MP9488 design questions

DC-DC Power Converters
#1

Hello,
I’m tryin to design a buck DC/DC converter using the MP9488 IC.
These are the main parameters:

Vin: 325 Vdc max
Vout: 24 or 48 Vdc
Iout: the maximum possible (300 mA?)

I’m in trouble with the measure units to be used for the calculations (the various equations on the data-sheet), more specifically:

  1. I guess that everywere the current values are in mA, is it right?
  2. What is the unit for L (inductor)? H, mH, µH?
  3. The same for Fsw: Hz, kHz?
  4. The same for Cin and Cout: F, µF, nF?
  5. The same for Tminoff: s, ms, µs? (I guess µs, but please confirm)

Last question: is it possible to parallel two or more devices? If yes, what are the main precautions to be taken?

Thank you in advance for a prompt reply.

#2

Hi yoba.basile,

Thanks for your question.
Yes, if the current value ends in mA, then the unit is in mA. The datasheet might also refer to uA or A.
Please elaborate on what inductor, capacitor, frequency you’re referring to. It should have a specified unit. If you’re trying to decide on a value to use in the equations, you determine the value you want to get the desired output.
Tminoff is in us, the unit is specified in the very right most column on page 4 of the datasheet.

Thanks,
Cindy

#3

Dear Cindy,
thank you very much for your reply.
Probably My questions where non so clear, I would need to know what kind of unit I have to use in the following equations (refer to data-sheet):

Equations No. 3 page 12 and No. 8 page 15:
L is in Henry? Milli Henry?
(if, for example, I chose a 1.2mH inductor, what is the right number to be inserted in the equation? 0.0012 or 1.2?)

Equation No. 7 page 15:
Fsw is in Hz? kHz?
Cin is in Farad? Micro Farad?

Equations No. 9 page 15:
fs is in Hz? kHz?
Co is in Farad? Micro Farad?

Please be also so kind to answer to the last question of My previous message:

  • is it possible to parallel two or more devices? If yes, what are the main precautions to be taken?

Thank you again.

#4

Hi,

The inductance value you input will be in Henry. So, if you choose a 1.2mH inductor, you need to use 0.0012H in the equation. This is the same for frequency (use Hz), as well as capacitance (use F).
I’m double checking on the paralleling precautions. Will update once I hear back.

Cindy

#5

Dear Cindy,
thank you for the answers.
Sorry but, on My previous message, I missed to ask you some clarification also for the equation No. 8 at page 15:

Tminoff: µs or s?
Ipeak: mA or A?

I guess s and A, but please confirm.

Forgive me, but the results I get using µs and mA would seems wrong.

Thank you again.

#6

Hi,

Yes, it will be in seconds and Amperes. It should never require you to substitute in a submultiple of its actual unit, unless stated.

Thanks,
Cindy