Multiphase Converter Phase Activation Sequence
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Solution Overview
Problem
Multiphase DC-DC converters face challenges in transient response and current sharing due to phase shedding and load changes, leading to inductor saturation and voltage ripple, especially when phases are added or removed based on the Power State Indicator (PSI) signal, and existing current sensing techniques are temperature-dependent.
Innovation Solution
The solution involves ensuring the high side switch is always turned on before the low side switch during phase activation, utilizing a preset delay in phase shedding based on the PSI signal, and employing a thermally compensated current sensing method using a negative temperature coefficient (NTC) thermistor to correct for temperature changes in inductor direct current resistance (DCR), providing accurate current information referenced to a remote Kelvin ground.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the low side switch is turned on before the high side switch during phase activation, then the phase can be activated, but this causes current perturbation and poor transient response
Solution Approach 1:
The high side switch is turned on before the low side switch during phase activation. This preliminary action ensures that the phase is properly prepared before current flow begins, preventing current perturbation and maintaining reliable transient response.
2Loss of energy
If phases are shed during light load condition to reduce switching losses, then efficiency is improved, but current loop perturbations occur and transient response deteriorates
Solution Approach 1:
A preset delay is implemented before shedding phases during light load conditions. This delay allows the system to stabilize before transitioning to fewer phases, preventing current loop perturbations and maintaining transient response performance while still achieving efficiency improvements.
3Use of energy by moving object
If the number of phases is changed based on PSI signal to match load requirements, then power efficiency is improved, but loop bandwidth changes causing poor transient response
Solution Approach 1:
A preset delay is introduced when changing the number of phases in response to PSI signal. This preliminary delay allows the system to prepare for the transition, maintaining stable loop bandwidth and preventing transient response deterioration while still achieving power efficiency improvements through dynamic phase adjustment.
4Loss of information
If current sensing is performed using inductor DCR, then current information is obtained, but the measurement is temperature-dependent and inaccurate
Solution Approach 1:
The system compensates for temperature-dependent inductor DCR variations by adjusting the current sensing parameters. This allows accurate current information to be obtained despite changes in temperature, eliminating the measurement inaccuracies caused by thermal effects.
5Productivity
If disabled phases are added back with zero inductor current, then the converter can handle increased load, but the added phase sinks current causing inductor saturation
Solution Approach 1:
The high side switch is turned on before the low side switch when adding disabled phases back into service. This preliminary action prevents the added phase from sinking current and causing inductor saturation, while still enabling the converter to handle increased load requirements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach minimizes current perturbations, reduces inductor saturation, and improves transient response by maintaining low output impedance, while providing accurate and temperature-compensated current information, thus enhancing the efficiency and stability of the converter.
Implementation Method 1
employing a thermally compensated current sensing method using a negative temperature coefficient (NTC) thermistor to correct for temperature changes in inductor direct current resistance (DCR)
Data Source
AI summary
A multiphase converter comprising a plurality of converter circuits, each converter circuit having series connected high and low side switches connected across a voltage bus with a common node provided therebetween, each of the common nodes connected through a respective inductor to an output node of the converter coupled to a load, the high and low side switches each being controlled by a control circuit to provide a desired output voltage at the output node, the control circuit including a first circuit for disabling and enabling at least one phase in response to a condition of the load, the circuit causing the high side switch to be turned on prior to the lower side switch when a disabled phase is enabled.