Current Sense Circuit With Resistor-Based ESD Protection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Power transistors are susceptible to electrostatic discharge, which can damage the sense transistor used for accurate current sensing, particularly at the source node, compromising the accuracy of current measurement.
Innovation Solution
Incorporating a protective resistor between the source nodes of the power and sense transistors to share the electrostatic discharge charge, maintaining accurate current sensing while protecting the sense transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sense transistor is used to measure current through a power transistor, then current sensing accuracy is improved, but the sense transistor becomes more susceptible to electrostatic discharge damage
Solution Approach 1:
A protective resistor is introduced as an intermediary element between the sense transistor source and the power transistor source. This resistor acts as a mediator that limits the flow of electrostatic discharge current, protecting the sense transistor from damage while allowing normal operation. The resistor value is carefully selected to provide adequate protection without significantly affecting the current sensing accuracy.
2Measurement precision
If the sense transistor is made smaller to reduce parasitic effects, then measurement precision is improved, but the transistor becomes more vulnerable to electrostatic discharge
Solution Approach 1:
The protective resistor serves as a shield that intercepts and limits harmful electrostatic discharge currents before they can damage the small sense transistor. This intermediary element enables the use of smaller, more precise transistors by compensating for their increased vulnerability to electrostatic damage.
3Reliability
If a protective resistor is added to protect the sense transistor from electrostatic discharge, then reliability is improved, but circuit complexity increases
Solution Approach 1:
A simple, low-cost resistor is used as a disposable protective element that absorbs electrostatic discharge energy. This inexpensive component provides robust protection against electrostatic damage without requiring complex protection circuits or expensive specialized devices.
Solution Approach 2:
The protective resistor is inserted in series with the sense transistor source connection, adding only one simple element to the existing circuit. This intermediary component provides electrostatic discharge protection with minimal impact on the overall circuit architecture and operation.
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 protective resistor effectively shares electrostatic discharge charge between the power and sense transistors, ensuring accurate current sensing and protecting the sense transistor from damage.
Implementation Method 1
the small sense transistor may be more susceptible to damage from electrostatic discharge, particularly at the source node of the sense transistor. Electrostatic discharge can occur, for example, during manufacture when the circuit is being handled by a human, machinery, a testing probe, or other objects that may carry charge.
Implementation Method 2
the circuit includes the protective resistor placed between the source node of the sense transistor and the source node of the power transistor. Accordingly, when the circuit is exposed to electrostatic discharge at the source of the sense transistor, the large influx of charge that would have otherwise damaged the small sense transistor is instead shared between the sense transistor and the power transistor via the protective resistor.
Data Source
AI summary
A circuit that allows for accurate power transistor current sensing and electrostatic discharge protection. The circuit includes a power field-effect transistor and a sense field-effect transistor. The sense transistor current is proportional to (but much smaller than) the power transistor current. Thus, the power transistor current may be measured by measuring instead the sense transistor current. The gate nodes of the transistors are connected together, and the drain nodes of the transistors are connected together. However, the source nodes of the transistors are not directly connected to each other, and are instead connected together via a protective resistor. When the circuit is exposed to electrostatic discharge at the source of the sense transistor, the influx of charge that would have otherwise damaged the sense transistor is instead shared between both transistors via the protective resistor.