I have a problem with TL431 voltage reference circuit:
It is irony because C8 was meant to stabilize VREF25.
I tried to use capacitor with higher capacitance (470nF). It did not help.
I tried to use resistor (R10) with lower resistance (330Ω) to increase current (from 1mA to 2mA). It did not help.
3.3V line is this: I use genuine TL431 from NXP.
There's no 139kHz signal in my circuit. Actually I disconnected this voltage reference from the rest of circuitry.
I use SMD components, capacitors and resistors are 0805.