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Original question:

DAC5311-Q1: DAC5311-Q1:

DAC088S085: voltage accuracy from the DAC and ripple from converter TPS62902

Sonom Olonbayar
Prodigy 145 points
Part Number: DAC088S085
Other Parts Discussed in Thread: TPS62902, , TPS62912, TPS62913, ADC12DJ5200RF

Dear TI support,

The DAC I want to use requires to apply1 V reference voltage externally. Therefore its accuracy is defined as follows 

V = Vref * (D/256)=1V*(D/256): 

This then offers a voltage resolution of 4 mV. I am thinking to use voltage regulator or DC/DC converter TPS62902 to get 1 V reference. I did PSPICE simulation for a converter similar to it as recommended. However I can not read the voltage at mV accuracy. With that regard I would like to clarify if such accuracy can be achieved? How much ripple can we get from the above converter for 1 V output voltage? If it can stay below 4 mV so that the DAC's accuracy is possibe? It will be great to receive any recommendation and comments on that. 

With the best Olonbayar

  • 0
    TI__Mastermind 25433 points

    Hi Olonbayar,

    Your post has been placed in the DAC forum. I am going to move this to the proper team to answer your questions about the TPS62902. I will stay subscribed to this thread in case you have any additional questions about the DAC088S085.

    Best,

    Katlynne Jones

  • 0
    TI__Mastermind 21755 points

    Hi Olonbayar,

    The 4mV requirement is tight for the TPS62902. However, you can take a look at the TPS62912 (2A) and TPS62913 (3A) which can achieve really low ripple and are well suited for your application. Please let us know if you have further questions on these devices.

    Thanks,

    Amod

  • 0 in reply to Katlynne Jones
    Prodigy 145 points

    Hi Katlynne, 

    Thanks for your quick response. How much the reference voltage should be ripple free  for the DAC mentioned above? 

    I mean the reference voltage 1V. Is there requirement to the accuracy of this reference? 

    Thanks Olonbayar 

  • +1 in reply to Sonom Olonbayar
    TI__Mastermind 25433 points

    Hi Olonbayar ,

    There is no accuracy requirement. But ripple on the reference input will translate directly to ripple on the DAC outputs. This will depend on your design requirements. You are correct that the reference should have less than 4mV of ripple to get the full 8-bit resolution of the DAC. 

    Best,

    Katlynne Jones 

  • 0 in reply to Katlynne Jones
    Prodigy 145 points

    Hi Katlynne, 

    thanks for your replies. I have an another enquiry. I was looking at the evaluation board for this DAC. There are resistors and capacitors connected to all outputs of it. I think I also should do that. Do they affect the voltage level at the outputs? It will be great if you comment on that. 

    With the best Olonbayar

                  

  • 0 in reply to Amod Vaze
    Prodigy 145 points

    Hi Amod,

    thanks for your replies. The converter you suggested looks good. I have few inquiries. 

    Can I tie several load to the TPS62912 output as it was shown in Fig-8-81 of the TPS62902 I was planning to use before? 

     There are some capacitors shown as 3xCin=3x22uF. Do they imply to connect three Cin capacitors in parallel? 

    Thanks in advance

    Olonbayar 

  • 0 in reply to Sonom Olonbayar
    TI__Mastermind 25433 points

    Hi Olonbayar,

    The resistors and capacitors are provided for evaluation purposes on the EVM. Jumpers can be placed on header J8 to connect or disconnect the test loads from the DAC output. I assume you application will at least have some sort of resistive load. If you were using the EVM for evaluation you'd add a similar restive load to test how the DAC output will behave.

    What are you using the DAC output for? You likely don't need to add any extra resistance or capacitance at the output. 

    Best,

    Katlynne Jones 

  • 0 in reply to Katlynne Jones
    TI__Expert 4600 points

    Hello,

    You can tie multiple rails to a single TPS62913 output.  This was done in the ADC12DJ5200RF example here:Powering Sensitive Noise ADC Designs with the TPS62913 Low-Noise Buck Converter

    The key is to make sure that the highest load is the one where you place the remote FB sense point.  You also want to have a small cap at each load as shown in the schematic for that design.