Hi Team,
I am pushing customer to replace Nexperia's TL431BQDBZR. we found that there has difference on Stability Boundary Conditions.
TI:
Nexperia: https://assets.nexperia.com/documents/data-sheet/TL431_FAM.pdf
Could you let me know if TI can directly replace Nexperia? whethere there has osililation issue?
there are typical below applicaiton design:
1) TL431 as flyback feedback reference.
2) TL431 to build a LDO.
thanks a lot.
Best regards,
Yang
Hi Yang,
Thanks for your question!
I first wanted to clarify, are the schematic screenshots flipped? The first image is the LDO application and the second one is for flyback converter feedback. Is this correct?
As shown in the datasheet, the oscillation occurs in relation to the load capacitor CL (shown below):
For the flyback converter feedback schematic, there is no load capacitor (a capacitor between cathode and anode) so I do not see any issue with a direct swap.
For the LDO schematic, it could be possible that there is some parasitic capacitance from Q58 and D141 that connects to C827 and the other capacitor in parallel to C827, but I do not foresee this to cause any problems since these parasitic capacitances should be very small in a series capacitance configuration. As a result, the effective load capacitance would be in the stable region of TI's TL431.
Overall, I do not see any stability concerns in these applications for swapping from Nexperia's TL431 to TI's.
If stability is still a concern, one solution I would also recommend would be to utilize TI's new TLA431 which is an improved, all-capacitor stable version of TL431. Please see the (very simple) stability curve below:
There will be no stability concerns with this device: https://www.ti.com/product/TLA431
I hope this helps!
Best Regards,
Andrew Li
