Input capacitors on unused rails

[electricar]

Hello,

is it necessary to connect decoupling capacitors on the inputs of the PMIC if the corresponding outputs are not used?

E.g. if I don't use the SW1A buck converter, do I have to put a decoupling capacitor at SW1AIN?

And if yes, do I have to connect it to a voltage rail or can it let be floating?

The same applies to unused LDOs (VGENs) and VINREFDDR and VHALF. What should I do with the inputs and outputs if they are not used?

Thank you very much in advance.

Kind regards

[diegoadrian]

Hello,

I apologize for the delay.

The only unused inputs that need to be connected to an external voltage are the Vinx inputs.

For that reason, we recommend you to connect those inputs to a voltage from 3.15V/3.3V.

I hope this information can solve your question.

Best Regards,

Diego.

[diegoadrian]

Hi,

Here you have some answers to some of your questions.

2. This is the current consumption of the MMPF0100.

3. We only recommend you to use the capacitors on the pins that we specify in the document.

4. This is defined on the power-up sequence of the MMPF0100.

For your first question, I need to make a deeper research.

Best Regards,

Diego

[electricar]

Hello Diego,

did you find something out about the minimum voltage that has to be applied to the unused inputs?

Thank you in advance.

Kind regards

[diegoadrian · Accepted solution]

Hello,

This is what we recommend to do with the unused pins.

Using this case as an example. Yes, you need to connect this pin to an output of a regulator with voltage less than 3.4V. I recommend you to connect this pin to the SW4, unless the SW4 is also unused, or is greater than 3.4V.

I hope this information can solve your question.

Best Regards,

Diego.

[electricar]

Hello Diego,

what is the minimum voltage that has to be applied to the unused inputs?

How much current is drawn by the unused input voltage rails?

Do I need 100nF caps on the unused voltage inputs?

When do I need to supply the unused voltage inputs? Is there a special timing requirement?

Thank you very much in advance.

Kind regards

[diegoadrian]

Hello,

In this application note of the MPF0100, you can see what you need to do when you are not using a pin.

http://www.nxp.com/assets/documents/data/en/application-notes/AN4717.pdf 

I hope this information can solve your question.

Best Regards,

Diego.

[electricar]

Hello,

thank you for your answer. Just to be sure: does this

mean that you can not connect it to GND if it is unused? It has to be connected to a voltage regulator output which is enabled?

And you don't need any capacitors when it is unused?

Kind regards.