S/H in MSP432

As expected the S/H circuit in real life is more complicated than the simple circuit model we used earlier in the previous page. In the MSP432 manual, we learn that they use the following circuit to model the Sample/Hold and measure the sampling time.

As clear from the above figure the resistor, RI, and the two capacitors, CI and Cpint, are inside MSP432 and part of the sample and hold circuitry. Rs and Cpext on the other hand are the characteristics of the input such as joystick, accelerometer, etc. As for the first set, which are part of MSP432, the values are set and remain constant for each MSP432 chip. Since this information is device-specific, it can be found in the datasheet and not the user manual. For example, searching for the word Cpint, you can find the below table in the datasheet for the specific MSP432 on the Launchpad.

Given, the above values, tsample >> (14+1) * ln(2) * [(Rs + 1K) * 15p + Rs x (Cpext + 5p)]