Current-Mode Controlled DC-DC Regulators (Part 4): Small-Signal Behavior Of The CC Loop

by Timothy Hegarty, Texas Instruments, Phoenix, Ariz., How2Power Today, Oct 15 2025

Focus:
In part 3 of this series, the author defined a CC-CV regulator with a novel dual-loop architecture activating either the CC or CV error amplifier at a given time, thus minimizing loop interactions and yielding a seamless handoff between CC and CV. He then described a synchronous buck controller with this CC-CV implementation that offers accurate current-regulation performance, a low component count and reduced cost. This fourth installment builds on part 3 by pursuing the relevant small-signal transfer functions for the CC loop. Designing the CC and CV loops with similar small-signal dynamics enables the use of a shared compensation component network. Bode plot simulations of the loop response in CC mode, based on a commercially available CC-CV GaN synchronous buck converter (the LMG708B0), illustrate the small-signal characteristics of the dual- loop architecture.

What you’ll learn:

• How to derive the CC loop transfer function for the CC-CV regulator with novel dual-loop architecture (LM5190-Q1 or LMG708B0)
• How to validate the theoretical analysis of the CC loop with a SIMPLIS simulation of an LMG708B0-based buck converter

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