Soft Start Circuitry for High Power Charge Pumps
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High power charge pumps face issues during start-up due to very high currents generated in switching transistors and capacitors, leading to over-voltages that can damage connected loads, as they lack inductors to limit these currents and store energy, and existing start-up techniques either produce high currents for short durations or result in high power dissipation and temperature issues.
Innovation Solution
A method for soft starting high power charge pumps by slowly ramping up bootstrap supply voltages and gate-to-source voltages of power transistors, limiting current and voltage during start-up, and distributing power dissipation across multiple transistors instead of a single LDO pass device, allowing for controlled charging and reduced peak currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high power charge pumps charge capacitors from initial condition voltages to steady state voltages, then the charge pump provides operating voltages for portable electronic devices, but very high currents are generated in switching transistors and capacitors causing over-voltages that can damage connected loads
Solution Approach 1:
The patent applies preliminary action by pre-charging bootstrap capacitors to specific voltages before enabling power transistor switching. The method sets initial voltage conditions on bootstrap capacitors (CB1, CB2) to predetermined levels (VDD and VDD/2) before start-up, which establishes safe operating conditions for the power transistors during the charging process, preventing excessive currents and over-voltages that would otherwise damage connected loads.
2Productivity
If existing start-up techniques are used to charge capacitors quickly, then charging speed is improved, but very high currents are generated for short durations causing power dissipation and temperature issues
Solution Approach 1:
The patent applies dynamics by implementing a two-phase charging strategy that transitions from a controlled initial phase to a full-power phase. During the initial phase, bootstrap capacitors are charged to predetermined voltages with limited current. Once these initial conditions are established, the charge pump transitions to normal operation with full switching capability. This dynamic approach enables fast charging while avoiding excessive power dissipation and temperature issues during the start-up transient.
Data Source
AI summary
A method to soft start a charge pump circuit according to embodiments includes enabling switching for a plurality of power transistors, selecting a first switching control signal from a plurality of switching control signals for the selected plurality of power transistors, slowly ramping up a plurality of bootstrap supply voltages associated with the selected plurality of power transistors, driving a gate-to-source voltage of each power transistor of the selected plurality of power transistors at a first predefined level, and determining if the plurality of bootstrap supply voltages are less than a second predefined level. If the plurality of bootstrap supply voltages are less than the second predefined level, the method further includes toggling and thereby selecting a second switching control signal from the plurality of switching control signals for a second selected plurality of power transistors.