# Digital Pot Help for a Noob

Joined Feb 15, 2012
17
Hello Everyone.

I'd like to start by saying that my electronics knowledge is very very limited... But i'm very quick to understand concepts and theories.

Im currently building a circuit using a Murata okr-t6-w12 - Data sheet is on-line if you search for it. (not sure if noobs can post links)

Its a DC-DC Voltage Converter and on the datasheet is states the following resistances needed to obtain the output voltages.

The range i am interested in (with its related resistance levels) Is Highlighted in BOLD Below:

6 V. - 218.5 Ohms
5 V. - 268 Ohms
3.3 V. - 436 Ohms
2.5 V. - 619 Ohms
1.8 V. - 978 Ohms
1.5 V. - 1300 Ohms

I need a digital pot that can help me achive these figures without going too far either side of them.
Also ideally i would like it to have as many steps as needed in order to adjust the voltages by 0.1v with each click. Otherwise it can be 0.05v per click.

Can anyone please assist me in working out what exactly i should be looking for?
Many thanks

#### praondevou

Joined Jul 9, 2011
2,942
6 V. - 218.5 Ohms
5 V. - 268 Ohms
3.3 V. - 436 Ohms
It could be a 1k E-pot in series with a 218Ω resistor (that's actually from the E192 series, but you could combine resistors to obtain the value or just take the next easily available value).

The 1k E-Pot has to be in parallel with 279Ω which is also to be obtained by combining resistors.

Example for a 1k E-pot: http://search.digikey.com/us/en/products/X9313ZSZT1/X9313ZSZT1CT-ND/1034225

This one has 32 steps so it will be 84mV per step.

The total resistance can then be changed from 218R to 436R.

Have a look here for resistor values: http://www.pc-control.co.uk/resistor-eia.htm

#### Ron H

Joined Apr 14, 2005
7,014
You might be able to use a digital pot as a rheostat if you can live with the resolution limits, the contact resistance, and the resistance tolerance. You can overcome the last two by putting the supply in a feedback loop, digitizing the output voltage and tuning the rheostat for the desired voltage. Resolution limits might be your downfall.

#### crutschow

Joined Mar 14, 2008
24,750
One large limitation on a digital pot is that the resistive element voltages must normally stay within the supply rails and common of the chip. Thus your control circuit would have to have a common ground with the power supply (or control terminal) and the terminals you are controlling would need to stay within those voltage limits.