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Capacitor on EN/UV pin of TNY287

Posted by: mahdiabedi on

Hi,
thank you for producing well designed TNY switcher ICs.
I have a question about adding a ceramic cap. on pin number 1 (EN/UV) of TNY287. It is not recommended to use such a cap. in TinySwitch4 family datasheet; But I have seen that in some home appliance switching power supplies, a 1nF or 10nF cap. is used on EN/UV pin.
Also testing a 15w PSU (with two outputs 12V, 0.9A and 5V, 0.4A) with and without 1nF cap. , I've seen that using this cap. on pin1, reduces amount of noise on both outputs.
What is your suggestion about using this cap? Does it cause any problem in the functionality of PSU?
If it is recommended which amount of this cap is suitable? 10nF , 1nF or 100pF?
Regards,

Comments

Submitted by PI-Kryten on 06/29/2020

Hi,
Thank you for considering Power Integrations for your solution.
We do not recommend a capacitor on EN/UV pin.
The fact that this design needs a capacitor at the EN/UV pin for better performance is an indication of something not right in the layout.

Please ensure that the optocoupler is connected directly to the EN/UV pin. Also ensure that the tarce from the emmiter of the optocoupler to the source pin is not shared with anyother component such as the input capacitor for example.

Best Regards,
PI-Kryten