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METHOD FOR ADJUSTING OP-AMP IC OUTPUT CURRENT AFTER ASSEMBLY

IP.com Disclosure Number: IPCOM000005747D
Original Publication Date: 1988-Oct-01
Included in the Prior Art Database: 2001-Nov-01
Document File: 2 page(s) / 84K

Publishing Venue

Motorola

Related People

Jim Edwards: AUTHOR

Abstract

In applications using operational amplifiers it is sometimes desirable to be able to program the output drive capability of the device after it is assembled into a package, or perhaps even after insertion into an operating circuit. This need is of particular importance with devices using a PNP current source as the pull-up element, since with these the supply current is largely determined by the output drive current. The main reason such current consuming output stages are used is that they allow the output pin to rise almost to the positive supply rail and are able to provide this function for less current overall, than a resistive pull-up.

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MOTOROLA Technical Developments Volume a October 1988

METHOD FOR ADJUSTING OPAMP IC OUTPUT CURRENT AFTER ASSEMBLY

by Jim Edwards

   In applications using operational amplifiers it is sometimes desirable to be able to program the output drive capability of the device after it is assembled into a package, or perhaps even after insertion into an operating circuit. This need is of particular importance with devices using a PNP current source as the pull-up element, since with these the supply current is largely determined by the output drive current. The main reason such current consuming output stages are used is that they allow the output pin to rise almost to the positive supply rail and are able to provide this function for less current overall, than a resistive pull-up.

   Because the load applied to an op-amp output can vary, even from customer to customer in the same module, it is wasteful to always set up the pull-up current to the high level required to meet the worst case example. .other customers often want the lowest supply current possible and that is not cnsistent with the worst case design. It is of course possible to make multiple versions of an IC with different output capabilities, but this is difficult to control in manufacturing and leads to multiple inventories, which is an undesirable cost penalty (there may also be a cost penalty associated with varying lot sizes for the various IC versions).

   Figures 1 and 2 below show two possible ways to avoid this difficulty by programming the device output current as a packaged part before assembly into a module, or better still after module assembly and at the time when the module is selected to become a specific specification. Both these examples use "zener-zap" technology to increase the output current of an...