How to Implement a Simple Constant Current Regulation Scheme to a PCM Based Buck

Abstract

A buck converter is usually implemented as a constant voltage (CV) regulator. When the input voltage and load current change, the control loop adjusts the duty cycle to keep the output voltage constant.

However, more recently, many applications require regulation of both the output current and the output voltage. This is often refered to as constant current, constant voltage regulation (CC/CV). Typically, to implement CC/CV regulation, the designer needs to modify a CV regulation scheme adding circuitry to the feedback loop. This application note shows how to convert a peak current-mode (PCM) control scheme, configured as a CV regulator into a CC/CV regulator. The suggested approach herein can be applied to a controller, converter or module. Test results are also provided to demonstrate feasibilty.

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1 Introduction

Currently, there is a growing demand for CC/CV regulators in many applications, such as super capacitor energy backup, eBike GSM module and multi-cell battery stacks, USB power delivery, server BBU for 48 V bus architecture, and so on. However, buck regulators are typically implemented with CV regulation, therefore external circuitry is necessary to realize CC/CV regulation.

This application note provides a simple CC/CV configuration that can be added to most buck regulator products with PCM control, including controllers, converters and modules. Design principles and design considerations are discussed and test results are provided to show design implementation feasibilty.