Hi Team,
In one of my project we are using ADC128D818. My supply voltage and reference voltage is 5VDC.
Condition:
We didn't give any input signal, Some time we observed 5VDC on all input signal (All inputs are in float)
Please let me know what will be the issue. Please find the Schematic below.
Thanks Ashok
Ashok,
If you are just using a multimeter to measure from the INx pin to ground then you may see a 5VDC signal. It may depend on the leakage seen at the pin.
If you look at the input structure for the ADC, you would find a set of input protection diodes that look like this:
With any of these structures, there may be some leakage. If the input leakage is sourced from the diode structure from V+, this may cause the voltage at the pin to go to the positive supply. Note that this leakage current is typically 5nA. If you think the current sourced from the pin is significantly higher, there may be some damage of the ESD structures if the pin has been over-voltaged. This may cause extra leakage current from the pin.
Has this voltage interfered with any measurements you've made with this board? It's possible this voltage could be some other effect, but this is one possible source.
Joseph Wu
