Introduction

The most common way to measure current is to sense the voltage drop across a shunt or current-sense resistor. This method requires two key components:

• A shunt or current-sense resistor

• A current-sense amplifier

To achieve high measurement accuracy with the components above, it is important to complete the following tasks:

• Carefully examine their parameters

• Create proper layout connections between them

The figure below shows a typical schematic for current sensing, with connections for both high-side current sensing and the critical design areas shaded.

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High-side Current Sensing with Shaded Areas of Importance

Applications

Battery Management Systems (BMS)

The main tasks of battery management systems are:

• Overcurrent protection

• Overvoltage protection during charging

• Charging/discharging current limiting

Proper battery management systems require continuous monitoring of current flow. The status of the battery is essential in automotive (and other) industries where rechargeable batteries are used.

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Current Sense Resistors in Battery Management Systems

DC/DC Converters

The efficiency needed in switching power supplies used in current-mode DC/DC converters is higher than traditional linear power supplies. High stability and power efficiency is extremely important to ensuring the safety of the sensitive circuits and to helping to extend valuable battery life.

The low TCR and low thermal EMF of current sense resistors minimizes or even eliminates the negative impact of self-heating of the devices and effects of various ambient temperatures.

Digital Motor Control

Digital control offers benefits such as faster loop responses allowing for integrated overcurrent protection as well as narrower dead times. This enables smoother output voltages that, in turn, contribute to improved torque control.

Current sense resistors are ideal solutions for motor controls due to their low resistance value of 0mΩ-2mΩ depending on the maximum power. Their low TCR helps designers to minimize the drift of the resistance with temperature. An important consideration in selecting a current sense resistor is that motor drivers will experience short circuits from time to time and the current sense resistor must be able to handle short overloads without being damaged.