Other Parts Discussed in Thread: SN74CBTLV1G125
I'm confused about the ESD structure and the usage of GPIOs and the Ref+ Input, when the device is unpowered. I'm referring to the device datasheet as of June 2014
The Maximum ratings (Table 32-1) state:
VIN_GPIO | Input voltage | -0.3 | 4 | V
Table 32-7. "Recommended FAST GPIO Pad Operating Conditions":
VIH | Fast GPIO high-level input voltage | 0.65 * VDD | - | 4 | V
Both specifications are independent of VDD, thus no clamping diode to VDD can be assumed.
But Table 32-37. "Non-Power I/O Pad Voltage/Current Characteristics" states
VIO | IO pad voltage limits if voltage protected | -0.3 | VDD | VDD+0.3 | V
This specification is consistent with figure 32-17. "ESD Protection for Non-Power Pins (Except WAKE Signal)", but in contrast to the other two tables.
Could somebody clarify the issue?
I have to provide an external 3.3V reference voltage to the device. Are there any recommendations how to do it?