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ROHM’s Nano Energy™ Buck Converter Realizes 10-Year Battery Life for IoT Devices

To run for 10 years from a single coin cell has become like a holy grail for the tiny devices we rely on to keep life ticking. With literally billions of smart objects being deployed to keep smart cities, factories, buildings and infrastructures safe, secure and energy efficient, they really need to last a lifetime without needing their batteries replaced at regular intervals.

Having a converter that exhibits both high efficiency and low power consumption is vital for smart objects that spend long periods in power-saving or standby modes. ROHM engineers assert the BD70522GUL can enable devices to operate as much as 1.4 times longer in standby when compared with other converters.

Achieving this target demands miserly energy management throughout all aspects of the design. ROHM is contributing to the effort with its latest integrated buck converter, the BD70522GUL. A combination of advanced features and energy-saving technologies keep efficiency above 90% across the entire load range, from below 10µA to full load at 500mA. In addition, the extremely low quiescent current of 180nA minimizes the energy demand of the converter itself; according to ROHM, this is the lowest quiescent current in the market today.

Highly Integrated Features

Before looking at the technologies that have contributed towards this remarkably frugal performance, let’s acknowledge that the BD70522GUL is extremely small, measuring just 1.76mm x 1.56mm x 0.57mm high, and that it integrates many essential features saving overall circuit size. After all, minimizing the size and bulk of smart devices is almost equally important to saving battery energy.

The converter’s integrated features include a built-in power MOSFET, feedback-loop compensation, and voltage-divider resistors that let the user select one of nine pre-set output voltages from 1.2V to 3.3V by connecting two voltage-select pins (VSEL1/2) to various combinations of ground, Vin, or open. This not only saves the board space otherwise occupied by output voltage-divider resistors but also saves calculating the resistance values needed to get the desired output. The BD70522GUL also integrates safety-discharge circuitry at the output, which is controlled internally by Enable and UVLO signals. In addition, support for switching frequencies of up to 1MHz allows small, lightweight external passives.

Energy-Saving Design

ROHM also brought its proprietary Nano Energy™ technology to this converter, which has made a large contribution towards trimming the quiescent current to a mere 180nA. Nano Energy applies low-current analogue techniques in the converter control circuitry and optimized analogue circuit-layout knowhow, all combined with ROHM's vertically integrated production system. The 0.35µm BiCDMOS power process enables the control and switching circuitry to be brought together efficiently on the same silicon, ultimately realizing the ultra-low current of 180nA to power all the on-chip circuitry.

In addition to the low RDS(ON) and switching energy of the integrated MOSFET, several other design features contribute to achieving the outstanding efficiency of 90+% extended across the entire load range. ROHM’s Seamless Switching Mode Control (SSMC) function, for example, automatically switches the load mode depending on the load current. When VIN becomes close to VOUT, the BD70522GUL stops switching and enters 100% duty-cycle mode. Otherwise, the device utilizes Constant On-Time control to operate in CCM (Continuous Current Mode) for medium and high load conditions and DCM (Discontinuous Current Mode) for light-load conditions.

More evidence of energy-saving attention to detail includes the converter’s Ultra-Low-Power (ULP) mode, which disables both the main and Power-Good comparators that usually monitor Vout and relies on a single Ultra-Low-Power Comparator (ULP Comp) to detect a decrease in VOUT and resume normal operation.

Get Started with Eval Board

ROHM is making it easy for developers to explore the new buck converter’s battery-saving properties by introducing the BD70522GUL-EVK-101 evaluation board. It includes all the required circuitry, including input and output capacitors and a 2.2µH inductor, and is easy to set up and connect. Two jumpers are provided for setting the output voltage. A DC power source in the range of 2.5V to 5.5V is connected across the ground (GND1 or GND3) and VSYS test points on the board. The load is connected across the GND1/GND3 and VO pins.

The converter is then ready to power up by turning on the power supply and enabling the BD70522GUL using the SW1 jumper on-board. Test points are provided for monitoring input and output voltages, to help develop the application, and there is also a test point to probe the IC’s Power-good pin.

Usefully compact at only 50mm x 50mm, and with mounting holes in each corner to simplify assembly for proof-of-concept or prototyping, the board provides a fast route to longer battery life. And for design engineers and developers, that can only be… a very good thing.

Find out more in our YouTube video, below:

The BD70522GUL buck converter is available from RS Components in two packaging options: a pack of 5 (171-4310) or reel of 3,000 (171-3898). The BD70522GUL-EVK-101 evaluation board is available too, RS stock number (171-3899).

Find out more about the BD70522GUL at ROHM, or download the datasheet below.

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6 Nov 2018, 10:49