A high-accuracy operational amplifier can be used to configure a shunt resistor current sensor, a type of current sensor. Using high-accuracy operational amplifiers, especially ABLIC's zero-drift amplifiers, enables high-accuracy current sensors over the entire temperature and operating voltage range. However, have you experienced design issues such as operational amplifier oscillations, failure to achieve the design goal of detection accuracy or inability to reduce the impact of external noise in such a configuration?

This article describes an easy-to-follow example of designing low-side or high-side shunt resistor current sensors using a high-accuracy operational amplifier.

1. Current Sensor Types and Characteristics and Why Shunt Resistor Current Sensors Are Used

Current sensor types and characteristics

A current sensor is used to measure current flowing through a circuit.

Current sensors come in many types (shunt resistor, magnetic, etc.) As shown in the figure below, the type of sensor required depends on the current region it is to be used for.
Understanding different sensor types and using the right current sensor for the application are therefore essential.

Why use a shunt resistor current sensor?

The low-cost and high-accuracy current detection of a shunt resistor current sensor make it the most commonly used of the three current sensors described above. It is therefore widely used for applications such as battery current monitoring in automobiles and industrial equipment where high-accurate detection down to several tens of amperes or less is required, and for current control applications of solenoid valves operating hydraulic actuators.

 

2. What Type of Operational Amplifier (Signal Amplifier Circuit) Does a Shunt Resistor Current Sensor Require?

A shunt resistor current sensor consists of a shunt resistor and an amplifier (signal amplification circuit) for amplifying the voltage drop that occurs in the sensor.

Since as little as a few tens of amperes flowing through the shunt resistor is enough to cause power loss and heat generation issues, a shunt resistor with a low shunt resistance is used. As the voltage drop that occurs in the shunt resistor is minute, this requires an amplifier that can accurately amplify the minute input signals. A high-accuracy operational amplifier is used in the above amplifier.

Using a 1mΩ shunt resistor to detect 10A current with an accuracy of ±1%

±1%×10mV=±100μV
⇒ a signal amplifier with a ±100μV accuracy is required

 

3. Types of High-accuracy Operational Amplifiers and Advantages of a Zero-drift Amplifier

The input offset voltage is amplified with the input signal. For this reason, high-accuracy operational amplifiers with low input offset voltage and low temperature drift are widely used for current sensors and other applications that require high-accuracy amplification of minute signals.

Types of high-accuracy operational amplifiers

Depending on how the input offset voltage is corrected, high-accuracy operational amplifiers are of two kinds.

1. A regular high-accuracy operational amplifier without zero drift

This is an operational amplifier that does not automatically correct input offset voltage. Each operational amplifier is trimmed prior to shipment from the factory to minimize input offset voltage.

2. A zero drift amplifier

This type of operational amplifier automatically corrects input offset voltage. This operational amplifier integrates a circuit that automatically minimizes the input offset voltage during operation.

Advantages of a zero-drift amplifier

Differences in how the input offset voltage is corrected are reflected in output voltage characteristics. A zero-drift amplifier automatically corrects the input offset voltage and will at all times minimize input offset voltage without being impacted by ambient temperature or operational amplifier common-mode input voltage fluctuations.

ABLIC provides a full lineup of general and automotive use zero-drift operational amplifier products.

 

4. Solving Your Design Issues!

Introducing a design example of a shunt resistor current sensor configured using a zero-drift amplifier

The following describes a detailed design example of a shunt resistor current sensor configured using the S-19630A zero-drift amplifier.

The S-19630A is a zero-drift operational amplifier with a wide operating range (4.0 to 36V), a low input offset voltage of ±50μV max., and a low input offset voltage drift of ±25nV/°C.

A current sensor design using the S-19630A can do the following.

• Thanks to the low input offset voltage and low input offset voltage drift characteristics, it can be used to design a very high-accuracy current sensor whose current detection results are not impacted by temperature or power supply voltage fluctuations.
• Its wide operating range enables direct connection to a 5V, 12V or 24V system.
• Input Rail-to-Rail enables low-side and high-side current detection.

1. Design example of low-side current detection

2. Design example of high-side current detection

 

5. ABLIC's Development Support Service Dovetails with Customer Design Efforts

ABLIC's operational amplifier products are provided with a variety of services to help customers overcome problems or issues in each step of circuit development. Our products comply with all major automotive standards.

Support services for assisting in proposing circuits and setting constants

ABLIC offers consultation in circuit design. To reduce the number of prototypes, development time and development costs, and to optimize application cost performance, we propose the optimum combination of peripheral parts and our ICs.

Circuit simulation service

The operational amplifier started oscillating in the device evaluation after circuit design! Have you experienced such a problem? ABLIC performs a circuit simulation service to check that an operational amplifier will work without oscillating.

Service for providing PSpice models

ABLIC's zero-drift amplifier products are provided with PSpice models to reduce the number of prototypes the customer has to develop. You can download models from the pages listed below. We also offer a consultation service to help customers analyze simulation results using a PSpice model. If you are interested, feel free to call our sales office anytime.

Evaluation board service

ABLIC provides evaluation boards to help the customer in the evaluation of a device. And not just evaluation boards, but boards mounted with operational amplifier ICs and other peripheral parts. If you are interested, feel free to call our sales office anytime.