# Slew Rate Limits

I'm trying to calculate slew rate of OPAMP.

1. Applied square wave with 3V peak value to VIN+ of OPAMP.
2. Connected VIN- to VOUT as a feedback.
3. Graphic of VOUT voltage can be seen below.

1. Calculate Peak value of VOUT.
2. Find the time value of %90 (Time%90) and %10 (Time%10) of VOUT.
3. SR = (Vpeak*9/10-Vpeak*1/10)/(Time%90-Time%10)

I want to ask two basic question:

1. Is my slew rate calculation TRUE?
2. My OPAMP has the values of VDD +5V and VSS -5V. So should I apply square wave to OPAMP with 5V peak value? Or is it enough to apply square wave with 3V peak value.
• I don't think that's right... you'll be conflating GBW and SR. Just hit your opamp with a big (fast) step and measure how fast the output voltage rises... Volts/ uS. (They also list the value in the spec sheets... typically.) Commented Jan 10, 2017 at 16:16
• So how can I calculate Slew Rate? Commented Jan 10, 2017 at 16:18
• Do you have a 'scope? You can read the slew rate directly, as the rate of rise when you hit your opamp buffer with a large amplitude square wave. Commented Jan 10, 2017 at 16:21
• I'm using Pspice to simulate Commented Jan 10, 2017 at 16:22
• Well then plot the voltage vs. time... (just like a 'scope). I don't know much about opamp modeling in spice, but isn't the slew rate one of the input parameters Commented Jan 10, 2017 at 16:27