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TPS54561-Q1: About SW node voltage

Part Number: TPS54561-Q1

Dear Sir/Madam:

I need some clarification on TPS54561-Q1. I am using it for converting 50V to 5V. As specified in the datasheet, the Sw node voltage should not exceed -0.6V.

Since my catch diode forward voltage is 0.582V@8A, and I am getting -0.9V steadily @ 1A load current during OFF time.What I can do to bring the negative voltage less than -0.6V.

My design gets almost over.I don not want to change IC.


Best Regards,


  • The -0.6V absmax spec on the SW node is a DC spec. I believe when you say your SW node voltage is -0.9V referring to ringing spikes at the falling edge of the SW waveform. It does not violent the DC spec. Also, the observed ringing magnitude may change with probing of the node. Make sure the ground loop of your probe is minimized. Layout of the board also affects ringing magnitude. Please double check your layout with datasheet layout recommendations.

    BTW, 0.582V drop@8A equals 4.6W of power loss if continuous 8A going through this diode. If you run full load 5A with 50V input and 5V output, approximately 90%*5A*0.582V=2.6W of power lost on this diode due to the drop. There are other switching loss etc. on top of this. A lower drop diode is recommended if you want to improve heavy load efficiency and reduce power loss.