topic Gentle Backdrive on LPC17xx GPIO okay? in LPC Microcontrollers https://community.nxp.com/t5/LPC-Microcontrollers/Gentle-Backdrive-on-LPC17xx-GPIO-okay/m-p/524889#M7525 <HTML><HEAD></HEAD><BODY><STRONG>Content originally posted in LPCWare by Adam.Garrison on Tue Feb 23 11:24:57 MST 2016</STRONG><BR /><SPAN>I am looking at the most recent rev of our board and have a question about the inputs on the processor.</SPAN><BR /><SPAN> </SPAN><BR /><SPAN>Currently we are using a button to power the processer, effectively this pin drives the shutdown pin on our 3.3V regulator. Our charger circuit has a couple inputs/outputs that are fed into the processor for either status or control.</SPAN><BR /><SPAN> </SPAN><BR /><SPAN>One of the controls the processor can provide is how much current our charger can draw off of USB charging.&nbsp; I currently have a pull up on that pin to Vbus (5V).&nbsp; This trace runs from the charger to a pin on the processor which is an output.&nbsp; In the field I suspect that customers will use the USB Micro B port for charging to keep the battery topped off.&nbsp; The problem I see is this….when they are plugged into USB, but the unit is not turned on, there is 5V on the pin to the processor (through a 10k resistor) which is effectively 500uA of current flowing into that pin.</SPAN><BR /><SPAN> </SPAN><BR /><SPAN>I checked the power pins on the processor and none of them show any voltage at all (&nbsp; I was worried about it backpowering the core through the GPIO pins).&nbsp; The LPC1778 says that it is 5V tolerant when the core is powered.</SPAN><BR /><SPAN> </SPAN><BR /><SPAN>If I limit the current like this, am I okay doing this with such a small amount of current flowing through it?</SPAN><BR /></BODY></HTML> Wed, 15 Jun 2016 18:10:30 GMT lpcware 2016-06-15T18:10:30Z Gentle Backdrive on LPC17xx GPIO okay? https://community.nxp.com/t5/LPC-Microcontrollers/Gentle-Backdrive-on-LPC17xx-GPIO-okay/m-p/524889#M7525 <HTML><HEAD></HEAD><BODY><STRONG>Content originally posted in LPCWare by Adam.Garrison on Tue Feb 23 11:24:57 MST 2016</STRONG><BR /><SPAN>I am looking at the most recent rev of our board and have a question about the inputs on the processor.</SPAN><BR /><SPAN> </SPAN><BR /><SPAN>Currently we are using a button to power the processer, effectively this pin drives the shutdown pin on our 3.3V regulator. Our charger circuit has a couple inputs/outputs that are fed into the processor for either status or control.</SPAN><BR /><SPAN> </SPAN><BR /><SPAN>One of the controls the processor can provide is how much current our charger can draw off of USB charging.&nbsp; I currently have a pull up on that pin to Vbus (5V).&nbsp; This trace runs from the charger to a pin on the processor which is an output.&nbsp; In the field I suspect that customers will use the USB Micro B port for charging to keep the battery topped off.&nbsp; The problem I see is this….when they are plugged into USB, but the unit is not turned on, there is 5V on the pin to the processor (through a 10k resistor) which is effectively 500uA of current flowing into that pin.</SPAN><BR /><SPAN> </SPAN><BR /><SPAN>I checked the power pins on the processor and none of them show any voltage at all (&nbsp; I was worried about it backpowering the core through the GPIO pins).&nbsp; The LPC1778 says that it is 5V tolerant when the core is powered.</SPAN><BR /><SPAN> </SPAN><BR /><SPAN>If I limit the current like this, am I okay doing this with such a small amount of current flowing through it?</SPAN><BR /></BODY></HTML> Wed, 15 Jun 2016 18:10:30 GMT https://community.nxp.com/t5/LPC-Microcontrollers/Gentle-Backdrive-on-LPC17xx-GPIO-okay/m-p/524889#M7525 lpcware 2016-06-15T18:10:30Z