Compensation solutions for stabilising TS507 Op-amp

Article By : STMicroelectronics

Three compensation methods are applied to TS507 for identifying the best solution for op-amp stability.

Capacitive loads have a big impact on the stability of operational amplifier-based applications. Several compensation methods exist to stabilise a standard op-amp.

The general theory of each compensation method is explained, and based on this, specific data is provided for the TS507. The TS507 is a high precision rail-to-rail amplifier, with very low input offset voltage and a 1.9MHz gain bandwidth product, which is available in SOT23-5 and SO-8 packages.

The in-the-loop method is the most complex solution to understand, but a pick-up table is provided in order to choose the most appropriate components for your application. The main drawback of this compensation method is a limited output swing.

The out-of-the-loop compensation method is easy to implement because it requires only one extra component. The way it works is also easy to understand. However, its main limitation is an inaccuracy on the output voltage because the load is part of a divider bridge. An abacus is provided to choose the component you need for your application.

Finally, the snubber method is easy to understand and use. It does not have the drawbacks of the first two solutions. But because the loop gain cannot be considered as a pure third-order system (because of the open loop gain of the amplifier and the variations of the output impedance which is not purely resistive and constant over frequency), it does not lead to great improvements, and it is limited to load capacitors lower than 1nF in the case of the TS507. An abacus is also provided for this compensation method. Another drawback of this solution is that it potentially limits the frequency range of the application for large output signals due to a strong current flowing through the compensation elements. This compensation method is not really useful for the TS507.

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