Understanding Op-Amp Output Swing Limitations in Linear Applications

Explore the limitations of op-amp output swing in linear applications, focusing on the non-linear behavior when driven into saturation. Learn how open-loop voltage gain affects output swing and the implications of operating closer to the rails. Check datasheet specifications for op-amp constraints and how to calculate closed-loop gain effectively.

• Op-Amp
• Output Swing
• Linear Applications
• Voltage Gain
• Datasheet

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1. Op Amp Aol vs Vout Swing Tim Green & Art Kay 4/29/2014 Precision Analog Linear Applications 1

2. Datasheet Specifications OPA180 Specs for Discussion Output Voltage Output Swing from Rail Aol Open Loop Voltage Gain

3. Output Swing This is a NON-LINEAR test. The output is driven hard into output stage saturation.

4. Aol is NOT guaranteed closer than 500mV to either rail V+ = +18V V- = -18V Point A: Vout = (V+) - 0.5V Vos = 35uV Aol = 114dB A Point B: Vout = (V+) - 0.25V Vos = 6000uV Aol = 69.42dB Aol = x2958 B Point B Closed Loop Gain: Acl=Aol/(1+Aol ) Acl= 2958 / (1+2958*0.0065) Acl=146 Acl should be x154 !! Gets WORSE Closer to the rail the output swings! Note: Beyond point B is Test Equipment Range Limitation

5. Datasheet Specifications Check Op Amp Datasheet for Op Amp used in application circuit as ALL Op Amps have this limitation! Output Voltage Output Swing from Rail Output Saturation Specification Aol Open Loop Voltage Gain Measured in Linear Operating Range Note Vout Swing where Aol is Tested