The GPIO pin I want to use as ADC input is 5V-tolerant - LPC1765FBD100

[KSB]

I am using LPC1765FBD100 microcontroller for one of my existing design. In that, I have used pin # 6 {P0[26]/AD0[3]/AOUT/RXD3} as a digital input pin with 5V pullup for one digital sensor. Now we would like to replace the digital sensor with some analog circuitry to solve some field issues.

As we know, for ADC 0 - 3.3V is the range. So planned to implement a resistor divider network to reduce the voltage to 3.3V. But in our design, the resistor divider top resistor is on the main board (Board#1) and the bottom resistor is on the daughter board (Board#2). When we connect both boards, the ADC pin will get 0V to 3.3V. If the daughter board(Board#2) is not connected, microcontroller pin# 6 will get the 5V through 1K pullup because divider networks resistors are in two different boards. My question is, will this 5V create any damage when we apply 5V through 1K resistor for the ADC pin? 

Please advise, ADC pin is 5V tolerant or 3.3V

[KSB]

Hi Miguel,

Thanks for your reply. Yes VDD is 3.3V.

My question is when we apply +5V to ADC pin (pin # 6), will it create any damage?

According to datasheet, "  When configured as a ADC input, digital section of the pad is disabled and the pin is not 5 V tolerant". 
Request you to read my query once again, Please let me know if you have any question.

[Miguel04]

Hi @KSB 

Sorry for the misunderstanding, I will need more information. When you have the 5V, the board is running or it is in reset mode. If it is in reset mode, the pins are default configurated as GPIO so it will not cause harm, if it is runnning, the pin will be configurated as ADC and the maximun voltage is going to be 3.3 V and it could burn the board, it depends on how de the vdd is in that moment. 

Let me know if this answer your question. 

Best Regards, Miguel.

[Miguel04]

Hi @KSB 

According to the LPC1765 product data sheet and user manual, the ADC electrical characteristics says that the maximum voltage is VDD = 3.3 V. 

Let me know if you have another question.

Best Regards, Miguel.