Kitronik Arcade for BBC micro: bit and MakeCode Arcade Many electronic designs, such as battery-powered systems, require powerful DC/DC converters to maintain a stable voltage output during input voltage fluctuations. Although four-switch step-down to step-up topologies are a common choice due to their flexibility and power density, there are significant design challenges when extending these systems to high current applications. The designer must carefully balance the architecture inside the step-down and step-up voltage regulators. Specifically, the integration of inductors and current detection devices will significantly affect the overall size, complexity and efficiency of the circuit.
This paper provides a brief overview of the challenges and trade-offs faced by power system designers. Subsequently, the solutions from the Analog Devices Buck and Boost Pressurizer product line are presented and how they address these challenges and optimize the design. Evaluation kits and software that designers can use to speed up prototyping and development are highlighted.
Integrated trade-offs in high-current step-down - step-up design
In a four-switch step-down to step-up converter, the power stage requires four MOSFETs, a power inductor and a current sensing device. How to allocate these components between module packages and printed circuit boards (PCBs) is a core architectural decision for designers.
External placement of inductors and detection resistors on PCBs gives the designer complete control over component selection. Inductor size, core material and saturation current can be accurately matched to the application. However, this flexibility is at a cost: external components occupy board space, complicate the layout, and require careful wiring to minimize noise in the current detection path.
Integrating inductors and detection resistors into the module package simplifies the design and layout, reducing the number of components and the footprint of the PCB. However, there are trade-offs: the inductor is limited by package size, which may limit the maximum output current and thermal performance.
In addition, the detection resistor can be replaced with a non-destructive current sensing scheme, thus completely eliminating the detection resistor. While this improves power efficiency, it results in more complex integrated circuit (IC) designs for step-down - boost modules.
How do the three module series cope with the step-down and step-up integration challenges
As part of its extensive µ Module product line,Analog Devices offers a wide range of DC/DC modules that enable designers to choose between these integration strategies. This paper focuses on the four-switch step-down - boost module (Figure 1): LTM4607, LTM4605 and LTM4; LTM8055, LTM8056 and LTM8054; And LTM4712. Each is for different areas within the input voltage and output current ranges.
Four-switch step-down - step-up µ Module graphic
Figure 1: The four-switch step-down - step-up µ modules are shown, which are constructed in different ways for different input voltages and output currents. Image Source: Analog Devices, modified by Kenton Williston)
DC/DC converter with external inductor and detection resistor
LTM4, LTM4605 and LTM4integrated controllers and MOSFETs in µ Module packages with power inductors and current sense resistors outside the circuit board (Figure 2). This structure allows designers to flexibly select inductor and inductor resistor values to meet specific application requirements.
Schematic Diagram of Analog Devices LTM4, LTM4605 and LTM4
Figure 2: Packaging (left) of LTM4607, LTM4605 and LTM4and corresponding power level schematic (right) with external inductors and induction resistors highlighted. Picture Source: Analog Devices)
LTM4, LTM4605 and LTM4pin compatible 15 mm x 15 mm x 2.82 mm LGA packages. The LTM4605 is designed for low voltage applications with an input voltage range of 4.5 V to 20 V and an output current of 12 A (reduced voltage mode). LTM4607 and LTM4extend the input range at 10 A (reduced voltage mode) to 36 V, with LTM4the widest output voltage range from 0.8 V to 34 V.
DC/DC converter with integrated inductor and detection resistor
LTM8055, LTM8056, and LTM8054 (Figure 3) integrate power inductors and current sense resistors into µ Module packages to simplify design and layout by reducing the number of external components on the PCB.
Schematic Diagram of Analog Devices LTM8055, LTM8054 and LTM8056
Figure 3 shows the module (left) of the LTM8055, LTM8054 and LTM8056 devices and highlights the schematic layout (right) of the integrated inductor and detection resistor. Picture Source: Analog Devices)
Of the three different series discussed in this paper, this series has the lowest output current: 5.4 A for LTM8054, 5.5 A for LTM8056, and 8.5 A for LTM8055 (all values in step-down mode). The LTM8056 has an input range of 5 V to 60 V, which is the widest of the devices discussed herein, and has a maximum output voltage of 48 V. The LTM8054 is the most compact, 15 mm x 11.25 mm footprint and 3.42 mm height for space-constrained designs. LTM8055 and LTM8056 are encapsulated in 15 mm x 15 mm x 4.92 mm.
DC/DC converter with integrated inductor and non-destructive current detection
LTM4712 (Figure 4) uses different current detection methods. Instead of using separate inspection resistors, it uses a proprietary NDI solution integrated in the module. This eliminates the power loss associated with the dedicated detection resistor.