LM51561H-Q1: The noise difference between with Spectrum spread and without it

Hi Tanaka,

Thanks for using the e2e forum.

I cannot give an absolute value for the noise level reduction of the spread spectrum, as EMI is heavily depending on design, chosen components and layout.

If your design is facing bad EMI performance, I would follow EMI design guides and make optimizations in the frequency ranges where the device fails EMI test.
Please let me know if you have additional questions or need a specific design review.

Best regards,
Niklas

Hello Niklas

I appreciate for your answer.

We are using LM51561HQPWPRQ1.

It is ok not to give me the precise number but still hard to get the valur?

Best regards,

Hi Tanaka,

Yes, there is an application note which compares the EMI performance with and without using spread spectrum with LM5156.
https://www.ti.com/lit/an/snva974a/snva974a.pdf

In figure 3.3., you can see a measurement that shows the spread spectrum reduces noise by approx. 10dB for this application.

Best regards,
Niklas

Hi Tanaka,

I hope the provided apps note was useful.
As there were no further comments, I will close this thread for now.
If you have any additional questions, simply reply below to re-open the thread.

Otherwise, feel free to click on the resolved button.

Thank you and best regards,
Niklas

Hi Niklas

it was confirmed that the pulse skip operation was actually performed by the measurement.
In the simulation under the same conditions, there is no appearance of pulse-skipping operation.
Is it a problem of conditions that is not reproduced in the simulation, or does the SPICE model not have that function in the first place?

I am using Ansys simulator.

Best regards,

Hi Tanaka,

The PSpice for TI model of LM5156 does not simulate all features of the physical device.
You can see in the notes inside the model which features can be simulated:

Frequency dithering and thermal behavior are NOT simulated by the PSpice model.

Best regards,
Niklas

Hello Niklas

Thank you for telling me.

So you mean that TI does not have simulation model function for this device?

best regards,

additional question.

Could you send me the LINK of application note?

best regards,

Hello Niklas

Thank you for your support.

Could you send me the original file of below pics?

Best regards,

Hello, 

As Niklas mentioned, all the TI PSPICE files can be downloaded from the following link: https://www.ti.com/product/LM5156#design-tools-simulation

Kind regards,
EM

Hi Tanaka,

As there were no further comments, I will close this thread for now.
If you have additional questions, please reply below to re-open the thread.

Otherwise, feel free to click on the resolved button.

Thank you and best regards,
Niklas