Electronic – the minimum supply voltage for an LM335

analoglm335sensortemperature

The answer to this question is probably staring me in the face, but I just can't see it. I'm attempting to interface with an LM335AZ temperature sensor (datasheet) at 3.3V. The datasheet clearly states that the output voltage is 10mV/K, and that at 25°C and 1mV it should output between 2.92V and 3.04V. What I do not see specified is the minimum voltage it will operate at, and the sensor I have in hand doesn't appear to work correctly at 3.3V.

With a 3.3KΩ resistor the current to the LM335 should be 1mA at 3.3V. If I directly measure the output voltage when supplying 3.3V, I get 2.46V, which correlates to −27°C; if I supply 5V I get 2.93V, or about 20°C. Suffice it to say that I'm not performing these tests outside at the North Pole. 🙂

Does the LM335AZ only work on 5V, or 5V and up?

Best Answer

With 3.3K you are not getting 1mA. You are getting around 100uA.

At 25DegC the LM335 is at 3V. With a Vin of 3.3V you getting 0.3V across the resistor. 0.3V / 3.3K is apx 100uA. If you use a 300Ohm resistor you should be at about 1mA.