Author: Frederik dostaladi Field Application Engineer

Ć UK topology is very suitable for generating negative output voltage from positive supply voltage. Many systems require a negative supply voltage to read signals from some sensors. Therefore, it may be necessary to supply (for example) + 5V and – 5V, or even + 15V and – 15V, to the signal chain. Negative supply voltage is also used to safely switch some switching elements, such as silicon carbide (SIC).

Ć The UK topology is also known as the 2l invert topology because it requires two inductors in its power path. Figure 1 shows the Ć The circuit diagram of UK topology.

Figure 1. A method for generating a negative supply voltage Ć UK topology schematic diagram.

It is very important to ensure that there is a negative supply voltage feedback pin when selecting a suitable switching regulator IC. ADI has a large number of monolithic switching regulator ICs with integrated switches and Controller ICs with external switching transistors, which are suitable for such applications.

Most importantly, the two inductors required represent cost and space factors respectively. However, these two components also cause inductance in the power path of the input and output. This prevents fast switching currents at the input and output. Therefore, Ć UK topology is usually regarded as a specific low noise topology. Of course, like other switching regulators, Ć UK topology also provides switching current. In Figure 1, they are shown as thermal loops (blue). Thermal loop is a set of trajectories with fast di / dt transients. In order to minimize the interference caused by switching current and the parasitic capacitance, the space occupied by the circuit must be minimized.

Therefore, it is suitable for Ć In the optimized board layout of UK topology, freewheeling diode D, coupling capacitor C and switch S1 must be very close to each other. These circuits can be arranged compactly by using the corresponding IC pin arrangement, such as lt8330. Figure 2 shows the area where the power path of the switched current (hot loop) is located in the actual board layout.

The key circuit consists of external diode D, coupling capacitor C and internal connection between GND and SW pins in lt8330 switching regulator IC. The thermal circuit should be as short and compact as possible.

Figure 2. For Ć UK topology optimization board layout.

Figure 3 shows an example of a circuit containing the lt8330, which is shown in the Ć UK topology can be used as voltage regulator. An important feature is the FBX pin, which is a special FB pin that can handle negative supply voltage (according to the Ć UK topology requirements) and positive supply voltage. If the lt8330 is used in boost or SEPIC topology, it needs to have positive feedback pin polarity.

Figure 3. Using lt8330 Ć UK regulator circuit example.

The inductances at the input and output of the regulator will affect the conducted emission produced by the regulator. An extremely low noise solution can be achieved if an optimized board layout with a very compact thermal circuit is used. These characteristics make Ć UK regulators are ideal for generating low noise and negative supply voltage.

About the author

Frederik Dostal studied microelectronics at the University of Erlangen in Germany. He started work in 2001 and has been involved in power management business. He has held various application engineer positions and worked in Phoenix, Arizona for four years, responsible for switching mode power supply. He joined ADI in 2009 and worked as a power management field application engineer at ADI Munich.

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