PCBMASTER Takes You to Explore Six Practical Termination Strategies for Operational Amplifier Chips !

Author: Jack Wang

As the "commanding brain" in PCBA hardware, the chip itself plays the role of a commander. Therefore, operational amplifier chips are widely used in electronic circuits. When using an integrated dual operational amplifier chip to build a voltage follower, usually one operational amplifier is in operation while the other is idle. Properly terminating the idle operational amplifier is the key to stabilizing the performance of the circuit. Next, PCBMASTER will introduce to you six termination methods for operational amplifier chips and their characteristics.

I. Incorrect Termination Methods and Their Hazards

1. Leaving the Idle Terminals Floating (Bad Idea)

Some designers directly leave the unused terminals of the operational amplifier floating. This practice is incorrect. An open-loop operational amplifier is prone to saturate at the voltage of one of the power supply terminals. When the input terminals are floating, they are likely to capture noise, causing the output to fluctuate significantly between the two power supply terminals. It may also generate high-frequency signals, interfering with the normal operation of the circuit.

2. Partial Grounding (Never do)

Occasionally, some designers ground some pins of the operational amplifier, but this also has serious problems. Due to the existence of a potential gradient in the ground plane, a potential difference will be formed between the two input terminals of the operational amplifier, usually causing the operational amplifier to saturate at the voltage of one of the power supply terminals. Moreover, this saturated state is not stable. A slight voltage change at the pins may cause the operational amplifier to jump to the voltage of the other power supply terminal, bringing great uncertainty to the circuit.

3. Directly Connecting to the Power Supply (Do not do)

Although this method is slightly better than partial grounding, it is still not satisfactory. Designers just connect the operational amplifier to and keep it at the power supply voltage, which may lead to problems such as self-heating of the operational amplifier and increased power consumption. Long-term use may damage the operational amplifier chip and affect the reliability of the circuit.

4. Failure to Handle After Testing (Terrible)

Many engineers who design circuit boards for in-circuit testing do not properly handle the unused operational amplifiers after testing, leaving the output of the operational amplifier still at the power supply voltage. Although this is for testing purposes, this way of handling will leave potential hazards in the circuit, which may cause failures at any time.

II. Recommended Termination Methods and Their Advantages

1. Reasonable Potential Connection (Good Choice)

This is a basic and recommended circuit structure. Connect the non-inverting input terminal of the operational amplifier to an appropriate potential between the positive and negative power supplies. In a split power supply system, it can be directly grounded. When there is already a virtual ground in the system, the two resistors connected to the non-inverting input terminal can be omitted. In this way, the output of the operational amplifier is at the virtual ground (the ground potential in the split power supply system), which can prevent the abnormal operation of the operational amplifier and ensure the stability of the circuit.

2. Reserved Expansion Design (Fantastic)

When laying out the circuit board with a forward-looking design, reserve positions for resistors and jumpers for the unused operational amplifiers, which makes it convenient to configure them as inverting or non-inverting amplifiers as needed in the future. This improves the flexibility and scalability of the circuit and also leaves sufficient room for system upgrades and modifications.

If you encounter problems in the actual operation of terminating the operational amplifier chip, or if you want to further improve the circuit performance, PCBMASTER is willing to provide you with answers!