TL431LI: CL for stable operation

Takashi Onawa

Genius 13200 points

Part Number: TL431LI

Hi Team,

My customer is considering to use TL431LI to generate 3.3V power supply for RTC which requires less than 10uA.

I was asked to review their following schematic though, could you help that?

They mind CL is enough to get stable operation with the circuit below especially.

According to the datasheet, more than 2uF is needed for very low IKA condition, I think they should put much amount CL to prevent oscillation.

So could you tell me how much CL is recommended for safe operation under VKA=3.3V condition when DC bias is also taken into account?

Regards,

Takashi Onawa

over 2 years ago

+1 Ben C over 2 years ago

TI__Mastermind 27495 points

Hi Takashi-san,

Based on their schematic, the VKA for the TL431LI is around 3V. Therefore, looking at the stability curves, the region of operation is between the blue and black region. Having 1uF capacitance on the output is a little close on the edge of instability (not much margin). Capacitors also have voltage derating properties. Your suggestion is very valid and I would suggest that the customer use a 2.2uF capacitor.

Ben

0 Takashi Onawa over 2 years ago in reply to Ben C

TI__Genius 13200 points

Hi Ben-san,

Thanks, I understood. I recommend to put more cap as CL just in case.

Regards,

Takashi Onawa

0 Ben C over 2 years ago in reply to Takashi Onawa

TI__Mastermind 27495 points

Hi Takashi-san,

Glad to be of help. Good luck to you!

Ben

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TL431LI: CL for stable operation