How to miniaturize your power supply

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Miniaturization has always been a pervasive theme in the electronics industry and is particularly important for power supplies. The quality of a power supply is often expressed in terms of power per volume. This article discusses some power supply design considerations that can help achieve miniaturization.

Minimize the number of external components

A power supply normally consists of at least a semiconductor and external passive components such as an inductor, capacitors and some resistors. Reduce the number of components to those indicated in Figure 1 is the first step towards reducing the size of the overall power supply.

If other functions, such as an adjustable output voltage or an adjustable soft start time, are required, this increases the number of passive components and thus the overall solution footprint. The circuit in Figure 1 is an example of a switching buck converter with a minimum number of passive components required.

Minimize the size of external components

For the smallest possible output capacitor and inductor sizes, the switching regulator IC should have the highest possible switching frequency. The voltage ripple of the output voltage behaves mostly linear with respect to the value and therefore the size of the external components. For example, if the switching frequency is doubled, the required inductance value is halved for the same output voltage ripple. This allows for smaller designs.

Figure 2 shows the space requirements for an LTC3307A switching regulator. Due to the high switching frequency of 3 MHz, a small inductor can be used.

Minimize the size of the switching regulator IC

Analog Devices’ LTC33xx platform consists of step-down switching voltage converters that convert with high switching frequencies of up to 5 MHz. For example, the LTC3315A has been optimized for space-constrained applications. This is a dual converter with two channels that can each supply 2A of output current in a 1.64×1.64mm wafer-level die-scale package (WLCSP) (Fig.3).

Another example is the MAX77324 single-channel buck switching regulator. It has a maximum output current of 1.5A and comes in a 1.22×0.85mm package. Figure 4 shows the footprint of the MAX77324 enclosure.

Size reduction thanks to the integrated inductor

Another way to reduce the size of the power supply circuit is to combine the inductor with the switching regulator IC. This combination is called a module. Integration helps reduce edge length by allowing the inductor to be placed on the semiconductor IC.

Another obstacle to miniaturization can also be overcome by using the inductor in the module as a heat conductor and heat sink. With the correct connection of the inductor to the silicon in the power module, the heat of the semiconductor can be dissipated extremely well. Especially for small switching regulator ICs with high output currents, heat dissipation becomes a bigger issue because silicon cannot be operated above the maximum allowable operating temperature.

There are many ways to reduce the size of a power supply using innovative techniques. This brief power management tip has covered a few of them. Miniaturization brings additional indirect benefits, such as lower costs due to smaller board footprint, the ability to build technical devices with higher functionality and therefore greater benefit, and even higher transportation costs. lower thanks to smaller and lighter electronic devices.

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Alan A. Seibert