SIMO converter targets IoT with wide load range

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Toshiba claims its SIMO DC-DC converter, which has a load range of 1μW to 50mW, is efficient enough to extend battery life of IoT devices.

Toshiba Corp.'s on-chip Single-Inductor Multiple-Output (SIMO) DC-DC converter runs on coin-type lithium-ion batteries and is, according to the company, 100 times more efficient than a typical SIMO DC-DC converter. That, Toshiba hopes, will find the converter a place inside IoT devices because of the potential to extend battery life.

To supply multiple voltages, multiple external inductors are required in a conventional DC-DC converter, but a SIMO DC-DC converter needs only one external inductor. This advantage in reducing device cost and volume has stimulated widespread R&D of SIMO DC-DC converters.

IoT needs wide load range

Since an IoT device is mostly in standby mode (with <1mW power consumption) and in active mode (at tens of mW power), SIMO DC-DC converters must support a wide load range with high conversion efficiency. However, typical SIMO DC-DC converters were not designed for IoT applications, which require such support.

To address the issue, Toshiba has improved the SIMO DC-DC converter efficiency in the light load range. The comparator of the conventional control circuit is replaced with a control circuit that consists of only logic gates, reducing power consumption.

In addition, the switching frequency of switches that distribute current to output channels is reduced by a new operation mode. As a result, Toshiba’s new SIMO DC-DC converter achieves over 80% efficiency when the load power is above 5µW and about 65% when the load power is 1µW.

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Figure 1: With a wide load range, the SIMO DC-DC converter supports IoT devices more efficiently than typical SIMO DC-DC converters.

Toshiba has also improved efficiency in the tens of mW load range. Conventional analog control required a long wait time before channel switching to prevent interference between output channels of a SIMO DC-DC converter, degrading efficiency in this load range. The new SIMO DC-DC converter uses digital feedback control to minimise waiting time.

The architecture supports Toshiba’s SIMO DC-DC converter in achieving 65% to 86% efficiency with a load range from 1µW to 50mW.

Toshiba plans to use the SIMO DC-DC converter in low-power Bluetooth devices in the future.

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