lpcware

port direction change to output causes current spike

Discussion created by lpcware Employee on Jun 15, 2016
Latest reply on Jun 15, 2016 by lpcware
Content originally posted in LPCWare by mspahr on Fri Apr 11 12:20:46 MST 2014
Port direction change causes current spike.

LPC11U35FET48/501

When P0,22 direction is changed to output, there is a large current spike
on VCC.  It sags my 3.3V VCC supply to 3V.  It is less than 1uS in duration.
It then takes my 25mA power supply 100uS to fully recover.
The processor is normally running about 11mA so I am guessing it spikes to
greater than 25mA.
None of the other 11 GPIOs that are set to outputs do this.
P0,22 has a 5K resistor to ground and a small FET gate.
Before the direction change, the IOCON is set to 0x80 (set to GPIO, no pull-up).
The data register is set to 0.
I have scoped the P0,22 at the time of the direction change and it is always
low, before, during, and after the direction change.
I can subsequently set P0,22 high and low and it causes no current spike.
This has been seen on multiple boards so it is not just a bad chip.

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