc level shift with half the tail current in each side, implying a 30-Ω load impedance to the supply on each side of the 20-mA reference current.". But this voltage swing is outside of the output compliance level for DAC3162. Mounting a 25ohm resistor to Vcc, is a voltage divider on both + and - side a proper solution to adapt the voltage level? Considering that the voltage divider will move a bit the voltage at DAC output.

    - The circuit proposed in the document "Interfacing Op Amps to High-Speed DACs" gives an output voltage between +V and -V. Is biasing the Op Amp output connecting a voltage reference to the non inverting input a proper solution? 

  • 0 in reply to Ian Biagioni
    TI__Mastermind 18185 points

    Ian,

    Can you provide the TINA file for this solution? I am having a hard time following what you are asking on the last part of the first paragraph.

    Thanks

  • 0 in reply to Chase W
    Prodigy 30 points

    Hi Chase,

    you are right, I have not been very clear with my explanation.

    DAC_Isink_THS3217_VD.TSC

    Anyway I have seen that I should chose high value resistor for the divider but this degrade the frequency response of the system.

    Guess the only option is to follow "Interfacing Op Amps to High-Speed DACs" guidelines and connect a bias voltage on the non inverting input. 

  • 0 in reply to Ian Biagioni
    TI__Expert 7875 points

    Hi Ian, 

    For the THS3217 you can choose any resistor values you would like on the DAC output interface as long as the minimum and maximum voltages delivered to the THS2317 inputs stay within their compliance range. The inputs to the THS3217 are high impedance so they will work with most resistor values. 

    Regards, 

    Jacob 

  • 0
    Prodigy 30 points

    Thank you all for your support! I have a much better understanding on the topic now. 

    I've tried different configurations both with the THS3217 or an op-amp. The most satisfying one (at least considering the simulations) is the following one, using OPA694. I'm leaving it for reference. 

    DAC_Isink_OPA694_ok.TSC