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LNK3206G explodes

Posted by: VEEK1221 on

Hello,

My team designed an AC/DC power supply that has 220V 50hz input and has 24V and a maximum of 0.1A output. The board's only purpose is to generate DC using LNK3206. Unfortunately, the IC exploded when we first powered on the board.
It had no load, only a burden resistor of 5.49kohm. Thankfully no one was injured. Attached is a picture of the exploded IC.

Can someone please tell me what might be the cause of the explosion? The IC has so many built in protections (short circuit, output overload and so much more). How come it exploded?

Attached is the schematic of the circuit.

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schem.png 65.25 KB

Comments

Submitted by VEEK1221 on 02/05/2019

Hello,
Please we need help from you to see what is wrong. Project has stopped because of this. Please reply as soon as possible.
Waiting to hear from you.
Thank you.

Submitted by PI-SevenOfNine on 02/07/2019

Hi VEEK1221,

Thank you for using PI product on your design. We supposed that the IC blows up when you power-up at 220V, 50Hz? Based from your schematic, you put parallel capacitors across the feedback upper resistor R17. The capacitor value were also very large. Large value is not recommended as this might affect the soft start. Also you were using the largest size of the LNK-TN2 family (LNK3206), which has a large peak current limit. Based from the datasheet the peak current limit ranges from 408mA to 520mA. And your chosen inductor (L2) is rated 420mA. Even with no load condition, the inductor will see this peak current. Its possible that the current in the inductor is also in saturation that might damage the device. Please choose a higher rated inductor and try removing C24 and C25. Thank you.

Best Regards,
PI-SevenofNine

Submitted by VEEK1221 on 02/07/2019

Hello PI-SevenofNine,

Thank you for your response.

Yes it is true that IC blows up when i power it up at 220V 50Hz.

I followed the guidelines provided in application note AN70 and PI-expert about the value of the soft start capacitor. AN70 recommends a value between 0.47uF to 47uF for voltage outputs more than 12V (my application has 24V output). On the other hand PI-expert recommends 1-100uF of capacitor on soft start. I used a value of 2uF for this capacitor. On the other hand, the inductor that i am using has a saturation current of 0.65A making it suitable for such application.

Any help would be really appreciated as we are in the middle of the production stage and would like to know how to proceed.

Thank you.

Submitted by PI-SevenOfNine on 02/19/2019

Hi VEEk1221,

Did you try to reduce the capacitor value? This capacitor might affect the stability of the system. Can you screenshot your PCB layout? Thank you.

Best Regards,
PI-SevenofNine