LPC1769 driving 5 V line

Discussion created by lpcware Employee on Jun 15, 2016
Latest reply on Jun 15, 2016 by lpcware
Content originally posted in LPCWare by inspire on Mon Apr 21 05:52:59 MST 2014

on a PCB I have the following scenario: an LPC1769 (3.3 Vdd) is connected to a signal line with 5 V through a 10 k resistor. The LPC has 5 V tolerant pins but I'm not sure if it can interact with the signal line correctly. The LPC can put a 0 V or a 3.3 V level on the sinal line. But what happens exactly?

a) In case of the 0 V level there will still be an input current of I = 5 V / 10k = 0.5 mA.
b) If the LPC puts a 3.3 V level to the signal line the 3.3 V will be pulled up with the 10 k resistor to above 3.3 V. Input current: I = (5V-3.3V)/10k = 0.17 mA

Is either of these cases a problem for the LPC? I'm afraid it might not withstand especially case b) for a long time, right? Is case a) also a problem?