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OPA541: Current slew rate specification of op-amps?

Mustafa Turhan
Prodigy 30 points
Part Number: OPA541

Hello,

I know that slew rate specifieshow fast the output voltage of an op-amp can change. But is there a measure that specifies how fast the output current of op-amps can change?

I need this information because I need to drive a capacitive load with a triangular voltage waveform. That means the the current waveform will be a square wave that swings from +Iout to -Iout. 

I did a simulation with OPA541 and saw that it can it can go from +180mA to -180mA in 2us. But it's an expensive IC so I want to use a cheaper op-amp. 

Here are the circuit schematic and simulation results:

  • 0
    TI__Guru 63050 points

    Mustafa,

    The timing response of the op amp output for any large input signal will be controlled by the slew rate UNLESS the capacitive load is large enough for the short-circuit output current to be a limiting factor.  In other words, the only time output will be slower than specified slew rate if the current demand will exceed op amp maximum output current capability (Isc).  Since: Ic = C*dV/dt, assuming OPA541 max output current of 8A, the op amp output will be slower than slew rate for: CL > Ic/(dV/dt) or CL > 8A/(10V/us) or CL> 800nF - see simulation below.

    Case 1: with CL of 470nF slew rate controls the output response.

    Case 2: with CL of 5uF, Isc 8A limit controls the output response (see Isc clipping below).