Digital Feedback Controls Supply Voltage Accurately

by Simon Bramble, Field Application Engineer, and Paul Holden, Member of Technical Staff, Maxim Integrated Products, Sunnyvale, Calif., Power Electronics Technology, Jan 01 2006

Focus:
Adding a digital feedback loop to a buck regulator enables digital programming of the regulator's output voltage, improves load regulation, and corrects for voltage offset and drift. In the design described here, a stepdown regulator with adjustable 1.25-V to 5.5-V, 600-mA output is controlled using a digital feedback loop consisting of an 8051-compatible microcontroller (MCU), a 12-bit DAC, a 12-bit ADC, and an external 5-V reference. A serial transceiver provides communication between the MCU and a PC. The design of the analog and digital circuits, pc board layout, and firmware is explained, and software and firmware files are made available. Performance results are shown. Tips are given on how to custom the design for different output voltage ranges, how to slow down the feedback loop to avoid overshoot and undershoot, and how to speed up the feedback for faster transient response.

What you’ll learn:

• How to design a digital feedback loop to control the output voltage of an adjustable dc-dc converter
• How to design a digital feedback loop to improve output voltage regulation and accuracy of an adjustable dc-dc converter

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