I'm not sure what happened, maybe I was tired and did a short, no idea.
But with a 10k resistor (instead of the original 220) between the Vdd and +5V, and with a 1uF capacitor between Vout and GND, I'm getting accurate readings on the MCP9700.
For further reference, is it possible to damage a capacitor in any way? Maybe that's what happened? I couldn't find it anymore today so I took a fresh one and it's fine.
Also, if I put a 220 ohms resistor as suggested in the datasheet instead of a 10k along with the 1uF capacitor, I'm getting wrong readings (ie too much voltage coming out on the analog of the MPC9700). Same if I only put a 1uF capacitor without any resistor. Is there a way to calculate what's the best resistor value to go with a capacitor in that specific case?
The datasheet has this to say, am I misreading or missing something?
4.3 Layout Considerations
The MCP9700/9700A and MCP9701/9701A family does not require any additional components to operate. However, it is recommended that a decoupling capacitor of 0.1 ?F to 1 ?F be used between the VDD and GND pins. In high-noise applications, connect the power supply voltage to the VDD pin using a 200? resistor with a 1?F decoupling capacitor. A high frequency ceramic capacitor is recommended. It is necessary for the capacitor to be located as close as possible to the VDD and GND pins in order to provide effective noise protection. In addition, avoid tracing digital lines in close proximity to the sensor.