Opamp Slew rate

Thread Starter

Sergen Erbay

Joined Dec 19, 2019
23
I found the circuit's slew rate as 14.7V / us.Slew rate value of the integrated I will use is 700V / us.(OPA657).Is it a problem if the Op Amp slew rate is higher than the slew rate in the circuit?
 

atferrari

Joined Jan 6, 2004
3,917
You do the equivalent with your car all the time; driving at 55 miles/hour when the car is able to do the double. Unless the cost is a concern.
 

OBW0549

Joined Mar 2, 2015
3,300
I found the circuit's slew rate as 14.7V / us.Slew rate value of the integrated I will use is 700V / us.(OPA657).Is it a problem if the Op Amp slew rate is higher than the slew rate in the circuit?
Not at all. It's a problem if the op amp's maximum available slew rate is lower than the slew rate your circuit needs, because that situation will cause distortion and/or clipping of the op amp's output signal.
 

dl324

Joined Mar 30, 2015
10,488
I found the circuit's slew rate as 14.7V / us.Slew rate value of the integrated I will use is 700V / us.(OPA657).Is it a problem if the Op Amp slew rate is higher than the slew rate in the circuit?
It isn't a problem, but it'll likely raise some eyebrows if someone analyzes your circuit.

I had an instructor who designed a circuit to be used in a satellite. He said used a 1W resistor when something smaller would have been sufficient because that was all he had available. If he had done that for every resistor, he might have impacted the fuel budget.
 

OBW0549

Joined Mar 2, 2015
3,300
It isn't a problem, but it'll likely raise some eyebrows if someone analyzes your circuit.
That's a good point. With its GBW product of 1.6 GHz and maximum slew rate of 700 V/μs, the OPA657 is much, MUCH faster than appears to be needed here. There's nothing wrong with that per se, but extreme wideband op amps can be very difficult to work with due to their ability to oscillate at VHF (or even UHF) frequencies if given the slightest excuse-- such as poor PCB layout, improper supply decoupling, unwanted crosstalk between signals, etc.

It's quite possible that a better choice would be a somewhat slower op amp which still has adequate slew rate and GBW. One example that might function adequately would be an LT1022 (23 V/μs and 8.5 MHz).

Could be worth looking at...
 

dl324

Joined Mar 30, 2015
10,488
To get a high slew rate, you have to give up something. Stability (i.e. lack of adequate compensation, supply decoupling,) and/or higher first stage current.
 
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