Hello. I want to protect nRF51822 ADC input from emergency case of overvoltage (up to 24V). I don't want to use external diodes as any GPIO pin already has internal clamping diodes. I need to know maximum current or maximum power dissipation that can withstand internal clamping diodes to calculate necessary resistance for external current limining resistor. So is there any information on this parameter?
On second thought the forward voltage drop across the diode will considerably vary depending on the ambient temperature and current. So I still need to use circuit as in the attached image and and in order to avoid 3.3V supply voltage rise I need to calculate so that the average current drawn from the 3.3V power source in normal mode was much greater than the current that will go through the resistors R1 and R2 in emergency case of appearing 24V at Point_1. I think I'll just limit current through clamping diode to 250uA as most uC's have a maximum current through clamping diodes somewhere about 1-2mA.
On second thought the forward voltage drop across the diode will considerably vary depending on the ambient temperature and current. So I still need to use circuit as in the attached image and and in order to avoid 3.3V supply voltage rise I need to calculate so that the average current drawn from the 3.3V power source in normal mode was much greater than the current that will go through the resistors R1 and R2 in emergency case of appearing 24V at Point_1. I think I'll just limit current through clamping diode to 250uA as most uC's have a maximum current through clamping diodes somewhere about 1-2mA.
