Current Limit Test Circuit Using Switched Open-Path Measurement

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Solution Overview

Problem

Current methods for measuring the current limit of integrated circuits (ICs) are prone to inaccuracies due to increased operational heat and limited automated test equipment (ATE) capabilities, particularly when ramping currents, leading to measurement errors and reduced testing device reliability.

Innovation Solution

An integrated circuit design incorporating a signal path with a switching device and a comparator that enables accurate current limit measurement by disabling the switching device during voltage ramping and enabling it once the comparator transitions, allowing for a differential voltage measurement across an open circuit and subsequent determination of the current limit through a test current applied across a resistance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If current is ramped upward to measure IC current limit, then current limit measurement is obtained, but measurement accuracy deteriorates due to increased operational heat

Engineering Contradiction:

Improvecurrent limit measurement accuracyVSAvoidoperational heat

Core Design Contradiction:

Measurement precisionVSTemperature

Solution Approach 1:

The switching device is opened before applying test voltage to eliminate heat generation during the voltage ramp phase. The voltage is ramped up to the desired level while the switching device remains open, so no current flows and no heat is generated. This preliminary action of opening the switch before voltage application resolves the contradiction by preparing the test condition without the harmful thermal effect.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The testing process is segmented into distinct phases: voltage ramping phase (with switching device open) and current measurement phase (with switching device closed). By separating the voltage application from the current flow, the method allows accurate voltage ramping without heat generation, then closes the switch only when needed for current measurement, thus resolving the heat-accuracy contradiction.

Inventive Principle:

Principle #1Segmentation

2Temperature

If downward scaled current ramp is used to reduce heat, then heat generation is reduced, but measurement accuracy deteriorates due to gain scale inaccuracies

Engineering Contradiction:

Improveoperational heatVSAvoidcurrent limit measurement accuracy

Core Design Contradiction:

TemperatureVSMeasurement precision

Solution Approach 1:

The switching device acts as an intermediary that controls when current flows through the signal path. By using this intermediary component, the system can apply full test voltage without proportional current (when switch is open), eliminating heat. Then the switch closes to allow current flow only during the brief measurement window, achieving both low heat and high measurement accuracy without needing gain scaling.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Temperature

If testing speed is increased to reduce heat exposure time, then heat generation is reduced, but measurement accuracy deteriorates due to insufficient signal settling time

Engineering Contradiction:

Improveoperational heatVSAvoidsignal measurement accuracy

Core Design Contradiction:

TemperatureVSMeasurement precision

Solution Approach 1:

The testing method uses periodic action by repeatedly opening and closing the switching device. The switch is closed for brief periodic intervals during which current flows and measurements are taken, then opened to eliminate heat. This periodic switching allows the signal to settle during the closed interval while limiting total heat exposure through the open intervals, resolving the contradiction between speed and accuracy.

Inventive Principle:

Principle #19Periodic action

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 approach reduces measurement errors by minimizing heat generation and allows for more accurate determination of the current limit, enhancing IC specification reliability and reducing customer costs associated with inaccurate device specifications.

Implementation Method 1

a comparator having a first input coupled to the first node and a second input coupled to the second node, the comparator configured to receive a reference voltage and compare to the reference voltage a differential voltage between the first input and the second input

Methodology Applied

Scientific EffectVoltage comparison:

Implementation Method 2

a switching device coupled between a first node and a second node along the signal path; disable circuitry configured to open the switching device while a voltage is applied between the first node and the second node; enable circuitry configured to close the switching device while a device current is applied through the switching device

Methodology Applied

Scientific EffectElectrical switching: