WEBENCH® Tools/TPS57114-Q1: Result of Start up simulation

K.Hamamoto

Guru 12155 points

Part Number: TPS57114-Q1

Tool/software: WEBENCH® Design Tools

I have a question about WEBENCH result. (Please see the below.)

https://webench.ti.com/appinfo/webench/scripts/SD2.cgi?ID=194534::power::hamamoto-k@clv.macnica.co.jp

The result of simulation was unknown behavior such as oscillation on Vout and Inductor current.

What is the oscillation during startup? And why is the behavior happen?

Regards,

Koji Hamamoto

over 8 years ago

0 Nikhil Gupta (Product Folder Models) over 8 years ago

TI__Mastermind 39210 points

Hamamoto-san,

I am unable to open your design link since that is only shared with that email ID in the link. Can you do a public share instead?
Otherwise, can you try reducing the switching frequency by changing the RT resistor manually. The device may be going through Min On Time regime during Startup but can not say for sure without looking at the actual design.

0 K.Hamamoto over 8 years ago in reply to Nikhil Gupta (Product Folder Models)

Guru 12155 points

Hi Nikhil-san,

I am sorry for the design link.

I pasted the new link. Please see the below.

webench.ti.com/.../SDP.cgi

regards,
Koji Hamamoto

0 Nikhil Gupta (Product Folder Models) over 8 years ago in reply to K.Hamamoto

TI__Mastermind 39210 points

Hamamoto-san,

It looks like you have manually modified the Fsw of this circuit to 2MHz. If I create your design from WEBENCH, the default frequency comes out to be ~ 1.1MHz (see startup sim 2 below). This gives monotonic startup.

webench.ti.com/.../SDP.cgi

When you increase the frequency to 2MHz (sim 3), the switching period reduces that seems to have an impact during startup. This is especially evident around the point where the frequency foldback comes into picture (transitioning from 50% freq to 100% frequency - Figure 6 in www.ti.com/.../specifications and also due to the interaction with the Min ON time pulses during Startup. If you are looking for maximum frequency of operation, you may want to reduce the FSW from 2MHz down to see where you start getting more monotonic startup.

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WEBENCH® Tools/TPS57114-Q1: Result of Start up simulation