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Internal open circuit in TOP-261YN

Posted by: patquilter on

We are using the TOP261YN in a non-PFC, universal voltage application, mostly at 120Vac (169Vdc nom) to get the maximum available power (approx 250W). I have used various TOP-Switch parts over the years with good results. The TOP261YN has two special design considerations that we are observing: 1) operates at 66kHz only and 2) special isolated connection from pins X and GXC to 0.1uF capacitor connected to input C,, providing a specific internal ground path to prevent problems at high current. According to the app note, these external pins are not to be separately grounded to Source. 99% of parts are good but we have now had had several parts which passed initial testing, but went bad later, wherein the internal ground connection between X-GXD and S has gone open, resulting in non-operation. 

 

Our big question is what is causing this internal connection to open? Would it be legal to Kelvin connect these pins externally to the Source pin?

 

A second problem is that the 66kHz part reduces to 16kHz at low power, which is audible to some customers. Is there a way to keep the frequency above 20kHz? The spec sheet states 33kHz minimum. 

 

Please help!

 

Pat Quilter, Quilter Labs.  

 

 

Comments

Submitted by PI-Terry on 12/16/2013

Hi,

 

The G pin and source pin is internal connected, they should not be connected together externally. Would you please attached the layout and schematic, then I can see if there is a violation of the design rule?

 

Considering the minimum switching frequency, yes, the minimum switching frequency will be clamped to about 30kHz. But if the power supply is working in Milti Cycle Mode, then the MOSFET will switch on for 4 or 5 cycles with 30kHz and then stay off until the control pin current falls below ic(off). Would you please send me the drain voltage waveform with the 16kHz switching frequency that you mentioned? I would like to have a confirmation.

Submitted by PI-Terry on 12/16/2013

Hi,

 

The G pin and source pin is internal connected, they should not be connected together externally. Would you please attached the layout and schematic, then I can see if there is a violation of the design rule?

 

Considering the minimum switching frequency, yes, the minimum switching frequency will be clamped to about 30kHz. But if the power supply is working in Milti Cycle Mode, then the MOSFET will switch on for 4 or 5 cycles with 30kHz and then stay off until the control pin current falls below ic(off). Would you please send me the drain voltage waveform with the 16kHz switching frequency that you mentioned? I would like to have a confirmation.