Integrated DC-DC Converter Current Sensing Circuit
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Solution Overview
Problem
Existing current measurement circuits in switching regulator circuits are susceptible to noise pickup due to external sense resistors, which complicates PCB layouts and affects performance.
Innovation Solution
A DC-DC converter circuit with an internal sense resistor and a reference resistor, where the measurement current is proportional to the load current, independent of the actual sense resistor value, allowing for precise current sensing without external noise susceptibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an external sense resistor is used for current measurement, then the current sensing function is achieved, but the circuit becomes susceptible to noise pickup and PCB layout complexity increases
Solution Approach 1:
The patent combines the sense resistor and reference resistor into a single integrated circuit chip. The sense resistor is formed in the same semiconductor substrate as the reference resistor, eliminating the need for external sense resistors and their associated noise susceptibility and PCB layout complexity.
Solution Approach 2:
The patent introduces a reference resistor as an intermediary element that is matched to the sense resistor. By matching the temperature coefficients and forming both resistors from the same material on the same chip, the reference resistor serves as a stable reference that compensates for variations in the sense resistor, enabling accurate current measurement without external components.
2Measurement precision
If an external sense resistor is used, then current sensing is possible, but device complexity and PCB layout requirements increase
Solution Approach 1:
The patent merges the sense resistor and reference resistor into a single integrated circuit package. Both resistors are formed on the same semiconductor chip, eliminating the need for separate external sense resistors and reducing PCB layout complexity to minimal connection traces.
Solution Approach 2:
The integrated circuit performs multiple functions: it provides current sensing through the sense resistor, temperature compensation through the matched reference resistor, and signal conditioning through the operational amplifier, all within a single device that replaces multiple discrete components.
3Stability of the object's composition
If resistors are formed from the same material on the same chip, then temperature stability is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent creates local matching by forming both the sense resistor and reference resistor from the same material in close proximity on the same semiconductor chip. This local formation ensures they experience identical temperature conditions and have matched temperature coefficients, achieving temperature stability while using standard manufacturing processes.
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 provides accurate and noise-immune current measurement, eliminating the need for external sense resistors and improving the stability and accuracy of current sensing in switching regulator circuits.
Implementation Method 1
A1's non-inverting input, connected to pin ISENSE−, is connected to the junction between RIND and CIND. In this configuration the high gain of A1 drives the voltage at pin ISENSE+ to essentially equal the voltage at pin ISENSE−, so that the voltage across capacitor CIND equal to VIND will be placed across RSENSE.
Implementation Method 2
External inductor L 110, with an inductance of L having DC resistance DCR, forms part of the low pass filter network with CFILTER that turns an applied pulse width modulated input signal into a steady state voltage output
Implementation Method 3
The inductor current (IL) therefore causes a voltage drop across FET 157 equal to the product of RDSon and the inductor current, which is related to the resistance of sense resistor 170 multiplied by the current sensed (ISEN).
Data Source
AI summary
An integrated circuit is configured to be coupled to a current sensing element and a set resistor having a resistance Rset. The integrated circuit comprises a sense resistor having a resistance Rsense. The sense resistor is coupled to an input of the integrated circuit such that a first sensed current from the current sensing element flows through the sense resistor. The integrated circuit also comprises a reference resistor having a resistance Rreference which is a fixed multiple of Rsense; and circuitry configured to produce an output current such that the value of the output current is proportional to a value of Rset and a fixed ratio between Rsense and Rreference.