I would like to use STuW81300 on my device but I don't ensure how to design Internal LDO output. I need to help.

Yigit Yalcinkaya · ‎2022-03-23

When I read the STuW81300 datasheet, I learned to need to use 10uF and small resistance at the output of LDO. I will share the Application Diagram below this.

But when I read the UM2218 User manual, I saw the bellow figure.

I don't know if I need that many links.I am waiting for your comments and help.

Peter BENSCH · ‎2022-03-23

I had already pointed you to section 7.13 of the data sheet, but your design is missing the series resistors:

Proper stability and frequency response are achieved by connecting 10 μF load capacitors at the regulated output pins. The optimal configuration is achieved by connecting a small resistor in series with the capacitor in order to guarantee the controlled ESR required to ensure the proper phase margin, together with the best performance in terms of noise and PSRR.

Like most LDOs, the load capacitors in this device require a certain minimum ESR value. Ceramic capacitors (MLCC) usually do not have this, so you have to insert the series resistors seen in the EVB.

In the circuit of the EVB, however, you can also see some 0-ohm resistors, which of course you don't necessarily have to insert, they rather serve the purpose of being able to easily insert them into the EVB later on, if necessary.

In conclusion, no one can say that the STuW81300 will work correctly if these instructions are followed. There are many more important things to consider: RF design and layout, board material if necessary, crystal parameters, type of passive devices etc etc. For this reason, an STuW81300-EVB is provided with which to make initial investigations and comparisons.

But at least you would have laid the foundation for hopefully low-noise and stable LDOs.

Good luck!

If the problem is resolved, please mark this topic as answered by selecting Select as best. This will help other users find that answer faster.

/Peter

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Peter BENSCH · ‎2022-03-23

Welcome, @Yigit Yalcinkaya, to the community!

what do you mean with "many links"?

The first picture (figure 26 from the data sheet) shows only a simplified block diagram to avoid irritation due to the external components required.

In section 7.13 of this data sheet you will find more information about the LDOs included and why series resistors are necessary in addition to the filter capacitors.

Does it answer your question?

Regards

/Peter

In order to give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.

Yigit Yalcinkaya · ‎2022-03-23

Thank you for your kind and quick response!

I wanted to say many connections. Sorry I used the wrong word.

If I will make like a figure 16, do I make this true?

For instance, I made the below schematic.

If I add a series resistor to this diagram as in figure 16, will it be correct?

If I do design as in figure 16, will the STuW81300 work correctly?

Peter BENSCH · ‎2022-03-23

I had already pointed you to section 7.13 of the data sheet, but your design is missing the series resistors:

Proper stability and frequency response are achieved by connecting 10 μF load capacitors at the regulated output pins. The optimal configuration is achieved by connecting a small resistor in series with the capacitor in order to guarantee the controlled ESR required to ensure the proper phase margin, together with the best performance in terms of noise and PSRR.

Like most LDOs, the load capacitors in this device require a certain minimum ESR value. Ceramic capacitors (MLCC) usually do not have this, so you have to insert the series resistors seen in the EVB.

In the circuit of the EVB, however, you can also see some 0-ohm resistors, which of course you don't necessarily have to insert, they rather serve the purpose of being able to easily insert them into the EVB later on, if necessary.

In conclusion, no one can say that the STuW81300 will work correctly if these instructions are followed. There are many more important things to consider: RF design and layout, board material if necessary, crystal parameters, type of passive devices etc etc. For this reason, an STuW81300-EVB is provided with which to make initial investigations and comparisons.

But at least you would have laid the foundation for hopefully low-noise and stable LDOs.

Good luck!

If the problem is resolved, please mark this topic as answered by selecting Select as best. This will help other users find that answer faster.

/Peter

In order to give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.