Tool/software:
Hello TI E2E Team,
I am working on a design with the TPS54260DGQR in WEBENCH Power Designer and have encountered an inconsistency in the simulation results that I would like to understand.
Design Parameters:
- Vin: 8.53V - 9.0V
- Vout: 7.8V
- Iout: 1.3A
I have two WEBENCH reports for what should be the same design. For clarity in our discussion, I have named the generated PDFs as follows:
- Report A:
TPS54260DGQR 9V to 7V8 1.3A_Wrong_Transition.pdf - Report B:
TPS54260DGQR 9V to 7V8 1.3A.pdf
Both reports show nearly identical component selections (BOMs) and identical calculated "Operating Values" in their tables, including a switching frequency of ~282.4 kHz (set by Rt = 442 kΩ).
However, the simulation graphs for Load Transient and Input Transient are vastly different:
-
In Report A ("Wrong_Transition"):
- For the Load Transient, the simulation parameters clearly define a current pulse from 1.3A to 0.13A. However, the
IOutplot shows a constant current of 1.3A throughout the simulation; the pulse is never executed. Consequently, theVOutplot only shows steady-state ripple with no transient behavior. - For the Input Transient, the simulation does not apply any change to Vin, showing a steady-state plot instead.
- For the Load Transient, the simulation parameters clearly define a current pulse from 1.3A to 0.13A. However, the
-
In Report B (the correct one):
- Both the Load Transient and Input Transient simulations execute correctly, applying the specified stimulus and showing the expected VOut response...
Upon investigation, I discovered that the key difference in generating the reports was that for Report B, I had explicitly enabled the "User Preferred Frequency" option and set it to 282 kHz. For Report A, this option was not set.
My question is:
Why does the simulation engine appear to fail to correctly execute or represent the dynamic simulations (Load/Input Transient) when the frequency is only set implicitly by the resistor Rt, even though the final report correctly calculates and displays this frequency in the operating values table? Is this an expected behavior, or could it point to a potential bug in the simulation setup process?
I have attached both PDF reports for your reference. A public shareable link to the WEBENCH design is also provided below.
TPS54260DGQR 9V to 7V8 1.3A_Wrong_Transition.pdf
TPS54260DGQR 9V to 7V8 1.3A.pdf
webench.ti.com/.../SDP.cgi
Thank you in advance.
