In a traditional switching-regulator topology, each switching regulator needs a separate inductor for each output. These inductors are larger and costly, making them a disadvantage for smaller form factors. Linear regulators are another option since they are fast, compact and low noise but they are lossy. There is another option of using a hybrid of multiple low-dropout regulators (LDOs) with DC-DC converters but this would result in a larger design than using LDOs alone.

The SIMO architecture provides the best solution for tiny devices that require longer battery life, by integrating functionality in smaller devices that would otherwise require multiple discrete components. By reducing the number of required inductors while still maintaining switching converter efficiencies, a SIMO architecture represents an even better and nearly ideal topology for smaller, ultra-low-power designs.

Figure 1. SIMO architecture block diagram.

Inductor Saturation Current

Inductor saturation current (I_SAT) is the current where the inductance drops by a certain percentage, and is determined by the inductor’s core size for a given core material and construction. By combining several inductors into one, there is a benefit to the total inductor sizing required. A SIMO provides benefits from:

• Improved cost savings and footprint
• Quantization of available component values
• Time multiplexing: If one system is off when another is on, they can "share" their required I_SAT
• Averaging: Even when there are not exclusive time slots, the current usage peaks often occur at different times. This results in a reduced I_SAT requirement

Power Dissipation

Maxim’s SIMO converters offer an optimal tradeoff between footprint and dissipation. They are architected to offer the benefits of a DC-DC converter with the footprint of a single DC-DC plus several integrated LDOs. Also, by reducing the inductor count, spacing between inductors is also removed and this also contributes to the reduction of total footprint.

Figure 2. The MAX77650 PMIC provides low heat dissipation and small footprint for space-constrained, battery-powered devices such as hearables and wearables.

SIMO in PMICs

Our new power management ICs (PMICs), the MAX77650 and MAX77651, were designed with micropower SIMO buck-boost DC-DC converters. An integrated 150mA LDO in the PMICs provides ripple rejection for noise-sensitive applications. In the MAX77650/MAX77651, the SIMO provides three independently programmable power rails from a single inductor for an innovative power management solution. The high integration of SIMO architecture helps significantly reduce the overall solution size compared to other discrete solutions.