TL1431: unstable output (oscillation)

Daisuke Higa

Part Number: TL1431

Hi support team.

My customer has an oscillation problem in the TL1431 circuit.

When the ESR of the output capacitor is set to 100 m ohm or less, it oscillates and stabilizes at 1 ohm or more and 3 ohm or less.
They have confirmed that it oscillates again when the ESR is set to 4 ohms or more.
Could you give me some data or resources on ESR stability conditions? (Is it somewhere just because we can't find it?)
Also, I would like you to check our schematic, is it possible?
If yes, it is not allowed to be open to the public because of the customer's circuit diagram, so can you send me a private message?

Let me know if you have any question.

Thank you for your cooperation.

Best regards,
Higa

over 4 years ago

0 Marcoo Z over 4 years ago

TI__Mastermind 19580 points

Hi Higa,

The TL1431 is unstable with certain capacitors when the ESR is low. This is shown in the datasheet in figure 12.

Check if the output cap is around 0.1uf - 1uF and just move away from that if possible.

Is this what is occurring?

0 Daisuke Higa over 4 years ago in reply to Marcoo Z

Genius 4315 points

Hi Marcoo-san

Thank you for your prompt reply.

The ESR conditions are not in Fig12.
My customer would like to know the condition of ESR.

In particular, why does it oscillate above 4 ohms?

Our circuit is below.

Best regards,

Higa

0 Marcoo Z over 4 years ago in reply to Daisuke Higa

TI__Mastermind 19580 points

Hi Higa,

Increasing the 4 Ohm resistor will isolate the 22uF cap from the TL1431 allowing the 0.1uF cap to have a larger effect on the stability. 0.1uF cap is a unstable and it is highly recommended to change that value.

Figure 12 is designed for low ESR capacitors like ceramic capacitors. We do not have a ESR cutoff but the more ESR the capacitor has the more stable the device is.

0 Daisuke Higa over 4 years ago in reply to Marcoo Z

Genius 4315 points

Hi Marcoo-san

Thank you for your advise.

I understand.

If VKA is 3.1V, should I use case B in FIG12?

0 Marcoo Z over 4 years ago in reply to Daisuke Higa

TI__Mastermind 19580 points

Hi Daisuke,

I would choose A to be more conservative. The reasoning is that the line shows 0 degree phase margin, most designs need some margin away from this line.

0 Daisuke Higa over 4 years ago in reply to Marcoo Z

Genius 4315 points

Hi Marcoo-san

Thank you for your support.

I understood.

Best regards,

HIga

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TL1431: unstable output (oscillation)