Isolated Load Switch Driver IC With Current-Limited Single-Pin Input
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Solution Overview
Problem
Current load switch drivers for low voltage digital outputs face challenges in interfacing with high voltage loads due to high current requirements and electromagnetic interference, and existing solutions like relays and solid state relays often require separate power connections and have moving parts or optical isolation limitations.
Innovation Solution
The development of an isolated load switch driver IC that uses a current limiter circuit to charge a buffer capacitor, allowing controlled current flow and enabling a DC-DC converter for galvanic isolation without external power connections, using a single pin for both signal and power input, and integrating components like a buffer capacitor and output transistor to reduce complexity and pin count.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a relay is used to drive an isolated load, then galvanic isolation is achieved, but the current required to energize the relay coil exceeds what most digital outputs can supply and separate power connections are needed
Solution Approach 1:
The patent combines the signal input and power supply functions into a single pin. The buffer capacitor charges from the digital output pin, and the DC-DC converter extracts power from this charged capacitor, eliminating the need for separate power connections while maintaining galvanic isolation through the isolated DC-DC converter.
Solution Approach 2:
The circuit uses the digital output signal itself to charge the buffer capacitor, which then serves as the power source for the isolated DC-DC converter. The system is self-sufficient, drawing all necessary power from the signal pin without requiring external power connections.
2Reliability
If an opto-coupler is used for load switch driver, then optical isolation is achieved, but the solution requires separate power connections and has limited current control capability
Solution Approach 1:
The patent merges the signal input and power supply functions into a single pin, eliminating the need for separate power connections. The isolated DC-DC converter enables the circuit to draw all necessary power from the charged buffer capacitor, simplifying the connection requirements compared to opto-couplers.
3Reliability
If a transistor or relay driver is added to interface the relay coil with the digital output, then the relay can be energized, but the device complexity increases and separate power connections are still required
Solution Approach 1:
The patent combines multiple functions into a single integrated circuit that includes the buffer capacitor, current limiter circuit, and isolated DC-DC converter. This integration eliminates the need for external transistors or relay drivers while maintaining the ability to drive high-voltage loads.
Solution Approach 2:
The isolated load switch driver circuit draws all necessary power from the charged buffer capacitor through the DC-DC converter, making the circuit self-sufficient and eliminating the need for external power connections or additional driver components.
4Speed
If the buffer capacitor is charged directly without current limiting, then charging speed is fast, but the digital output pin may be overloaded
Solution Approach 1:
The current limiter circuit is designed to allow fast charging initially, then automatically activates when the buffer capacitor voltage reaches a threshold level. This preliminary fast charging followed by current limiting protects the digital output pin while minimizing charging time.
Solution Approach 2:
The current limiter circuit monitors the buffer capacitor voltage and automatically adjusts the charging current based on the voltage level. When the voltage reaches the threshold, the current limiting activates, creating a feedback mechanism that protects the digital output pin from overload.
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 solution provides efficient, galvanically isolated switching without moving parts or optical circuitry, reducing power consumption and pin count, and enabling the use of high-voltage load switching with lower current draw, facilitating integration into existing PCB designs.
Implementation Method 1
an impedance circuit that receives a digital input voltage signal from a signal source, and selectively allows a current signal to flow from the signal source to charge a buffer capacitor
Implementation Method 2
an output circuit provides an output isolated from the digital input voltage signal to switch the load
Data Source
AI summary
Disclosed examples include isolated load switch driver circuits to drive a load, including an impedance circuit that receives a digital input voltage signal from a signal source, and selectively allows a current signal to flow from the signal source to charge a buffer capacitor. An impedance control circuit controls the impedance circuit to limit the current signal in response to the buffer capacitor reaching a first threshold voltage, and an output circuit provides an output isolated from the digital input voltage signal to switch the load. A signaling circuit selectively enables the output circuit to draw power from the buffer capacitor in response to the voltage of the buffer capacitor reaching the first threshold voltage.