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About output capacitor (CL)and ripple noise of REF5025 & REF5050.

Guru 19475 points
Other Parts Discussed in Thread: REF5050, TINA-TI, REF5010

Please let me know about REF50xx datasheet page-10 "Basic connections".

(please see attach)

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・What is the reason that REF5050 needs CL?

(Is it a measure of noise ripple?)

 

・Is there any graph of "noise ripple vs frequency"?

We want to know the frequency point that a noise become largest.

 

・The capacitor which matched 1μF~50μF & 1Ω~1.5Ω(ESR) is not found.

Please let me know how to choose the capacitor which matched the datasheet's spec.

Or, please let me know a recommended capacitor.

・When ESR is not matched, I will connect in series the resistance on attached-red point.

Is it OK?

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Best regards,

Satoshi

  • Satoshi,

    CL of 1uF to 50uF with ESR of less than 1.5ohm (see tantalum caps) must be used to assure stability of the REF50xx reference voltage.  To minimize the noise ESR of  1ohm to 1.5ohm should be used.  To get the lowest noise, you should connect 1uF cap from TRIM/NR (pin 5) to ground - see below.

      

  • Dear Marec Lis-san

    Thank you for reply.

     

    About CL. is tantalum cap must to use?

    May I use ceramic cap?

    (Foe example, Low ESR Ceramic cap and 1Ω resistor, series connection)

     

    Best regards,

    Satoshi

  • How is the situation?

  • Satoshi,

    Initially it sounded like you could not find 1μF~50μF caps with 1Ω~1.5Ω ESR and thus I suggested tantalum caps.  However, for your REF50xx application you may use either tantalum or ceramic caps as long as their ESR is less than 1.5ohm. You may find tantalum caps with inherent ~1ohm ESR thus avoiding adding discrete resistor but ceramic caps are typically smaller and less expensive so you may also choose this route.  For more info on various types of caps and associated ESR, please see the table below:

  • Dear Marec Lis-san

    Thank you for reply.

    I am sorry for an addition.

    Where is frequency when ripple is the largest?

    (Should a datasheet(figure16~21) be made reference?)

     

    Best regards,

    Satoshi 

  • Satoshi,

    Figures 16 thru 21 in REF50xx PDS show line (power supply change) and load (output current change) transient response as seen at the output of REF50xx. 

    Placing 1uF capacitor on TRIM/NR pin 5 creates a low pass filter with the corner frequency between 10 to 20Hz.  A noise perormance for a combination of CNR and CL output capacitance is shown below.

    I have also attached the Tina-TI schematic so you may simulate the noise spectral density for other cases.

    REF5025 Noise.TSC
  • I'm working with the REF 5010 and have configured it as above. The output, with no load, is only 7 volts.
    I ordered a sample from TI and even purchased from a different vendor and all of them only give me 7 volts.
    My input supply voltage is +15.1 volts. Any ideas???
  • Tim,

    I am not sure what figure you refer to BUT this sounds like the output of your REF5010 oscillates - please verify this with a scope probe.

    It is required to connect 1uF to 50uF output capacitor, CL, with ESR of less than 1.5ohm to make the circuit stable - read below.  

    Also, it is recommended to place a supply bypass capacitor, between GND and VIN, in the range of 1uF to 10uF.

  • Oops, We put the cap on pin 5, not pin 6.
    Sorry for the mix up.

    Thanks
    Tim