The DLPC34xx controller provides fail-safe I/O on all host interface signals (signals powered by VCC_INTF). This allows these inputs to externally be driven even when no I/O power is applied. Under this condition, the controller does not load the input signal nor draw excessive current that could degrade controller reliability. For example, the I2C bus from the host to other components is not affected by powering off VCC_INTF to the DLPC34xx controller. The allows additional devices on the I2C bus to be utilized even if the controller is not powered on. TI recommends weak pullup or pulldown resistors to avoid floating inputs for signals that feed back to the host.
If the I/O supply (VCC_INTF) powers off, but the core supply (VDD) remains on, then the corresponding input buffer may experience added leakage current; however, the added leakage current does not damage the DLPC34xx controller.
However, if VCC_INTF is powered and VDD is not powered, the controller may drives the IIC0_xx pins low which prevents communication on this I2C bus. Do not power up the VCC_INTF pin before powering up the VDD pin for any system that has additional slave devices on this bus.