9.2.2.2 Setting Fall Time for Shutdown Power Sequencing

Microcontrollers and processors often have a specific shutdown sequence in which power must be removed. Using the adjustable Quick Output Discharge function of the TPS22919 device, adding a load switch to each power rail can be used to manage the power down sequencing. To determine the QOD values for each load switch, first confirm the power down order of the device you wish to power sequence. Be sure to check if there are voltage or timing margins that must be maintained during power down.

Once the required fall time is determined, the maximum external discharge resistance (R_DIS) value can be found using Equation 2:

Equation 1 can then be used to calculate the R_QOD resistance needed to achieve a particular discharge value:

To ensure a fall time greater than, choose an R_QOD value greater than 600 Ω.