LT3092
Production
The LT3092 is a programmable 2-terminal current source. It requires only two resistors to set an output current between 0.5mA and 200mA. A multitude of...
Datasheet
LT3092 on Analog.com
Hello,
I just stumbled upon the LT3092 IC. I want to use it as a constant current source with a DAC generating 40kHz sine wave with an amplitude of about 1V.
I noticed the below schematic in the datasheet. I had a few questions about this schematic. It would be great if someone could help me out with the questions below.
1. The DAC output is wrt a certain ground. Is it fine if I make it common with the 10 ohm resistor ground in the schematic?
2. Do I have to connect an appropriate amplitude voltage source at the "IN" pin and take the current out from that terminal itself? If yes, then is it okay to short the 10 ohm ground and the voltage source ground. If no, then what is the right way of doing it?
Thanks for the post. I attached an LTspice circuit that shows a 1V peak voltage source driving the LT3092 SET pin to make a 40kHz 1mA to 201mA sine wave current through an LED load. The 1V peak voltage source simulates your DAC. The image below shows the circuit and the simulation result. The LT3092 has a minimum load requirement of around 1ma - 0A out is more difficult to achieve. The LT3092 is designed so the OUT and SET voltage are usually about the same, so be careful not to drive SET away from OUT. I used an conceptually simple LED for a load. The voltage source V1 needs to be high enough to ensure there is always around 1.6V or more from IN to OUT of the 3092. Read the LT3092 datasheet for details.
Hi,
I have an update. I recently purchased the LT3092 chip and was trying out the circuit you showed in the LTSpice simulation with the following specifications
1. DC shifted sine wave of peak voltage 3.3V, as in the dynamic range is (0-3.3V) with a frequency of 40kHz.
2. V1 is 5V
3. Instead of D1 I have a resistor of 47 ohm across which I am measuring the output voltage to visualize the current source.
4. R2 in my case is 0 ohm (directly connected the DDS output to the terminal) and R1 is 47 ohm.
This is how the DDS output looks
This is how the voltage measured across the 47 ohm resistor which i put instead of D1 looks.
My questions are
1. Why is the output of the current source looking clipped?
2. Am I doing something wrong by removing R2 and directly connecting the DDS input to the SET terminal?
3. What was the intended function of R2?
Good job getting yourself some hardware to test yourself. You will learn a lot about these clever devices. I think you can answer most of your questions yourself if you read the LT3092 datasheet and understand how the LT3092 works. If you do that you will be able to ask the best questions that will make your circuit as good as possible. Sometimes customers do not notice that the LT3092 has a minimum load requirement - even customers who take a close look at the datasheet - so I am happy to show the excerpt about the LT3092 minimum load requirement from the datasheet Electrical Characteristics Table in the image below:
