One Smart Design: Low IQ Boost Converter
April 11, 2017
| By: Christine Young
Blogger, Maxim Integrated
Whether you’re listening to tunes on your earbuds or tracking physical activity during a week-long bike trip, you don’t want to have to constantly charge your device. That’s one of the driving factors behind Maxim’s nanoPower circuits. Keeping quiescent current low in power management as well as system monitoring circuits helps extend battery life in the end device.
At just 300nA, Maxim’s recently launched MAX17222 nanoPower boost converter delivers ultra-low quiescent current, ideal for battery-powered wearables and other small, portable electronic devices. The engineers behind this family of products are Arjunsimha Chaturbhuj and Apsara Ravish-Suvarna, both based at the company’s San Jose headquarters. They had a challenging assignment for these boost converters: push the supply current down lower than what’s currently available while also integrating True Shutdown mode, which disconnects the output from the input with no forward or reverse current to extend shelf life for end products. Their aim was to deliver circuits that would support the long battery life and small form factor requirements of portable devices such as wearables and internet of things (IoT) sensors.
(L-R) Apsara Ravish-Suvarna, Joe Van, and Arjunsimha Chaturbhuj are the brains behind the MAX17222
Reducing Component Count
There were several key challenges that the team overcame to create the product, said Chaturbhuj, who has worked at Maxim for about seven years. For one, the team had to be able to program the output voltage with a single resistor. Typically, two external resistors are used for this purpose. Reducing the external resistor count down to one helps to lower the supply current and also reduces external component costs. “The MAX17222 has a unique ability to read an external resistor to program output voltage in 33 different combinations,” Chaturbhuj noted. The team was able to achieve this by carefully architecting, designing, and laying out the resistor reading circuit. As Ravish-Suvarna, a two-year Maxim employee, noted, the team was constantly pushing the limits of different architectures to uncover limitations and working to optimize every stage of the design, without giving up on accuracy. As a result, she noted, they were able to get the circuit working on the first pass.
Another challenge the team overcame was the ability to start up and operate with high source impedance batteries (such as coin cell or smaller). Starting with the predecessor part, the MAX1722, which already has an architecture suitable for low-power designs, the team made modifications so that its new counterpart could operate in continuous conduction mode and, thus, deliver higher output currents. Balancing and trading-off between when to seamlessly enter and exit low-power mode, ultra-low power mode, and high-power mode resulted in high efficiencies throughout the load current range.
Questioning Every Design Detail
“The design process was challenging, fun, and the good part was that we improved on efficiencies from the previous generation,” Chaturbhuj noted. “What I’m most proud of is, we have a compelling product that Maxim can greatly benefit from and that pushes the boundaries of physics.”
He continued, “This part required us to question every detail of the design. I wasn’t afraid to go to the drawing board for every circuit and every detail at any point in the design cycle, even if it had to be done just a few weeks before tapeout. We should inspire other engineers not only at Maxim but in the industry to think this way.”
Ready to check out the MAX17222 boost converter? Visit the MAX17222 webpage for a variety of resources available to help you with your evaluation, including an EE Sim model for simulating your application and an evaluation board for design prototyping.