Question about LT3081

[TiTanerCZE]

Hi, I have a question about LT3081. Set pin is connected to internat opamp. Set current is on this pin, fixed current is 50uA, but i dont want to control this circuit using resistor, or digital one. I want to control this IC using DAC, or using uC.
I cant find any simple project done using this LT3081.

Is it possible?

This is what i came whit:

[TiTanerCZE]

OPAMP is random...

[BU508A]

Have you seen this?

http://www.linear.com/solutions/1256



Maybe you'll find something in the related documents on the LT website.

[newbrain]

Page 18 of the datasheet:

The LT3081 uses a unity-gain follower from the SET pin
to  the  OUT  pin.  Therefore,  multiple  possibilities  exist
(besides  a  SET  pin  resistor)  to  set  output  voltage.  For
example,  using  a  high  accuracy  voltage  reference  from
SET to GND removes the errors in output voltage due to
reference current tolerance and resistor tolerance. Active
driving of the SET pin is acceptable.

It's possible, and works as expected: Dave's µSupply does just that (with a 3080) and my home built PSU also (with a 3083).

You will need to provide some gain (using the op-amp) to scale the DAC output (usually 3.3 or 5V) to the desired range.

[RustyShackleford]

Page 18 of the datasheet:
For example,  using  a  high  accuracy  voltage  reference  from
SET to GND removes the errors in output voltage due to
reference current tolerance and resistor tolerance. Active
driving of the SET pin is acceptable.

I've done it this way, and it works fine.   It also sidesteps the issue of leakage around the SET pin (discussed on p.12 of LT3081 datasheet).   

I'm curious why you don't want to use a digital resistor though (though I guess the quote explains on likely reason :-) ).   I am building a multi-channel digitally-adjustable current source around an LT3081, and am torn between using a digital pot or a DAC (on the SET pin).   The DAC has the aforementioned advantages, but in addition to needing to scale the voltage, you probably will also need to buffer it (to sink the 50ua from the SET pin); of course a single opamp can do both.   A digital pot (e.g. http://www.mouser.com/ds/2/268/22059a-51937.pdf) sidesteps this, and all you need to drive is an SPI interface.