I bought three MCP9701 temperature sensors in SOT23-3 package made by microchip to use for doing some PWM controlled fan speed.
The analog output of the temp sensor is the following equation:
Vout = Tc x Ta + V0
Tc = Temp Coeff = 19.5mV/°C
Ta = Ambient temp
V0 = Vout at 0°C = 400mV
So for an ambient temperature of around 25°C I should get a Vout of around 800mV.
The first one I tried gave an output of around 2.3V when powered at5V.
The 2nd one has an output of 2.9V, also powered from 5V.
I'm not sure what's going...
I've soldered these onto adapter boards so that I can put them on a breadboard for testing.
I did not put my soldering iron on the pins longer than I usually do, which isn't long, so I didn't fry them. Soldering these went without issues.
I've tried adding a pull-down but that didn't change much to the output.
It's a 3 pin chip, I checked and rechecked the connections.
There is no circuit, I just connected GND and Vdd and measured the output with a multimeter and scope.
I cannot believe Murphy got me twice in a row with 2 dead temperature sensors out of the tape.
I haven't tried the last one yet.
Hoping someone can help.
Wish I had some magic bullet for ya, but I don't. I looked through the datasheet and there is no reasonable explanation for your results that I can see...other than:
1. The chips are bad or not what you think they are. Were they purchased from a reputable source? Do they have markings consistent with Microchip's markings as per the data sheet?
2. There [is] a connection problem. You checked, I know. Maybe check while assuming nothing at all. Including whether the carrier board is wired as you thing, your breadboard is not messed up, your supply really is 5V - all that stuff.
There is no way that I can see for a Vo of 2.3V unless your temp is ~97 C [(2300-400) / 19.5]. No amount of error or need for calibration or self-heating could give you that in my view.
I'm curious how this works out so please let us know.
edit: does Vo change at all if you hit it with a hair dryer or heat gun or otherwise raise the temperature?