Always-on buck converter, a key component of the USB 3.1 Type-C power management system
Maxim's MAX77596, offering low quiescent current and high efficiency, is recommended.

Recently, when a commercial for S Company's laptop showed a laptop being charged with a regular auxiliary battery at the end, many people asked questions.

'Can I charge my laptop with a spare battery?'

The reason why people could surprisingly pay so much attention to a feature that seemed ordinary is because of the 'USB Type-C' technology. In particular, the new USB 3.1 Type-C standard has the advantage of enabling data and power transfer between two devices using the same Type-C cable. USB 3.1 can transfer data at 10Gbps while delivering up to 3A of current with a standard cable and up to 5A with a reinforced cable. Many laptops today use less than 100W of power, so new models that adopt the Type-C connector can be charged via a USB port, which is a way to charge small devices.

However, there are more than one or two things to consider for engineers designing devices that support the USB 3.1 Type C standard. Because the USB 3.1 Type-C standard is complex, it must determine whether a device is a power source or a power sink before transferring power, and Type-C cables also require additional circuitry to determine exactly where power and data should travel.

It plays an important role in all stages of the power system and must consume minimal power.

A closer look at the USB 3.1 Type-C power management system reveals that the "always-on buck converter" is a key component in the essential handshake between source and sink devices. The always-on buck converter plays a crucial role at every stage, drawing power from the battery or Schottky diode of the USB source and then powering the port controller, which mediates the power exchange between the host system microprocessor (µP) and the power source.

The reason a buck converter must always be on is because the power source can change functions at any time during normal operation, requiring the sink device to be able to recalibrate. Minimizing power consumption is crucial. In this regard, Maxim Integrated's MAX77596, with its 98% duty cycle, is the optimal choice for battery-powered applications.

The MAX77596, a compact synchronous buck converter with integrated switches, is designed to deliver up to 300mA from a 3.5V to 24V input while consuming only 1.1µA of quiescent current at no load. This adjustable buck converter features a resistor-divider-programmable output voltage from 1V to 10V and reduces component count thanks to its on-chip power transistor switches. The MAX77596 provides both forced PWM and skip operating modes.

Maxim explained, “The USB 3.1 Type-C standard delivers more power to more devices with a single Type-C cable. The always-on buck converter (MAX77596), which supports USB Type-C applications, is differentiated by its best-in-class low quiescent current and high efficiency.”

Now, engineers may need to change the question people ask, "Can you charge your laptop with a spare battery?" to " Can you achieve both low power and efficiency with a single always-on buck converter?"