Electronic – MSP430 ADC overvoltage


The maximum input voltage of a MSP430 is Vcc+0.3V. What is the result of the ADC if I provide Vcc+0.3V as input? Is the digital output of the ADC just the maximal value?

Best Answer

The \$V_{CC} + 0.3V\$ is Absolute Maximum Ratings. It's an often made error, but you're never supposed to operate your device under these conditions. Even if the numbers suggest that these are acceptable values, continuous operation at those values may damage the device.
That said, most types of ADC, including MSP430 sigma-delta, will give a maximum reading if the input voltage is higher than the reference. The reason is that the ADC will compare a voltage derived from the reference (either through integration, like in sigma-delta, or through charge redistribution, like in SA) against the input voltage, and since this will be higher than the reference this voltage will never reach the input's level.

It's good design practice to have a keen eye for such maximums. If you know that the input voltage may go higher than the ADC reference, you better scale it down a bit using a voltage divider. Not only do you prevent damage, but you'll also be sure to be able to measure over the full range. If the reference voltage is 3.6V, then an input voltage of 3.6V and one of 3.7V would give you the same reading, but you won't be any wiser.