Power Stage Current-Sense Accuracy Improvement
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Solution Overview
Problem
Existing power stage current-sense methods in information handling systems face accuracy issues due to noise from high- and low-side FET switching, leading to undue throttling, excessive ripple in output voltage, and unexpected fault conditions, especially as current demands increase.
Innovation Solution
The implementation of a method that estimates low-side current levels by detecting current levels at different times during the switching cycle, using a blanking time and an additional sense time to improve accuracy, and calculating peak current values based on these measurements, without relying on external resistors for inductance indication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional current sensing methods are used during FET switching, then the system can detect current levels, but noise from high- and low-side FET switching degrades measurement precision
Solution Approach 1:
The current sensing measurement is divided into multiple discrete time points during the switching cycle. Instead of taking a single measurement that captures noise, the system segments the measurement into specific intervals (first time point during dead time, second and third time points during switch conduction) to isolate and eliminate noisy portions of the waveform.
Solution Approach 2:
The system performs preliminary current measurements at strategically chosen time points before the noisy FET switching events occur. By measuring at the first time point during the dead time period before the high-side FET switches on, the system captures current information before noise is introduced, then uses these preliminary measurements as a basis for calculating accurate current values.
2Productivity
If current measurements are taken during active switching, then real-time current information is obtained, but undue throttling and excessive ripple occur due to inaccurate sensing
Solution Approach 1:
The system implements a feedback mechanism where current measurements taken at specific time points are used to calculate accurate instantaneous and peak current values. These calculated values feed back into the control loop to regulate the switching duty cycle, ensuring that real-time current information is obtained without the instability and throttling issues caused by noisy traditional sensing methods.
3Ease of manufacture
If external resistors are used for inductance indication, then current sensing can be implemented, but device complexity and cost increase
Solution Approach 1:
The system uses the existing low-side FET and its inherent on-resistance as the sensing element, eliminating the need for external current sensing resistors. The current measurements are taken across the low-side FET during specific time periods, and the controller uses these measurements along with knowledge of the FET's on-resistance to calculate current values, making the system self-sufficient without additional external components.
Data Source
AI summary
A power stage includes a power converter having high- and low-side switches, a driver circuit that drives the switching power converter based upon a PWM signal, and a current sensing circuit that detects a low-side current level on the low-side switch, and provides a current level signal that includes the low-side current level. The power stage turns on the low-side switch at a first time, and estimates a first low-side current level at the first time. In estimating the first low-side current level, the power stage detects a second low-side current level at a second time while the low-side switch is turned on, the second time being after the first time, and detects a third low-side current level at a third time while the low-side switch is turned on, wherein the third time is after the second time. The first low-side current level is estimated based upon the second and third low-side current levels.