# LT3081 Precision Current Limit Programming

I am trying to precisely control current limit of the LT3081 IC following this paper, page 12, schematic on page 14, but by using a microcontroller.

I'm controlling the output voltage with a 10kOhm, 8 bit, digital potentiometer, which I feed with 1.2mA constant current to make it regulate the output voltage between 0 and 12 V.

I'm trying to limit the output current from 1 mA to 1A, idealy with 1 mA step, without using more expensive 10 bit digital pots. By using a similar configuration as shown in the schematic for higher accuracy (pot + paralel res + series res), using one 10k, 8 bit, digital pot and considering the wiper resistance, I got to a point where I can control the current limit with a 7 mA step at lower values, and 2 mA steps as I get closer to 1 A limit.

Equation for current limit(from datasheet): RILIM = ILIMIT/360mA/kΩ + 450Ω

Simplified equation: RILIM = ((ILIM*1000)/0.36) + 450

Simplified schematic:

simulate this circuit – Schematic created using CircuitLab

My question is: Is there any other way for a more precise current limit control without using a higher step count (bit) digital pot?

• How do you expect to get 1000 steps in the output of a device with only 256 different settings? May 9, 2018 at 16:25
• Maybe you could get the two additional bits by switching in series resistors using MOSFETs? Just getting a 10b digital pot would be the best option, though. May 9, 2018 at 16:35
• Yes, I agree that 10b would be the best option. I need 1mA step upto 100mA, after that 10mA step is ok. Im currently testing 1k 8b + 10k 8b in series, but i think i will just go with 10 bit 10k and close this question. May 9, 2018 at 16:38
• The Imon pin is a current you have to sink, and you don't need to sink it into the output. Look at a the datasheet examples on current sharing on page 22. You could provide you own current measurement and either sink a current from Imon or sink a current from Set and perform foldback that way. May 9, 2018 at 19:13