TLF35584 BOOST module loop stability test method

[bennieliu]

Dear Infineon experts:

Currently we have known that we could do TLF35584 boost converter loop stability analysis based on the online simulation tools  from Infineon website.Some customers want to test the loop on the board.So can you advise how to implement the test setup for stability analysis ( for example how to select the injection point?)based on the typical TLF35584 BOOST/buck circuit environment ？

 

 

[AnilKumar]

Hello,

Loop stability Analysis can be performed in Lab using any Bode Analyzer like Bode 100 along with an injection transformer to isolate the output of the Bode Analyzer from the DC operating point of the feedback loop.

Place a low ohmic resistor along the series path from Output to FB pin as shown below.
The disturbance voltage is applied in parallel to the injection resistor using the injection
transformer. The inputs of the Bode Analyzer are connected to either side of the injection transformer. CH1 measures the disturbance signal that is applied to the feedback pin and CH2 measures the signal that appears at the output of the converter. By dividing the voltage at CH2 by the voltage at CH1 we get
the transfer function from the feedback input to the output of the power supply. This transfer function
we call it as loop gain 𝑇(𝑗𝜔).
The measurement of the loop gain is performed in the Gain / Phase mode of the Bode Analyzer Suite.

Thanks

Anil

[bennieliu]

Anil:

Thanks for your feedback ,i've noticed that you delivered a good advice on buck converter !According to our discussion,can you also make some comments on TLF35584 BOOST converter based on typical circuit  ? How to implement the injection point? Thanks a lot again! 

[AnilKumar]

Hello,

For any converter, injection point is always at the Feedback pin as Impedance looking in the direction of the FB pin is much higher than the Impedance looking backward.

See the below diagram on Boost Converter:

Thanks

Anil

[bennieliu]

Anil:

I completely agree with your comment about injection point should be always at the Feedback pin.For this case,it seems that the Feedback pin is inside TLF35584 chip,but we can not  reach  point inside a chip.Am i right?Here is my doubt .Would you help double confirm with this issue?

[AnilKumar · Accepted solution]

Hello,

Sorry, I overlooked the circuit and yes you are right since FB is not exposed outside for Boost, we may not be able to perform Stability Analysis using Bode Analyzer.

But you may check the instability in case in time domain by observing the output voltage under different load steps.

Thanks

Anil