How to read datasheets
What does it mean when a datasheet describes an input pin as "5 V tolerant"?
- AThe device is guaranteed to operate with the same performance whether the supply voltage is 5 V or 3.3 V
- BThe pin can output a 5 V high-level signal
- CEven when the device runs from a supply such as 3.3 V, a 5 V signal may be applied to that input
Show answer and explanation
Answer: C. Even when the device runs from a supply such as 3.3 V, a 5 V signal may be applied to that input
A normal CMOS input has an ESD protection diode to the supply (VDD), and if the input exceeds about VDD + 0.3 V, the diode conducts and current flows in. A 5 V tolerant input is designed without this path, so applying 5 V while the supply is 3.3 V causes neither damage nor current inflow. It only tolerates the input; it does not mean the output reaches 5 V. Whether 5 V may also be applied while the supply is off must be checked in a separate statement.