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I bought an LM2596 board from amazon, and I want to control it's output voltage from an arduino. My plan so far is to replace the trimpot with a network of 2 resistors and a AD5206. One resistor will be in parallel and one in series with the AD5206 to clamp the output voltage between 3V and 11.4V:

schematic

simulate this circuit – Schematic created using CircuitLab

The only problem is, from the data sheet for the LM2596:

When using the adjustable version, special care must be taken as to the location of the feedback resistors and the associated wiring. Physically locate both resistors near the IC, and route the wiring away from the inductor, especially an open core type of inductor.

If I build this circuit on a breadboard PCB (with solder) and then wire it to the trimpot terminals on the board, will it be too noisy? The switching frequency is 150kHz.

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The main problem you will have is the voltage that the AD5206 will see. It is only rated for voltages on any of the pot connections that are equal to (max) or within the range Vdd to GND. I suspect that the circuit diagram for the LM2596 module will be something like this: -

enter image description here

Note the position of the 10k POT in the circuit. Basically it's connected to the output terminal and although you indicate 680R in series with it, if you "dial-up" an output voltage that is too high the pot terminals may go beyond the absolute maximum ratings specified in the data sheet.

If you can guarantee that the POT won't go beyond Vdd to ground you then have the problem of the POT's capacitance to ground. If you read the data sheet there is typically 60pF from each wiper to ground (internal) and this could cause all sorts of problems with stability on the regulator (and noise of course).

What I would recommend is that you try the circuit with an external regular pot and add the parasitic components specified in the POT's data sheet and see if the circuit goes unstable.

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  • \$\begingroup\$ I wasn't aware of the voltage limit on the AD5206, that is a deal breaker. With this configuration the voltage drop could be as high as 9.5V. Can you think of another way I could control the board from an arduino? \$\endgroup\$ Sep 12 '15 at 14:56
  • \$\begingroup\$ The normal voltage seen at the FB input is in the realm of 1.23V. On that basis, if your logic supply is no-less than that feedback voltage you could replace R1 with the digipot in the diagram above but, I'd be tempted to put a zener diode across FB to ground in case things went wrong as they do when prototyping something. \$\endgroup\$
    – Andy aka
    Sep 12 '15 at 16:00

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