Hi Alex,
Is the input current spec for OPA455 still valid in overdrive (saturation) mode? What is the maximum input current in saturation mode?
Could you be more specific about the inquiry? As Kai pointed out, we'd like to know the application and scenarios when if a saturation state is occurred.
The linear mode operation is shown below. The OPA455 is able to source/sink ±45mA max. at room temperature. We have another part in that is able to handle OPA462 higher voltage, with the same level of output current for HV application. OPA455 is implemented with overcurrent protection, so the IC will protect itself when maximum output exceeds ±45mA, is a function of temperature.
Regarding to the max (absolute), input current, it is limited to up to ±10mA per input pin. For a typical application, it is recommended that input current should be limited to ±1 to 2 mA.
A typical positive and negative overload recovery timings are provided in the datasheet, see the captured image. Please let us know what you are trying to do, and we may be able to simulate the conditions.
Best,
Raymond
TINA simulation for OPA455 (see attached schematics) indicates Op Amp input current of about 100 microamps, when Vin=40V and Vout=approx -75V.
So, here is the question: Is the model valid for saturation mode? Does it mean that OPA455 input current spec is not valid for saturation mode, when output voltage reaches supply rail?
Hi Alex,
Is the model valid for saturation mode? Does it mean that OPA455 input current spec is not valid for saturation mode, when output voltage reaches supply rail?
I duplicated your schematic and here is what it has.
Gain = -2 V/V, Vcc = 75Vdc and Vee = -75Vdc, Vin =40Vdc, and Vout should be equal to -80 Vdc, but the it exceeds the Vee supply rail, hence it is operating in non-linear mode (or saturation).
Since the op amp configuration is operating in non-linear mode, Vos will not follow GND node. As you can see VF1 = 1.4Vdc.
Iin = (Vin - VF1)/RI = (40-1.4)/10k = 3.86mA as simulated.
As far as the simulation goes, the Iin figure is valid. If you are asking if the identical OPA455 configuration is measured in a lab, will the actual input current follow the simulated circuit in this case? My guess is that it is unlikely. In other words, VF1 may not measure at 1.4Vdc exactly, but it should be pretty close (VF1 will not measure at 0V or GND), which it indicates that the op amp configuration is operating in non-linear mode.
The non-linear operating mode is not simulated, but the math calculation is still correct.
BTW, the Iin current should be kept at approx. 1-2mA range under the worst case operating conditions, see the absolute max. ratings in the previous reply.
If you have additional questions, please let me know.
Best,
Raymond
