We're using a PCA9306 to level shift from a 3.3V master to a 1.8V slave. When we have the level shifter populated, the 1.8V rail increases to 2.3V. I've attached an image of the portion of the schematic with the PCA9306:
The 1.8V rail comes from the the 3.3V to 1.8V regulator. J2 is a jumper to select T_VCC to be 1.8 or 3.3 because we were originally going to drive the slave with 3.3V but we get better performance and power savings with 1.8V. U15, R31, and R32 are populated when we jumper pins 2 and 3 on J2 to make T_VCC 1.8V. We also remove R34 and R35 in this instance.
We've validated and tested all of the following (no I2C signals communication; just powering the IC):
1. 1.8V regulator outputs 1.8V when only the regulator and bypass caps are populated.
2. We also flipped VREF1 and VREF2 to be 3.3V and 1.8V but we still see 2.3V on the 1.8V rail.
3. We removed the R31 and R32 pull ups to the 3.3V rail and the 1.8V rail measures 1.8V but we need pull ups.
4. We put weak pull ups on R31 and R32 (10K), the 1.8V rail measures 2.3V.
Does anybody know what could be happening here and how to mitigate it? Thanks.
