Hi Alex,
Thanks for your devoting experiment.
And Could you check following my experiment ?
Phenomena and views.
1. I've supplied IOVDD = 1.8V and AVDD = 3.3V with Laboratory Power supply without LDO on circuit.
They are operating correctly. Because Laboratory Power Supplies have function of current sinking.
But normal LDO dose not have it. These have only sourcing function.
e.g. We use 1.8V LDO and external device supplies 2.2V to its output pin.
Then , voltage of the output pin of 1.8V LDO is 2.2V.
LDO can't down supplied voltage on its output pin.
2. I had external pull up resistor 1K ohm for i2c line. And pull up voltage is 3.3V.
This is reason for this issue. It changed with 10k ohm. And circuit operating correctly.
May be, this is only characteristic of internal structure of ADuCM.
Do Input protection diode of gpio pin is operating correctly ?
I think over voltage on gpio pin should flow to IOVDD , not other gpio pin.
I don't know exactly its internal structure.....
3. Thus , this issue closed. But one is remained.
When I use emulator , LPC2146 on emulator is using 3.3V supply voltage.
And it is driving ADuCM pin with 3.3V. Thus this issue is re-opened.
LPC2146's operating voltage must be above +3.0V from its datasheet.
Thus I can't change LDO on emulator.
Last solution : I have connected Lab power supply to IOVDD.
1.8V Lab suppy -> IOVDD pin and LDO output pin.
Gpio pins has 1.8V level correctly.
When I finished development, I should remove Lab power and
my circuit doesn't have any problem.
Could you check whether my experiments are correct or wrong ?