Fuse-less Self-Start Controller for DC-DC Converters
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Solution Overview
Problem
Voltage regulators, such as fully integrated voltage regulators (FIVR) or other DC-DC converters, face challenges in generating a supply output during system startup without access to fuse information, which is necessary for traditional steady-state controllers, leading to inefficiencies and increased costs due to the need for additional resources and complex compensation circuits.
Innovation Solution
A fuse-less self-start controller is implemented, using a relaxation oscillator to set the switching frequency of the buck converter and a simple output feedback network to maintain output voltage above the set point, eliminating the need for PVT trims and allowing for minimal voltage and inrush current overshoots, even in advanced process technology nodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional steady-state controllers are used during startup, then fuse information can be utilized for control, but the controller cannot generate supply output when fuse information is unavailable
Solution Approach 1:
The controller dynamically adapts its operation mode based on the availability of fuse information. During startup before fuse download, it operates in open-loop mode with predetermined parameters. After fuse download completes, it transitions to closed-loop mode using fuse information for optimized control. This dynamic mode switching enables the controller to function reliably in both startup and steady-state conditions without requiring fuse information to be available at all times.
2Adaptability or versatility
If complex compensation circuits are added to handle startup without fuses, then startup capability is improved, but device complexity and cost increase
Solution Approach 1:
The control functionality is segmented into distinct operational phases: open-loop startup phase using predetermined parameters stored in non-volatile memory, and closed-loop steady-state phase using fuse information. This segmentation allows the controller to handle startup without fuses using simple predetermined parameters, avoiding the need for complex compensation circuits while maintaining full operational capability.
3Measurement precision
If PVT trims are used to maintain output accuracy, then output precision is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The controller performs self-adjustment during operation by monitoring output voltage and automatically correcting deviations from the target voltage. The open-loop startup sequence is designed to naturally settle the output voltage close to the set point, and the subsequent closed-loop operation maintains precision without requiring external PVT trim adjustments. This self-service approach eliminates the need for complex trim circuits while maintaining output accuracy across process, voltage, and temperature variations.
4Reliability
If additional resources are allocated for startup control without fuses, then startup reliability is improved, but resource usage and cost increase
Solution Approach 1:
The controller uses a single unified architecture that handles both startup and steady-state operation. The same control circuitry, output stage, and monitoring functions are used in both open-loop startup mode and closed-loop steady-state mode. This multi-functional design eliminates the need for separate dedicated startup circuits, reducing overall resource usage while maintaining reliable startup capability.
Data Source
AI summary
A digital self-start controller, which is functional without fuse and/or trim information. The self-start controller protects a DC-DC converter against large inrush currents and voltage overshoots, while being capable of following a variable VID (voltage identification) reference ramp imposed by the system. The self-start controller uses a relaxation oscillator to set the switching frequency of the DC-DC converter. The oscillator can be initialized using either a clock or current reference to be close to a desired operating frequency. The output of the DC-DC converter is coupled weakly to the oscillator to set the duty cycle for closed loop operation. The controller is naturally biased such that the output supply voltage is always slightly higher than a set point, eliminating the need for any process, voltage, and/or temperature (PVT) imposed trims.