SIMO DC-DC Converter With Shared Bootstrap Gate Drive
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Solution Overview
Problem
Conventional single inductor multiple-output (SIMO) DC-DC converters require multiple off-chip bootstrap capacitors and pins to regulate multiple output voltages, leading to a costly and complex design due to the need for high gate-source voltages in n-type transistor switches, which increases the on-resistance and power efficiency challenges.
Innovation Solution
A DC-DC converter design that utilizes a shared off-chip bootstrap capacitor among multiple outputs, where the bootstrap capacitor is connected between the inductor and each output switch, allowing for efficient conversion of input voltage to output voltages by turning on output switches through a bootstrap voltage, reducing the need for multiple capacitors and pins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple off-chip bootstrap capacitors are used to regulate multiple output voltages, then the output voltage regulation is improved, but the device complexity and cost increase
Solution Approach 1:
The patent merges multiple separate bootstrap capacitors into a single shared bootstrap capacitor that serves all output voltages. The bootstrap capacitor is connected to a common node that distributes the bootstrap voltage to multiple N-type transistor switches through individual bootstrap diodes, eliminating the need for multiple capacitors and reducing pin requirements.
Solution Approach 2:
The single bootstrap capacitor performs multiple functions by providing bootstrap voltage to all N-type transistor switches in the circuit. It universally supports the gate-drive requirements of multiple output stages, allowing one component to replace what would traditionally require N separate components.
2Loss of energy
If N-type transistor switches are used to reduce on-resistance, then the power efficiency is improved, but the requirement for higher gate-source voltages increases device complexity
Solution Approach 1:
The bootstrap circuit uses the output voltage itself to generate the required gate-source voltage for the N-type transistor switches. During the switch off-period, the bootstrap capacitor charges to the output voltage level, and during the on-period, this stored voltage is applied to the gate, automatically providing the necessary drive voltage without external intervention.
Solution Approach 2:
The bootstrap capacitor charges and discharges in periodic cycles synchronized with the switching operation. It charges when the switch is off and discharges to provide gate drive when the switch is on, creating a self-sustaining periodic voltage supply that enables continuous operation of the N-type transistors.
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 design reduces the number of required capacitors and pins, lowering the overall cost and complexity while maintaining efficient power conversion with minimal ripple in output voltages, thus addressing the inefficiencies and cost issues of conventional SIMO converters.
Implementation Method 1
An inductor may be configured to be charged by applying the input voltage to the inductor. An inductor may operate as a current storage element that transfers energy from input voltage to output voltages.
Implementation Method 2
The plurality of output capacitors may maintain the plurality of output voltages. Each of the plurality of output capacitors may be needed as a voltage storage element that maintains an output voltage.
Implementation Method 3
An output bootstrap capacitor may be connected between the inductor and each of the plurality of output switches. An exemplary output bootstrap capacitor may be configured to convert the input voltage to an nth output voltage.
Data Source
AI summary
A direct current (DC)-DC converter for converting an input voltage to a plurality of output voltages. The DC-DC converter includes an inductor, a plurality of output capacitors, a plurality of output switches, and a bootstrap capacitor. The inductor is configured to be charged by applying the input voltage to the inductor. Each of the plurality of output switches is connected between the inductor and a respective output capacitor of the plurality of output capacitors. The bootstrap capacitor is connected between the inductor and each of the plurality of output switches. The bootstrap capacitor is configured to convert the input voltage to an nth output voltage of the plurality of output voltages. The input voltage is converted to the nth output voltage by coupling the inductor to an nth output capacitor of the plurality of output capacitors through an nth output switch of the plurality of output switches.