Cascoded Power Switches for Cross-Conduction and Voltage Protection
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Solution Overview
Problem
Existing DC-DC converters face challenges in managing inductive voltage drops and preventing cross conductance between high-side and low-side power switches, which can lead to device damage due to excessive voltage ratings.
Innovation Solution
Implementing cascoded power switches with driver circuits that include voltage monitor circuits to control the gate voltages of high-side and low-side switches, using PMOS and NMOS transistors in series, and employing mid-rail biases to manage voltage transitions and prevent cross conductance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-side and low-side power switches are used in DC-DC converter, then voltage conversion function is achieved, but cross conductance between switches and excessive voltage may damage devices
Solution Approach 1:
The power switch is segmented into cascoded transistors (e.g., PMOS transistors P1-P4 in series combinations) with intermediate nodes, allowing voltage distribution and monitoring across multiple devices rather than a single switch, thereby protecting against excessive voltage while enabling conversion function
Solution Approach 2:
Voltage monitor circuits are introduced as intermediary components that detect intermediate node voltages and control switch operation, preventing cross conductance and excessive voltage conditions without requiring complex external control systems
2Reliability
If cascoded power switches with voltage monitor circuits are implemented, then cross conductance is prevented and switches are protected from excessive voltages, but device complexity increases
Solution Approach 1:
The voltage monitor circuits are merged with the power switch structure itself, using the same intermediate nodes and integrating control logic within the switch block, which reduces overall system complexity while maintaining protection functionality
Solution Approach 2:
The cascoded switch structure with voltage monitoring enables self-protection against excessive voltages and cross conductance through automatic detection and control, eliminating the need for external protection circuits and reducing overall system complexity
Data Source
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AI summary
A cascoded power switch includes a high-side (HS) switch coupled between an output node configured to provide an output voltage and a first voltage supply terminal configured to provide a first voltage supply, and a low-side (LS) switch coupled between the output node and a second voltage supply terminal configured to provide a second voltage supply. The LS switch includes a first transistor coupled between a middle node and the second voltage supply terminal, and a second transistor coupled between the middle node and the output node. The LS driver has a voltage monitoring circuit configured to receive a first control signal which, when negated, turns off the HS switch. The voltage monitoring circuit includes a logic circuit having a first input configured to receive the first control signal and a second input coupled to the middle node, and an output coupled to a control electrode of the first transistor.