This application note uses a typical image sensor to assess three feasible power solutions that need to support the sensor's power sequence requirements. These requirements can be found in the sensor data sheet. Figure 1-1 demonstrates the power up sequence requirement of a typical image sensor. AVDD 2.8 V must power up first, followed by DOVDD 1.8 V, and then DVDD 1.2 V.

Figure 1-2 is the power down sequence requirement of the image sensor. The sequence is the reverse order of the power up sequence: DVDD 1.2 V, followed by DOVDD 1.8 V, and lastly AVDD 2.8 V.

Achieving the power up sequence is often a straightforward process. The bigger design challenge is reversing this sequence to meet the power down requirements. The following sections discuss this challenge in the context of three common power solutions for image sensors. These solutions consist of:

1. A discrete solution using regulator power good and enable pins.
2. A discrete solution using a voltage supervisor.
3. A Power Management Integrated Circuit (PMIC) using built-in, programmable power sequencing.