Introduction

As the DC-DC Basic Knowledge “Application” edition, we begin with “Circuits to Implement Power Supply Sequences Using General-Purpose Power Supply ICs”.

Introduction

In ICs such as FPGAs and DSPs that have complex functions and require multiple power supplies, and electronic equipment requiring power supplies with multiple supply voltages, the order of power supply turn-on and turn-off is sometimes specified. If the stipulated order is not obeyed, not only may the system not startup up normally, but in some cases device failure may result.

The ordering of turn-on and turn-off of multiple power supplies is called a power supply sequence. The following is a schematic diagram of sequence control for three power supply systems.

One method to control a power supply sequence is to use a dedicated power supply sequence IC. There are also power supply ICs equipped with sequencing functions, and power supply ICs that have Power Good outputs and that can control sequencing. Using such products, sequencing circuits can be designed relatively easily; but in this article, a circuit examples are presented that implement power supply sequencing through general-purpose power supply ICs that have only output on/off (enable) functions and external circuits, without using a dedicated power supply sequence IC or a power supply IC provided with functions to support sequencing.

Two sequencing specifications are prepared as examples. For each specification, the configuration of the control block circuit, a circuit example, and an example of operation will be explained.