# DC/DC Converter Trim function

I found a DC/DC Converter to convert a voltage of 15 to 24V to 5V P783F-S. The P783F-Q24-S5-S (page1) accepts an input voltage of 8 to 36V and converts it down to 5V.

On page 6 there is a trim table, I don't really understand it. There is Vout nom. and Vout adj., if I want an output voltage of 5Vdc do I need a trim resistor? Also will the DC/DC Converter automaticaly step down any voltage between 8 and 36V to 5V?

Also on page 1 there is an output current of max. 3A stated. If the input voltage is 8V or 36V will this affect the output current?

The trim function is only for output voltage adjustment, if so desired. Without trim (neither R1 nor R2 placed), a P783F-Q24-S5-S outputs 5 V (its nominal voltage).

The table suggests that you can decrease the output voltage by populating R1 - e.g., if you make it 195k, you'll get 4 V on the output. You can also increase the output voltageto 5.5 V or 6 V by populating R2 according to the table.

Also will the DC/DC Converter automaticaly step down any voltage between 8 and 36V to 5V?

Yes, that's what the relevant row of the "INPUT" table on page 2 says.

Also on page 1 there is an output current of max. 3A stated. If the input voltage is 8V or 36V will this affect the output current?

The derating curves show that at high temperatures above 75 degrees Celsius, the power must be derated for high input voltages. Below that temperature, the safe operating area is governed solely by output power (i.e. output current * 5 V) as long as the input remains between 8 and 36 V.

Note that for 9 V and higher output voltage models, the derating curve is a bit different; regardless below 60 degrees you are still limited solely by output power.

• @nanofard but there is only R1 or R2 stated. I only need one of those resistors to increase/decrease the voltage? So the output power stays the same below 70°C and the output current therefore should remain at 3A, when the output is 5V Commented Feb 1, 2022 at 18:20
• @electrococuk The datasheet is somewhat sparse, but based on how I expect them to implement feedback, yes, just that one resistor. The output current can remain up to 3 A as long as you haven't trimmed it away from 5 V, but of course the current is lower if the load draws less. Commented Feb 1, 2022 at 18:23
• @nanofard thank you. Also on page5 there is a small circuit with a inductance called LDM. What does LDM mean? Is this a inductor with an iron core? Commented Feb 1, 2022 at 18:24
• also on page5 there are 2 values for C4 given. Which one should I choose? Commented Feb 1, 2022 at 18:27
• @electrococuk The inductor core isn't specified but it's likely an inductor with a low-loss core (whatever you can get that meets your size and cost needs while achieving 22 uH of inductance). As for the two capacitors, read the first column of the table. Do you care about reducing EMC emissions or increasing EMC immunity? Commented Feb 1, 2022 at 18:28