• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 2 answers
  • Subscribers 31 subscribers
  • Views 301 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TMCS1126-Q1: The effect of PSRR on output voltage

Akira Sugimoto
Prodigy 90 points
Part Number: TMCS1126-Q1


Tool/software:

Hello team,

I am estimating the impact of errors on Vout and would like to ask the following question regarding PSRR:

  • When PSRR [A/V] multiplied by device sensitivity, can it be output-referred parameter?
  • Is "Reference Output Voltage PSRR" independent of the Vout deviation stated as "Reference Output Voltage" in the datasheet?
  • Are the Integrated Reference characteristics common between "Vref" which be added to Vout and "VREFout"?
  • Based on the equation "Vout = (Iin × S) + Vref, is my understanding correct that PSRR and Reference Output Voltage PSRR are independent?
  • I understand that the purpose of the "Vref output" is to eliminate offset errors introduced at the system level. Without it, cannot errors caused by power supply fluctuations be canceled out, even if the CPU (ADC) shares a common power line?

Best Regards,

Akira

  • 0
    TI__Mastermind 23895 points

    Hi Akira, 

    Please find answers to your questions below:

    • When PSRR [A/V] multiplied by device sensitivity, can it be output-referred parameter?

    Yes, it can. PSRR is typically handled in the form of an additional offset, and would be treated this way, so it can be output referred or input referred. We have a video located here that walks you through PSRR. 

    • Is "Reference Output Voltage PSRR" independent of the Vout deviation stated as "Reference Output Voltage" in the datasheet?

    Yes and no. The Reference Voltage PSRR here is the amount of rejection on the VREF itself. This VREF voltage will also be present in the output and therefore should be quantified in the output error. We break this value out, however, in case you should want to use this for other means, such as setting the VOC voltage as we show in figure 8-7 of the datasheet.

    • Are the Integrated Reference characteristics common between "Vref" which be added to Vout and "VREFout"?

    I don't quite understand what you are asking here. Can you give me a bit more context here? As I am interpreting this, I believe I have answered this in my above answers. 

    • Based on the equation "Vout = (Iin × S) + Vref, is my understanding correct that PSRR and Reference Output Voltage PSRR are independent?

    Yes, they are independent quantities, but both will be present in the output error as I explain above. One will be due to its coupling on the reference, and the other will be due to its coupling on the output voltage. 

    • I understand that the purpose of the "Vref output" is to eliminate offset errors introduced at the system level. Without it, cannot errors caused by power supply fluctuations be canceled out, even if the CPU (ADC) shares a common power line?

    Yes. If you choose to measure the system single-ended, ie, VOUT referenced to GND, then you can still remove these errors by performing a one point or a two point calibration. A one point calibration would remove all offset errors from your measurement scheme, which would include PSRR errors for a specific temperature operation point. 

  • 0 in reply to Carolus Andrews
    Prodigy 90 points

    Hi Carolus,

    Thank you very much for your detailed explanation.

    Regarding the third question, it's my understanding that the Vref to VREF pin is the same as the Vref be added to the output to VOUT pin because these are from same source according to figure 8-1, Function Block Diagram. In the datasheet, the Integrated Reference characteristics are listed, is it apply to both?

    Best Regards,

    Akira

  • 0 in reply to Akira Sugimoto
    TI__Mastermind 23895 points

    Akira,

    Got it, and yes, your understanding is correct. These characteristics would apply to both the VREF portion of the output, and the VREF pin. Therefore, if you take a measurement with the VREF pin as the reference point, these errors should effectively cancel out. 

  • +1 in reply to Carolus Andrews
    Prodigy 90 points

    Hi Carolus,

    Thank you for all your support. All my questions have been clarified.

    Akira