Setup: an external MCU is connected via a DIN Connector (// par lines) to the NTC temp sensor. It applies a voltage of 3.2V over a 2.2K resistor.
the internal MCU is reading the same value of that voltage over the NTC.
- When the external MCU is not connected, the internal MCU needs and internal VCC to be applied ( symbol SWITCH)
- The voltage of the internal VCC is not the same as the external.
- How can i prevent that the ext MCU get's damaged, or get's false readings.
- the external MCU can be plugged in or disappear at any time;
I taught to put a diode in between A and B, but then there is the Forward Voltage drop that will influence the readings.

Thanks in advance for your attention

 

Use schottky diode to get low Vf.

Or http://www.analog.com/en/search.html?q=low diode 15 mV Vf.....

Regards, Dana.