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?
Thanks for this information, it's quite useful, especially about ADC input resistance. But it seems you have not quite understood what I meant. I want to make a circuit which is presented on the attached image. I will use 1/3 ADC prescaling. Thermistor RK1 will be outside of the device and connected to it via a cable. This cable besides RK1 wires has 24V supply wires. In some emergency case of damaging this cable, 24V may be connected to the ADC input. So I want to protect ADC input from 24V through current limiting resistor R2 that will limit current through clamping diode in the nRF51822 pin. To calculate required value of resistor R2 I need to know maximum current through clamping diodes in nRF51822 GPIO pins.
Thanks for this information, it's quite useful, especially about ADC input resistance. But it seems you have not quite understood what I meant. I want to make a circuit which is presented on the attached image. I will use 1/3 ADC prescaling. Thermistor RK1 will be outside of the device and connected to it via a cable. This cable besides RK1 wires has 24V supply wires. In some emergency case of damaging this cable, 24V may be connected to the ADC input. So I want to protect ADC input from 24V through current limiting resistor R2 that will limit current through clamping diode in the nRF51822 pin. To calculate required value of resistor R2 I need to know maximum current through clamping diodes in nRF51822 GPIO pins.
