Generating Negative Voltages—
Why You Need Level Shifting in
Buck-Boost Circuits
By Frederik Dostal, Field Applications Engineer, Analog Devices, Inc.
Introduction
The magnitude of the negative voltage generated by inverting
buck-boost circuits can be higher or lower than that of the
available positive voltage. For example, −8 V or even −14 V can be
generated from +12 V. When working with a switching regulator
IC with an inverting buck-boost circuit, communications pins
may be needed in the system design. If they are, it is essential
for designers to remember adequate level shifting so that
synchronization and enable signals can be utilized.
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What to Consider When Designing Level
Shift Circuits
The inverting buck-boost topology is one of the basic switching
regulator topologies, requiring just one inductor, two capacitors,
and two MOSFETs as switches. The switches can be driven with
any buck regulator or controller, so the availability of possible
switching regulator building blocks is large. Figure 1 shows the
inverting topology with all the necessary components.
Figure 1: An inverting buck-boost topology for generating a negative voltage with a step-down (buck) switching regulator.
(Source: Analog Devices)
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