cool chip lt1970 power op amp with current limit

Posted on Feb 5, 2014

This week I want to share a new favorite chip of mine, the LT1970 power op amp from Linear Technology. This nifty device runs from a 36 V supply and can source or sink 500 mA. That`s not too unusual, but how about programmable current limiting, outputs to indicate over-temperature and over-current, and more Think of it as a four-quadrant power s

cool chip lt1970 power op amp with current limit
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upply on a chip, or as the source part of a source measurement unit. The first nice feature of the chip is the programmable current limit. The chip has two inputs, one for sourced current and one for sunk current, that accept a voltage from 0 V to 5 V. It compares these voltages against the current measured across an external sense resistor and limits its output when the measured current exceeds 1/10 the voltage on the relevant control pin. Differential input pins, independent of the output pin, are provided for the sense resistor. Another great feature is that the output stage has its own power pins. One of the neater trick  circuits out there is to boost the current capability of an op amp by using the power supply pins to drive external transistors. An ordinary op amp without separate power pins can also be used this way, but the bias current of the external transistors will be proportional to the op amp`s quiescent current, which means one will probably need a low quiescent current model. By pinning out the output stage`s power pins, the LT1970 makes it easier. This circuit ends up running the output transistors in class AB. The bias current in the transistors is controlled, in part, by the quiescent current of the op amp. When the op amp tries to increase the voltage of its output, it will deliver more current to the output, pulling that current from its power supply. That, in turn, changes the voltage on the base of...

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