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Test Op-Amp Power Rail Loading

Mike Donnelly
Designer19

Mike Donnelly

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10 years 5 months

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Member of the PartQuest Explore Development Team. Focused on modeling and simulation of analog, mixed-signal and multi-discipline systems covering a broad range of applications, including power electronics, controls and mechatronic systems.

Description

Design example from the Webinar: “Creating New Components, Part 1: Datasheet Model Builder”. View the archive presentation here: http://www.systemvision.com/webinarsThis example shows the value of including the output current of an op-amp model, in the rail current load it applies to the external supply circuit. In this example, the requirement is that the sensor signal amplifier circuit continues to function for 100 milliseconds after the external power is disconnected (e.g. an airbag sensor circuit). If the designers are trying to select capacitors of sufficient size to supply the op-amp power for that duration, then accounting for all the op-amp load current draw it essential.You can toggle the op-amp's "enable_supply_loading" to see the impact of this difference. With the "enable_supply_loading" unchecked, you can connect a static 5.5k Ohm "equivalent" op-amp load resistor to represent the "worst case" 1.8 mA quiescent current load of the op-amp, The output voltage of the op-amp will remain above the minimum 2 Vpeak-to-peak level for more than the required 100 milliseconds. But then if the "enable_supply_loading" is checked and the external resistor removed, the output voltage will decay long before the required operating time is reached.

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Test Op-Amp Power Rail Loading

Mike DonnellyDesigner19

Mike Donnelly

Member for

Mike Donnelly
Designer19