What is the maximum current through clamping diodes in nRF51822?

RE: What is the maximum current through clamping diodes in nRF51822?

Nikita — Sat, 18 Jan 2014 13:51:37 GMT

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.

RE: What is the maximum current through clamping diodes in nRF51822?

Nikita — Sat, 18 Jan 2014 07:36:03 GMT

I think in my case I can make protection like this so I don't need internal clamping diode. But it'll still be useful for the future to know what is the maximum current through clamping diodes in nRF51822.

RE: What is the maximum current through clamping diodes in nRF51822?

Nikita — Fri, 17 Jan 2014 18:22:55 GMT

I think I should consider additional protection of digital power supply from appearing 24 V at Point_1 using diode.

RE: What is the maximum current through clamping diodes in nRF51822?

Nikita — Fri, 17 Jan 2014 15:00:58 GMT

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.

RE: What is the maximum current through clamping diodes in nRF51822?

Stefan Birnir Sverrisson — Fri, 17 Jan 2014 13:16:44 GMT

Hi Nikita

If you intend to use the ADC with voltage from an input source then you should read this thread in order to realize the voltage limitations: http://devzone.nordicsemi.com/index.php/what-voltage-range-can-be-measured-with-the-adc#reply-103

You should also read this thread on considerations for a voltage divider on a ADC input: https://devzone.nordicsemi.com/index.php/adc-reference-selection-nrf51822#reply-3547

Here is a voltage divider suggestion for a Lithium battery: http://devzone.nordicsemi.com/index.php/how-to-measure-lithium-battery-voltage and http://devzone.nordicsemi.com/index.php/what-s-wrong-with-measuring-lithium-battery-voltage#reply-1576

Here you can realize the internal ADC circuit model: http://devzone.nordicsemi.com/index.php/analog-prescale-question

For ADC considerations when using with BLE softdevice: http://devzone.nordicsemi.com/index.php/adc-softdevice-sample-rate-on-nrf51822#reply-1791