Electronic – LT3080 Set pin voltage

linear-regulatorpower supply

LT3080 documentation states under absolute maximum ratings:

SET Pin Voltage (Relative to OUT) ±0.3V

(http://cds.linear.com/docs/en/datasheet/3080fc.pdf page 2)

In the documentation there's also figure named "Lab supply" (bottom of page 18) with 2 LT3080s. I simulated this circuit in LTspice and it seems that in constant voltage mode the current limiting LT has SET about 1V higher then OUT. Similar thing happens with voltage setting LT in constant current mode.


green trace is OUT, blue is SET (both on U1), circuit set to 10V 1A, load draws 10mA

Is this how this should work?

Note 7 about SET pin current states:

SET pin is clamped to the output with diodes. These diodes only
carry current under transient overloads

How is this situation supposed not to damage these diodes (in steady state)?

Best Answer

I asked LT and they answered me (surprisingly fast) this:

Your point is valid in that the nature of the Lab Supply application circuit violates the SET-OUT abs. max. However, this is the way the circuit is supposed to work. Your simulation results that also sound correct.

In the case of the Lab Supply application circuit, you can ignore the SET-OUT abs. max. This is because SET is not being driven externally to 1V away from OUT. Instead, SET is driven internally by a relatively week 10uA current source which can’t drive enough current through the parasitic OUT-SET diodes to cause the LT3080 to misbehave or damage itself.

So I guess that 0,3V absolute maximum means that I can't use external voltage 0,3V higher or lower then OUT.

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