Reliable Power Up and Power Down Sequence

Electronic applications often requires more than one supply voltage of 5V or 3.3V. Below is an example electronic system requiring eight voltages.


These voltages are generated by separate switching regulators and linear regulators. The choice of each voltage converter depends to a large extent on the required conversion efficiency, the voltage to be generated, and especially the current consumed by each load. As a result, the design of each voltage converter varies greatly. In addition, the delay of each rising voltage will be different for each converter. This leads to uncontrolled rises in different voltage domains, which can cause functional problems and damage the system. There will also be different delays of the individual voltages from each converter. This can also lead to uncontrolled rises in different voltage domains and the damage that comes from them.

Therefore a reliable power-up sequence is required to ensure that each voltage reaches its target value at the right time. Often, a specific power-down sequence must also be followed for shutdown.

In systems with multiple supply voltages, the ability to monitor these different voltages may be important. Sequencer devices which have a built-in supervisor or voltage monitoring function can help these systems.

One good example is the ADM1186-1 analog sequencer from ADI. It can control and monitor four voltage domains. Power-up and power-down of the voltages is performed through control of the enable (on/off) pins on the respective voltage converters. The turn-on times of the voltage converters can be adjusted by means of time delays using small capacitors. The respective output voltages are monitored via the corresponding monitor pins. When all voltages have been established, the sequencer circuit generates a power-good signal.

ADM1186-1 can also support complete sequencing during power-up, as well as power-down when
used in a linked application as below shown. Comparable solutions can offer the possibility of linking various sequencer ICs, but they only offer controlled ramp-up of the individual voltages, not controlled down-sequencing—that is, power-down of the voltages, in such a daisy-chain constellation.

1 Like