Adjustable Step Down Module - Swap Potentiometer with Resistors?

Thread Starter

haukeg

Joined Dec 9, 2018
66
Hi, I am using a DC-DC Buck Converter that has a MP1584EN Regulator (Amazon Link) and am taking 12v to 5v for Vin on a micro controller.

This module is pretty tiny, and the Pot for adjusting is also super fragile and sensitive. I'd like to pull it and replace with resistors to lock in my 5v out so it doesn't get adjusted inadvertently.

I could use some help on determining how to swap in the resistors, I've traced the 3 posts on the Pot to the Regulator and found one goes to the Feedback Pin 4 on the MP1584EN (#3 on photo) and the other two are connected to Vout+ and the Switch Node Pin 1 on the MP1584EN (#1 & 2 on photo).

Looking for instructions on replacing the Pot with fixed resistors somehow. Thank you!

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KeithWalker

Joined Jul 10, 2017
1,216
To find what value you need, first set the potentiometer to give the required output voltage. Disconnect all power and remove the pot from the circuit board being careful to not move the wiper on it. When it is out of the circuit, measure the resistance between terminals 1 and 3. Connect a fixed resistor with that value to the circuit board to replace that section of the potentiometer (between 1 and 3). If you don't have a resistor close to the value you need, you can make it by using series and parallel resistors.
Regards,
Keith
 
Last edited:

Thread Starter

haukeg

Joined Dec 9, 2018
66
Thank you @KeithWalker and @crutschow for the replies. A glob of glue isn't a bad idea actually! However I pulled the Pot off already.

KeithWalker - I have that value so I am good, will place the resistor I need between 1 & 3. I can just leave 2 open (disconnected) then?
 

Thread Starter

haukeg

Joined Dec 9, 2018
66
Solved. I got a good pointer on another forum for the proper resistance calc's if ever needed for other voltages with this regulator, sharing in the case anyone finds their way here for similar needs:

Remove the pot and solder a 43K 0805 smd resistor between terminals 2 and 3. That should provide 5V as R2 in most of these modules is 8K2. With R1 at 43K and R2 at 8K2, vOut is 0.8 * (43+8.2) /8.2 where 0.8 is the Vref of the MP1584.
https://www.monolithicpower.com/en/documentview/productdocument/index/version/2/document_type/Datasheet/lang/en/sku/MP1584/document_id/204
 
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