TPS543C20A: How the duty is determined in Webench report

Ella KIM

Part Number: TPS543C20A
Other Parts Discussed in Thread: TPS543C20

Hi Team,

I have two questions while running TPS543C20A Webench simulation. Basic operating condition is as below and I also attach the Webench reports.

VinMin = 10.8V
VinMax = 13.2V
Vout = 0.85V
Vout Sch = 0.85V
Iout = 40.0A

Fsw = 500kHz

1. How is the duty cycle determined in the report? I run it with Ta = 25 degC and with Ta = 55 degC. And duty is 7.182% and 7.301% each. I expected the duty would be 6.44~7.87% (0.85V/13.2V~0.85V/10.8V).

2. Why the duty is different in the two reports - only difference in setup is Ta 25 degC vs 55 degC.

3. I basically want to see the TPS543C20's Tj performance along with Vout and Iout change (non-A version). Do you expect the Tj would be same or similar to TPS543C20A simulation result?

WBDesign58_1.pdf WBDesign58_2.pdf

Thank you!

over 3 years ago

+1 Tahar Allag over 3 years ago

TI__Mastermind 32400 points

Ella KIM

Hello Ella,

Answer to 1st and 2nd Questions:

I found these applications note and FAQ can be a good starting point to understand how the D can be affected by other parameters to answer your 1^st and 2^nd questions. Please note that the Webench is based on equations model to estimate these parameters.

https://www.ti.com/lit/an/slva477b/slva477b.pdf?ts=1649783430083&ref_url=https%253A%252F%252Fwww.google.com%252F

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1083141/faq-how-efficiency-influences-duty-cycle-in-non-isolated-dc-dc-converters?tisearch=e2e-sitesearch&keymatch=duty%252520cycle%252520vs%252520temperature#

Efficiency of buck converter is determined by many factors including the Inductor DCR and FET RDSON that can change as the thermal’s changes with it.

Answer to 3^rd question:

The TPS543C20A has a higher max recommended input voltage of 16V versus the TPS543C20 which has max of 14V. This higher voltage rating comes at a small trade-off in that the TPS543C20A has a slightly higher HS FET Rdson of 3.4mohm compared to the 3mohm HS FET of TPS543C20. For typical low output voltages, this difference in HS FET Rdson on efficiency and thus in Tj to be minimal.

Thanks!

Tahar

0 Ella KIM over 3 years ago in reply to Tahar Allag

TI__Expert 4212 points

Hi Tahar,

Thank you for the information! The materials greatly helps.

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TPS543C20A: How the duty is determined in Webench report