PCA9306: PCA9306 EN and VREF2
Part Number: PCA9306
Why is there a FET from VREF1 to VREF2? It seems like that would always be a problem. We do not currently have a 200k series resistor on the VREF2 side and things seem to be working fine. This is in reference to this previous post: https://e2e.ti.com/support/interface/i2c/f/390/t/629454?tisearch=e2e-quicksearch&keymatch=PCA9306%20VREF2
Just to clarify, the FET between Vref1 and Vref2 is internal to the device.
The FET between Vref1 and Vref2 is meant to help establish a reference voltage for other circuitry in the device when Vref2 pin is shorted to Enable pin of the device. This is done to get lower propagation delays.
"We do not currently have a 200k series resistor on the VREF2 side and things seem to be working fine. "
If the FET is not turned on (Vref2<=Vref1+Vth) then the device will still function however if the FET is turned on then you basically have a very small impedance between Vref1 and Vref2 which can be simplified to a short circuit.
We are glad that we were able to resolve this issue, and will now proceed to close this thread.
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Do you have a diagram or schematic of how you connected it? We can give you better feedback once we know how you connected it in your system.
In reply to fhoude:
We have EN and VREF2 tied together and directly to 3.3V. 3.3V is always enabled.
VREF1 is tied to 1.8V which is powered up and down as needed.
In reply to Dan Markoff:
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