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Buck-boost converter has 96 percent efficiency and 6µA quiescent current

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By Nick Flaherty

Maxim Integrated has developed a 1.5A buck-boost converter with higher efficiency and lower quiescent power for portable battery designs. A number of chip makers are pushing both efficiency and quiescent current in single chip DC-DC converter designs. 

The MAX77827 buck-boost converter allows 1.8V to 5.5V input and 2.3V to 5.3V output, while providing the system stability needed to minimize abrupt or unexpected shutdowns. It is aimed at low-power wide-area network (LPWAN) applications, asset tracking devices and many internet of things (IoT) applications with an 96 percent efficiency and 6µA quiescent current.

The growing lithium-ion battery market is largely driven by an increasing inclination towards smart electronic devices with expanding functionalities packed within. Primary cell batteries based on Lithium Thionyl Chloride (Li-SOCl2) chemistry or dual-cell Alkaline (AA or AAA) with operations as low as 1.8V is also gaining popularity in the long-life portable market segment. However, regardless of the types of batteries used, these devices will discharge through a wide range of voltages while sustaining a power rail between 2.8V to 3.8V, specifically for powering MCU, Wi-Fi, BLE and GPS features. The traditional buck or bypass boost plus low dropout (LDO) topologies are not ideal solutions for these sophisticated devices because they are not the most efficient at prolonging battery life. Additionally, a simple buck converter topology may cause earlier system shutdown when battery voltage is high to maintain the required power for the aforementioned applications, leaving underutilized battery capacity.

With the lowest quiescent current in the market, highest efficiency gains and small solution size, the MAX77827 buck-boost converter sets the standard for maximizing battery life. It is an ideal solution to support applications with low power requirements because, regardless of the battery voltage variations, it can automatically transition between buck and boost modes to provide a consistent output power supply.

Next: Buck-boost converter comparisons


Compared with using a bypass boost converter followed by an LDO, the MAX77827 improves efficiency by up to 12 percent. Compared with a buck converter, it allows continuous system operation with lower voltage from the battery to further boost the battery capacity. 

The buck-boost converter provides system stability to minimize abrupt or unexpected shutdown, including fast line transient response for a seamless mode transition between buck and boost modes to keep systems running steadily. During mode transition when VOUT is set to 3.3V with a 15µs rise/fall time, the ripple is less than 1 percent of the output voltage. Fast load transient response provides stable system voltage from transient loads pulling down the system voltage. In extreme harsh conditions of going from 0A to 1A load in 15µs, MAX77827 undershoot is controlled to 6 percent of the output voltage where the undershoot of the competitive solution is 12 percent with a longer recovery time.

For space-constrained designs, the 2.04mm x 1.64mm WLP package allows a buck-boost converter board footprint under 15mm². It uses a single external resistor to set the output voltage to provide additional savings to an external component and board space.

“High adoption of lithium ion batteries in smart consumer electronics is driving the increasing demand for this market, which is projected to reach $106,493 million by 2024,” said Rishab Sharma, analyst for P&S Intelligence. “Complimentary technologies that help prolong battery life and stability can only contribute to their continued growth.”

The MAX77827 is available at Maxim’s website for $0.84 (1000-up, FOB USA); also available from authorized distributors. The MAX77827EVKIT# evaluation kit is available for $50

bit.ly/MAX77827_Buck_Boost

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