PMP4844: Capacitor inductor calculation

Sarumathi R

Intellectual 480 points

Part Number: PMP4844

Please provide the below details,

1.RIN1 to RIN4 resistor calculation details.

2.Output inductor and output capacitor calculation

over 4 years ago

0 Robert Taylor1 over 4 years ago

TI__Expert 5425 points

Hi Sarumathi,

I am not sure what resistors you are referring to, RIN1 - RIN4, are these from the PMP4844 schematic?

For the output inductor and output capacitor you can calculate the values the same way you would for a buck converter.

Thanks,

Robert

0 Sarumathi R over 4 years ago in reply to Robert Taylor1

Intellectual 480 points

Hi Robert,

In PMP4844 schematics, I need resistor calculation for R9,R13 and R11,R10

0 Brian King over 4 years ago in reply to Sarumathi R

TI__Intellectual 2745 points

Hi Sarumathi,

These resistors form dividers to internal comparators for input under voltage and input over voltage. The thresholds of the comparators are listed in the UCC2897A datasheet, and described by equations 21 and 22 of the datasheet (on page 31.)

thanks,

Brian

0 Sarumathi R over 4 years ago in reply to Robert Taylor1

Intellectual 480 points

In PMP4844, the input voltage range is 18-54,so the nominal voltage may be 48V,

But in our power requirement, the input range is 20v-32v, so our nominal input voltage is 24v, and output voltage is also 24 v.

I got one equation from http://www.ti.com/lit/an/slva477b/slva477b.pdf for inductor and capacitor calculation

If I calculate the Inductor value as in the above link I am not able to get the right value.

Please suggest any solution for that?

or shall i use the same inductor/capacitor value which is in the PMP4844

0 Brian King over 4 years ago in reply to Sarumathi R

TI__Intellectual 2745 points

Hi Sarumathi,

You can safely use the same output inductor and capacitor as used in the reference design, since your input range falls within the input range of the reference design.

If you want to use the buck equations for selecting the output inductor, you will need to multiply your input voltage times the turns ratio of the transformer (multiply your input by a factor of 2).

thanks,

Brian

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PMP4844: Capacitor inductor calculation