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TL431: The measurement value of Vref

Y.Ottey
Mastermind 6145 points
Part Number: TL431

Dear all,

Could you give me some advice about the following content?

Our customer ask the cause of phenomena like below.

Our customer measure value of Vref with the circuit below

※Rsup=910Ω, R1=130Ω,R2=120Ω, C1=4700pF, CL=1μF Vsup=＋24V

measurement value : Vref=2.457V, 2.454V, 2.460V, 2.452V、2.453V

specification value： Vref=2.483V～2.507V

As understood from above value, measurement value is out of specification value's range.

So, I would like to advice about cause of above content.

It would be great if you could let me know your thoughts this cause.

Best Regards,

Y.Ottey

  • 0
    TI__Genius 9375 points
    Y.Ottey,

    You are correct, the values you are seeing are out of spec. I was wondering if you could share some more information with me so I can help you further. Do you have any scope shots visualizing what you are seeing at the output here? I'm curious to see the waveform.

    My first thought is that it is potentially your load capacitor value that needs to be adjusted. Please see here for further info on oscillation due to teh load capacitor: www.ti.com/.../slva482a.pdf

    Thanks,
    Abhinav.
  • 0 in reply to Abhinav.Sharma
    Mastermind 6145 points
    Hi, sharma.

    Thank you for your reply.

    I heard from the customer that the values of resistors and capacitors in the circuit are changed as follows.
    Rsup=910Ω→910Ω
    R1=130Ω→13kΩ
    R2=120Ω→12kΩ
    C1=4700pF→OPEN
    CL=1μF→10μF

    Are there any problems with the value as above?

    Regards,
    Y.Ottey
  • 0 in reply to Y.Ottey
    TI__Genius 9375 points
    Y.Ottey,

    My next question was going to be regarding the C1 capacitor, and it seems they've decided to open it here, so that should be fine. The other values seem okay as well, but our datasheet example uses 100 nF for CL. If you look at section 10.2.2 of the TL431 datasheet, you can see a shunt regulator example with this setup that should help you design this circuit without any problems.

    In addition, I want to suggest that you take a look at the TL431LI; it is a pin-to-pin alternative to the TL431 and offers better stability, lower temp drift, and higher accuracy.

    Thanks,
    Abhinav.