Integrated Capacitor Network for Buck Converter Switch Node Ringing
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Solution Overview
Problem
High-frequency power supply modules with synchronous Buck converters experience unacceptable voltage ringing at the switch node due to parasitic inductances and capacitances, leading to potential damage and system reliability issues.
Innovation Solution
A capacitor network is integrated between the VIN and ground, physically adjacent to the Buck converter dies, to channel ringing energies away from the switch node, reducing parasitic inductance effects and effectively diverting oscillating energy to ground.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If synchronous Buck converter operates at high frequency (500 kHz to 1 MHz), then power delivery efficiency is improved, but voltage ringing at switch node increases due to parasitic inductances and capacitances
Solution Approach 1:
A capacitor network is introduced as an intermediary element between the switch node and ground. This capacitor network absorbs the oscillating energy exchanged between parasitic inductances and capacitances, acting as a mediator that dissipates the harmful ringing effects while allowing the high-frequency operation to continue efficiently.
Solution Approach 2:
The capacitor network converts the harmful voltage ringing into beneficial energy dissipation. By placing capacitors in parallel with the converter circuit, the oscillating energy that would otherwise damage components is redirected into the capacitor network, where it is safely dissipated through the equivalent series resistance of the capacitors.
2Ease of manufacture
If parasitic inductances from bonding wires and clips are present in the circuit, then device assembly is simplified, but switch node ringing amplitude increases to unacceptable levels (peak voltage about 25 V)
Solution Approach 1:
The capacitor network serves as an intermediary that decouples the harmful effects of parasitic inductances from the switch node. Instead of attempting to eliminate the parasitic inductances from the bonding wires and clips, the capacitor network absorbs their harmful effects, allowing the simplified assembly structure to be maintained while eliminating the ringing problem.
3Object-affected harmful factors
If capacitor network is integrated physically adjacent to Buck converter dies, then ringing energy is effectively channeled to ground, but device complexity increases
Solution Approach 1:
The capacitor network is merged with the existing converter structure by placing capacitors in parallel with the converter circuit and connecting them to the same power and ground nodes. This integration approach adds the necessary damping function without creating entirely new structural elements, thereby minimizing the increase in device complexity while achieving effective ringing suppression.
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
The solution achieves an 80% reduction in switch node ringing amplitude, ensuring reliable operation and preventing damage to the MOSFETs by effectively managing parasitic inductance and capacitance interactions.
Implementation Method 1
the exchange of energy between parasitic inductances mainly associated with the top clip at input node and the capacitance COSS across the sync FET
Implementation Method 2
This capacitor network, properly implemented in the module, channels the ringing energies from the capacitor associated with the sync transistor at the output switch node through the capacitor network into the ground node
Data Source
AI summary
A power supply module (400) comprising a metal leadframe with a pad (401) and a first metal clip (440) including a plate (440a), an extension (440b) and a ridge (440c); the plate and extension are spaced from the leadframe pad, and the ridge connected to an input supply. A synchronous Buck converter is in the space between the clip plate and the leadframe pad, the converter including a control FET die (410) soldered onto a sync FET die (420), the clip plate soldered to the control die having an input inductance (462), and the sync die soldered to the leadframe pad having an output capacitance. A capacitor (480a, 480b) integrated into the space between the clip extension and the leadframe pad, the clip extension soldered to the capacitor having a desired integrated inductance (463) operable to channel electrical energy from the switch node to ground.