DC-to-DC converter design boosts coin cell IoT

November 11, 2016 // By Nick Flaherty
Toshiba has developed a new on-chip Single-Inductor Multiple-Output (SIMO) DC-DC converter for IoT devices that use coin-type lithium-ion batteries.

The converter design achieves 65%-to-86% efficiency in the load range from 1 μW to 50 mW, more than 100 times wider than that of a conventional SIMO DC-DC converter, extending the battery life of IoT devices. Toshiba plans to use the SIMO DC-DC converter in low-power ICs for IoT devices, including Bluetooth low energy, in the future.

IoT devices that rely on small capacity coin-type lithium-ion batteries need to save power by operating at minimum supply voltages in each circuit. A SIMO DC-DC converter needs only one external inductor for the multiple voltage rails, reducing device cost and volume. As an IoT device spends most of its life in standby mode (where power consumption is below 1 mW) and a small part of it in active mode (where power consumption is in the tens of mW), a SIMO DC-DC converters must support a wide load range with high conversion efficiency. 

Toshiba has improved SIMO DC-DC converter efficiency in the light load range. The highly sensitive comparator in a conventional control circuit is replaced with a new control circuit that consists of only digital logic gates, reducing the power consumption. The switching frequency of switches that distribute current to output channels is reduced by a new operating mode to achieve over 80% efficiency when the load power is above 5 μW and about 65% when the load power is 1 μW.

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

The load range in which the conversion efficiency exceeds 60% is more than 100 times wider than that of conventional SIMO DC-DC converters, and the new SIMO DC-DC converter extends the battery life of IoT devices that are driven by coin-type lithium-ion batteries.