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Original question:

REF5050: Voltage output to high

REF5050: Resistor in series with output cap

Dennis McGlumphy
Expert 1390 points
Part Number: REF5050

Dear Trailokya

You said in a prior post that I was exceeding the output capacitor spec (57pf) and overall ESR, (post: REF5050: Voltage output to high, last month).  In the res50xx datasheet, fig. 42, it shows a total of 57uF and a ESR resistor, (see attached image).  Is the information in the data sheet incorrect?  In addition, table 1 page 20, also shows this configuration to reduce noise further as opposed to a single 10uF cap.  Section 12.1 says the ESR should be between 1.0 ohm and 1.5 ohm.  Is there an upper limit to the ESR?

                  

  • 0
    TI__Genius 10951 points

    Hi Dennis 

    Hope you are seeing 5V output .

    • Recommended ESR on for output decoupling capacitor is upto 1.5 ohm. I would not suggest to go beyond that. 
    • Belwo is the recommendation in the layout section (page 21) for output decoupling capacitor (recommendation is upto 50uF)
    • I'd suggest to follow that. 
    • You can put a low leakage capacitors on NR pin to reduce the noise. 

    I will check for inconsistencty in figure 42.  Thanks. 

    Regards

    Trailokya 

  • 0 in reply to Trailokya Rai
    Expert 1390 points

    Dear Trailokya

    Please check with the engineer that is responsible for the component.  I want to make this as quiet as possible but don't want to make it unstable.  Thank you. 

  • 0 in reply to Dennis McGlumphy
    TI__Genius 10951 points

    Hi Dennis 

    Low leakage capacitor on the NR pin will work as a low pass filtr (with 11K ohm resistor) and it will help you to reduce the system noise. You can have output de coupling cap <=50 uF. 

    Regards

    Trailokya