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LT3082 Set Pin

speciali7
on Nov 30, 2018

I'd like to use the LT3082 in a DAC controlled mode as shown in the typical applications section of the datasheet, but I'd like to do so without the gain stage shown. This should work as the op amp internal to the LT3082 has very high input impedance, but am I missing some other design consideration?

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    •  Analog Employees 
    on Feb 11, 2020 11:56 PM over 1 year ago

    The gain stage is needed in this circuit because the chosen DAC doesn't have the required voltage range.  If your DAC can reach the highest desired VOUT voltage, you don't need any amplification.

    Another issue I ran into is the LT3082 doesn't tolerate very quickly changing inputs on SET.  You need some slew rate limiting. when you change the voltage.  This is from the datasheet:

    "The second scenario follows improper shutdown techniques in which the SET pin is reset to GND quickly while OUT is held up by a large  output capacitance with light load. The Typical Applications section shows simple, robust techniques for shutting down SET and OUT together."

    I had to add an RC circuit to my application's SET pin to have the regulator shut down correctly.  Here's another note if you really need to have VOUT = 0:

    "Regulation of the output voltage requires a minimum load current of 0.5mA. For a true 0V output operation, return this minimum 0.5mA load current to a negative supply voltage."

    In my case, I was OK with VOUT of .2V, so I used a schottky diode to clamp VOUT.