i.mx6sl, MMPF0200 PMIC question

[kentmeyer]

We are planning to use the MMPF0200 with a 3.3V input voltage and suspect

that there will be problems with the SW2 output.

Can SW2 operate with 100% duty, i.e. can the SW2 PMOS be persistently

on if/when SW2 is on?

Can SW2 correctly operate if its output voltage is set equal to its input voltage

(Vsw2=Vsw2in) and Lsw2=0 (a wire in place of the inductor)?

-- Kent

[reyes]

Hi Kent Meyer,

All the regulators except SWBST are step-down which meaning the input has to be higher than the output. Our recommendation is 250mV headroom for the regulators. So if they need a 3.3V output, the input has to be at least 3.55V for the LDOs and the bucks.

And about your suggestion about to use a wire instead an inductor, SW2 is a Buck Regulator, so the inductor is needed for the LC circuit to filter the pulses to create a smooth DC voltage.

Have a great day,
Jose Reyes

-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

[vadimaleynikov]

Hi Jose Reyes,

I work with Kent Meyer and have some follow-up questions.

You explained the regular DCDC operation. But we will have to use it in an unusual way and would like to know will it be correct. Specifically, we would like to know:

1. How will SW2 operate when its output voltage is set equal to its input voltage (Vsw2=Vsw2in)?

2. Can SW2 operate with 100% duty, i.e. can the SW2 PMOS be persistently on if/when SW2 is on?

Best regards,

Vadim Aleynikov

[reyes]

Hi,

[A1] As mentioned, SWx buck regulators are step-down which meaning the input has to be higher than the output.

I just tested it using the MMPF0200 Evaluation board and I can confirm that there is a drop on the SW2 output voltage, when VSW2IN = 3.3V and SW2 output voltage is set to 3.3V, the actual output voltage drops to 3.28V.

[A2] No, SWx buck regulators (switching regulators) operate with a max duty of about 90%, and unfortunately on the MMPF0200 it is not possible to make them work as an LDO (100% duty regulator).

Have a great day,
Jose Reyes

-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

[vadimaleynikov · Accepted solution]

Hi,

I understand, thank you.

Unfortunately I could not find the Correct Answer button.

Best regards,

Vadim