Modern power systems requiring a variety of voltages
Different voltage domains must be properly controlled
High-reliability power-up/down sequences become increasingly important


Today's electronic applications do not require just a single power supply voltage, such as 5 V or 3.3 V. It is not uncommon to require as many as 10, 20, or even more voltages.

Furthermore, the same voltage may need to be generated in different domains. The same two voltages may need to be provided for analog loads and digital loads. This separation has the advantage of preventing mutual interference and providing energy to different loads at different times.

Figure 1 is a system block diagram that requires multiple voltage domains. These voltages are generated using individual switching regulators and linear regulators. The selection of each voltage converter can vary depending on the required conversion efficiency, the voltage to be generated, and the current consumed by the load. Therefore, each voltage converter design can vary significantly.

The delay time required for each voltage to reach the desired level may vary from converter to converter. Failure to properly control the ramping of different voltage domains can result in functional problems and damage to the system. A reliable power-up sequence is required to ensure that each voltage reaches the desired value at the desired time. A specific power-down sequence may also be required during shutdown.

In systems that use multiple power supply voltages, it is also important to monitor the different voltages. In systems that use two voltage domains, this is simple, but when using multiple voltages, the task becomes much more complex. For this reason, many sequencer devices include a supervisory or voltage monitoring function.

Figure 2 shows the ADM1186-1 analog sequencer IC. This device can control and monitor four voltage domains. The voltages can be powered up and down by controlling the enable (on/off) pin of the voltage converter, and the turn-on time of the voltage converter can be adjusted by delaying it using a small capacitor.

The output voltage can also be monitored via the monitoring pin. Once all voltages have been built up, the sequencer circuit generates a power-good signal.

Analog sequencing solutions such as the ADM1186-1 are easy to use. The device supports all the functions required for systems that use multiple voltages. Its design is simpler than that of a digital sequencer, and therefore requires less digital monitoring functions. This means that there is no need for PMBus or similar protocols.

Figure 1 The system uses eight voltage domains. So how do you implement sequencing and monitoring in a system that uses more than four voltage domains? In this case, you can combine multiple ADM1186-1 circuits. The ADM1186-1 sequencer can connect any number of products.

There are many examples of sequencing types that combine individual sequencers in the market. However, what makes the ADM1186-1 different from them is that it can fully support sequencing during power-up as well as power-down in connected applications, as shown in Figure 3.

Competitive solutions only allow multiple sequencer ICs to be connected and their individual voltages to be raised in a controlled manner, but do not support power-down sequencing in this daisy-chain configuration. Reliable power-up and power-down sequencing is critical for modern systems. The ADM1186-1 provides flexible implementation of this type of sequencing, reducing development effort.

Meanwhile, ADI provides various information on sequencing (△ Overview of Analog Sequencers △ Overview of Digital Sequencers △ Understanding Power System Management △ Power Sequencing to Prevent System Damage ).



This article is a summary of the article titled “A Reliable Power-Up and Power-Down Sequence” by Frederik Dostal, Power Management FAE at Analog Devices.