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# TPS54240-Q1: Maximum and minimum duty cycle

Part Number: TPS54240-Q1

Hi all,

I don’t see the marked input/output voltage difference in the data sheet; I want to confirm how to determine that I want to output 3.3V and how many volts should I input at the lowest VIN? The current load is 1.5A, thank you!

• Hi Jerry，

The maximum duty cycle is 100%，you can refer to datasheet 7.3.4 and figure 25 for light load.   Refer to wenbench，3.9V input is totally enough for 3.3V@1.5A. Can 3.9V satisfied  our customer？

BR，

Victor

• Hi Jerry，

As the maximum duty cycle is 100%，the voltage drop depend on the Rdson of HS mosfet and the Res of inductance(estimate 50mΩ). We can estimate from datasheet that the Rdson is around 300mΩ.  The load is 3.3V/1.5A=2.2Ω. So we need at least 3.3V*(2.55/2.2)=3.825V. So 3.8V may be the minimum input which can support 3.3V/1.5A in theory.

BR,

Victor