TPS54821: Dead Time ; Efficiency calculation including Bottom FET switching and

Stuart Currie

Part Number: TPS54821
Other Parts Discussed in Thread: TPS54824, TPS549A20

I would like to roughly budget the power lost in the bottom FET body diode in the TPS54821 and TPS54824 and TPS549A20.

What are approximate values for the inputs to this equation for low side FET for these devices. Nothing is specified or charted.

Just first order values are fine.

Vout is 0.8V. Does this low voltage impact the loss in the bottom FET\diode as drain to source is low?

0 Neal Zhang over 8 years ago

Hi Stuart, can you share with me your output current and input voltage?

0 Neal Zhang over 8 years ago

For your reference, the typical dead time is 18 ns and voltage drop the diode is 0.7 V. So in your equation, VF=0.7, tDLYUpLo=tDLYLoUp=18n.

0 Stuart Currie over 8 years ago in reply to Neal Zhang

12V in ; 7.5A out

0 Neal Zhang over 8 years ago in reply to Stuart Currie

It should be OK. Did you see some abnormal phenomena?

0 Neal Zhang over 8 years ago in reply to Stuart Currie

Because of the minimum on time, in your spec the switching frequency should be designed below 384kHz

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