Multiphase Converter PFM Pulse Rotation for Low-Ripple Light Loads
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Solution Overview
Problem
Current multiphase power converters face challenges in transitioning efficiently between pulse width modulation (PWM) and pulse frequency modulation (PFM) modes, particularly in minimizing output capacitance and ensuring extended battery life while maintaining high efficiency, especially in automotive applications where cost sensitivity is high.
Innovation Solution
The proposed solution involves a multiphase power converter system that includes a plurality of control logic circuits, a timer circuit, and a rotator circuit, which generate PFM pulses at different time periods based on output voltage amplitude and rotator signals, enabling the system to operate in both PWM and PFM modes. This configuration selectively enables current sense comparator circuits only during PFM pulse generation, reducing power consumption and output voltage ripple.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the multiphase power converter operates in PWM mode during light load conditions, then the output voltage regulation is maintained, but the power consumption increases and efficiency decreases
Solution Approach 1:
The system dynamically switches between PWM and PFM modes based on load conditions. During light load conditions, the controller transitions from PWM to PFM mode, where the switching frequency varies dynamically to maintain output voltage regulation while minimizing power consumption and maximizing efficiency
Solution Approach 2:
The system changes the operating mode parameter from fixed-frequency PWM to variable-frequency PFM. In PFM mode, the switching frequency is adjusted according to the load requirements, allowing the converter to operate at lower frequencies during light loads, thereby reducing power consumption and improving efficiency while maintaining proper output voltage regulation
2Quantity of substance
If the output capacitance is minimized to reduce cost, then the bill of materials cost decreases, but the output voltage ripple increases
Solution Approach 1:
The multiphase converter employs periodic interleaved switching of multiple phases, where each phase operates at a different time period. This periodic action with phase shifts causes the output voltage ripples from individual phases to cancel each other out, significantly reducing the overall output voltage ripple and allowing the use of minimized output capacitance
Solution Approach 2:
The system introduces asymmetric time period distribution among phases through the rotator circuit, where phases are deliberately staggered in their switching cycles. This asymmetric timing arrangement ensures that voltage ripple peaks from different phases do not align, achieving ripple cancellation with minimal output capacitance
3Measurement precision
If separate current sense comparators are used for PFM and PWM modes, then the measurement precision is improved, but the device complexity and silicon size increase
Solution Approach 1:
The current sense comparator circuit is designed with multi-functionality to serve both PFM and PWM modes. The same comparator hardware is reused across different operating modes by controlling its enable state through the rotator circuit and mode selection logic, thereby maintaining measurement precision while reducing device complexity and silicon area
Solution Approach 2:
The system merges the current sensing function for both PFM and PWM modes into a single shared comparator circuit. By combining the sensing resources and intelligently managing their utilization through control logic, the system achieves accurate current measurement for both modes without duplicating hardware, thus reducing overall device complexity
4Productivity
If all control logic circuits generate pulses simultaneously, then the productivity is maximized, but the output voltage ripple increases
Solution Approach 1:
The control logic circuits generate pulses in a periodic interleaved manner rather than simultaneously. Each phase has a designated time period with phase shifts, creating a periodic pattern where pulses are distributed across different time intervals. This maintains high overall productivity while the temporal distribution reduces peak current demands and output voltage ripple
Solution Approach 2:
The pulse generation process is segmented across multiple time periods and phases. Instead of all control logic circuits operating at once, the system divides the operation into sequential phases with distinct time windows, where each phase handles a portion of the total current demand. This segmentation maintains productivity while reducing ripple through distributed timing
Data Source
AI summary
A circuit includes a plurality of control logic circuits, each of the control logic circuits configured to provide respective pulses at different time periods. The circuit further includes a timer circuit configured to provide a timer signal to each of the control logic circuits based on an output voltage, wherein the timer signal determines a frequency of the respective pulses. Furthermore, the circuit includes a rotator circuit configured to provide a plurality of rotator signals to the control logic circuits, respectively, wherein each control logic circuit is configured to determine a time period of the different time periods during which to generate the respective pulses based on the respective rotator signal.