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TL431: Resistors specs for TL431

Andriy Orlyk
Prodigy 50 points
Part Number: TL431

Hello.

Might I ask what resistors power ratings are required for shunt regulator in Fig. 27 of the datasheet?

The power amp board I'm using TL431 which is set for 15V out has some oscillation at a start, so called "motorboating". Could the source of instability be TL431 if maximum current out reached? To suppress this instability should I use 0.22uF between cathode and anode?

The maximum current for TL431 at 15V out is only 20mA?

Thanks,

Andriy.

  • 0
    TI__Mastermind 19370 points
    Hi Andriy,

    The power rating of the resistors I typically use are 1/8W just because I usually use a breadboard. As long as the resistors are able to supply the 4uA into the REF pin, you should be good.

    It sounds like the source of the problems could be instability or temperature related. I would looking figure 16 and look at what capacitances to avoid. Keep in mind that you would want some margin away from the boundary because this is a typical graph that does not consider corner cases or temperatures. In your case, 0.22uF is unstable.

    If it is not unstable, check the temperature of the device. 15V at 20mA is 0.3W through a very small device. Looking at its RthetaJA in section 7.3, the device can experience a high temperature increase and if this violates the operating temperature it could oscillate. Temperature also limits the maximum current depending on package and operating conditions. So the max current is system dependent.

    If you need to use high currents at high voltages, I would use something close to fig 31 or fig 34 because the majority of the current will not go through the device.

    -Marcoo


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