Temperature Step in a .TRAN Simulation?

LTSpice or regular?

I'm pretty sure you can do it with a .STEP or a .TEMP command in LTSpice.

.STEP isn't the same as a step in temperature _during_ the simulation run.

.STEP simply applies a data change at the _beginning_ of a run.

I want, during a transient solution, to have a temperature change to test a temperature-related shutdown mechanism.

I suspect I will have to do a replacement in subcircuits...

TEMP => V(MyTemp)

and fudge it with a voltage step :-] ...Jim Thompson

Easy in LTspice.

.step temp -55 125 10

Cheers

Phil Hobbs

Ooh ouch. So ideally you'd like to make sure that your temperature detection/shut down works correctly as temperature is changing dynamically?

I think I'd separate the circuit into part A and part B, where part A is the temperature sensor and part B is the rest. Characterize part A over temperature, fake its behavior in a subcircuit, then make sure that part B responds correctly to the changes in part A at a variety of different temperatures.

It'll probably be valid, unless the temperature shows strong gradients across the chip or changes as rapidly enough to be close to the time constants of any RC pairs.

Yes. How I ended up fudging is sort of round-about, but it works...

In the actual circuit there is the equivalent of an LM94022 temperature sensor with GS0 and GS1 both set to 1's.

Internally to the overall circuit the output voltage of the LM94022 drives a comparator (with hysteresis) to effect the thermal shutdown.

Fortunately this voltage also comes out on a pin, so that the user can monitor temperature, if he wants (to me, not very useful :-)

Since I modeled the LM94022 for this application in the first place, I realized that the LM94022 has a weenie output, limited to +/-150uA.

So I made a test tool, an equivalent to an LM94022, but with a voltage source output, replaced every instance of "TEMP" in the equations with "V(MyTemp)", where "MyTemp" is an input pin.

The output of this test tool overdrives the internal LM94022 output, if I apply a voltage to pin "MyTemp" equal to the desired temperature.

So I can apply a ramp to "MyTemp" and watch the thermal shutdown function under transient conditions.

Works great!

...Jim Thompson