The Ćuk topology is suitable for use when a negative (-) output voltage is desired from a positive (+) input voltage.


Negative voltage is required to read useful signals from certain sensors in many systems.

For example, you may need to provide +5V and -5V or +15V and -15V to a signal chain.

Negative voltage is also used when trying to safely switch switching elements such as silicon carbide (SiC).

The Ćuk topology is also called a 2L inverting topology because it requires two inductors in the power path. Figure 1 shows the circuit diagram of the Ćuk topology.

For this topology, when selecting a switching regulator IC, you must choose one that provides a feedback pin for the negative voltage.

For this purpose, Analog Devices offers a variety of products ranging from monolithic switching regulator ICs with integrated switches to controller ICs that can be used with external switching transistors.

Above all, this topology requires two inductors, which adds significant cost and space.

However, these two components generate inductance on both the input and output sides of the power path.

This inductance prevents fast switching currents on both the input and output.

Therefore, the Ćuk topology is considered to be a topology with extremely low noise. Of course, like all other switching regulators, the Ćuk topology also switches current.




The hot loop marked in blue in Figure 1 corresponds to this part.

The term hot loop refers to a set of traces that transition di/dt rapidly.

To minimize the interference caused by the switching current, the parasitic inductance must be as small as possible, and to do this, the size of this hot loop must be as small as possible.

Therefore, the optimal board layout for the Ćuk converter is to place the freewheeling diode D, coupling capacitor C, and switch S1 as close to each other as possible.

The LT8330 pinout is designed to meet these exact requirements. Figure 2 shows the power path portion (hot loop) of the switched current in the board layout.

This loop consists of an external diode D, a coupling capacitor C, and an internal connection between the GND and SW pins within the LT8330 switching regulator IC.

Therefore, it was designed to be compact to be a hot loop.




Figure 3 illustrates a circuit using the LT8330 as a regulator suitable for the Ćuk topology.

An important feature of this regulator is the FBX pin.

This is a special type of FB pin that can handle both negative and positive voltages, which is required in the Ćuk topology.

Positive feedback pin polarity is required when using the LT8330 in a boost or SEPIC topology.




The inductance on both the input and output sides of the regulator affects the amount of conducted radiation.

By designing the hot loop compactly and implementing an optimized board layout, a solution with very low noise can be achieved.all.

In this respect, the Ćuk regulator is suitable for use in generating low-noise negative voltage.

※ Author: Frederik Dostal FAE / Analog Devices, Inc.

Frederik Dostal graduated in microelectronics from the University of Erlangen, Nuremberg, Germany. He started his career in 2001 in the Power Management business unit and held various application positions, including four years in charge of switch mode power supplies in Phoenix, Arizona. He joined Analog Devices in 2009 and is currently a Field Application Engineer (FAE) for Power Management at Analog Devices in Munich. (Contact: frederik.dostal@analog.com)