“Industry’s Smallest” Buck-Boost IC Could Shake Up USB PD Charging Systems

June 30, 2020 by Jake Hertz

This buck-boost converter comes at a time when universal battery charging is becoming a realistic possibility.

With the advent of USB-C, engineers and consumers alike have become enamored with the concept of universal battery charging. In general, consumers are burdened with needing multiple different types of adapters to charge their different devices.

The desire to design a universal charging solution, which can charge a battery from nearly any input source, has made the buck-boost converter a favorite for engineers. 


Universal Charging Systems and DC-DC Converters

In designing universal charging systems, engineers value buck-boost converters because they offer the ability to effectively charge a battery regardless of whether the input voltage is higher or lower than the battery voltage. Design engineers, however, want to add more functionality than just one-way charging and for this, other components are necessary. 

In order to support the USB on-the-go (OTG) specification, charging systems generally employ a DC-DC converter to power external devices when the adapter is disconnected. 


Graphic depicting different types of chargers needed for different battery-operated devices

Graphic depicting different types of chargers needed for different battery-operated devices. Image used courtesy of Texas Instruments


This is generally implemented with power inefficiency in mind to keep this DC-DC converter on, causing significant amounts of quiescent power dissipation. This tradeoff is one a design engineer must face when looking to implement fast role swapping in a power solution.


Power and Size are Key in Charging Solutions

Arguably the most important design consideration when creating a charging solution is power efficiency. For a charging system to be useful, it must be power efficient; this means that there must be minimal power loss between input and output. 

Area is an important design consideration that is closely tied to power. Today, consumers are demanding products such as smart speakers to scale down in size. Unfortunately, it often isn’t feasible to scale down systems that are power inefficient. 


Block diagram of an example of a USB PD charging solution

Block diagram of an example of a USB PD charging solution. Image used courtesy of Texas Instruments


For example, let’s say a system dissipates a lot of power in the form of heat given a certain area. Now, if we were to scale that system down to half the area while keeping the power constant, the heat per area would be twice as much. In this way, high power consumption per area can lead to unreliable systems and, in extreme cases, system failures.

This can be a notable hurdle for designers to overcome when scaling down charging systems.


TI’s New Buck-Boost Battery Charger ICs

Texas Instruments had many of these design pain points in mind when they created their BQ25790 and BQ25792 buck-boost battery charger ICs. 


Simplified schematic of the BQ25792

Simplified schematic of the BQ25792. Image used courtesy of Texas Instruments


These new ICs are said to simplify the system-level design thanks to their high level of feature integration. Notably, the ICs allow for bidirectional operation with a novel backup mode, which allows for the chip to support OTG mode and fast role swapping across the full USB PD voltage range, from 2.8 V to 22 V. This feature effectively eliminates the need for the aforementioned DC-DC converter. 


USB Type-C FRS realized by single buck-boost charger.

How USB Type-C FRS could be realized by a single buck-boost charger. Image used courtesy of Texas Instruments


Along with this, the IC notably boasts 97% power efficiency at 30 W. This power efficiency allowed TI to scale the chip down as “the industry’s smallest integrated, high-efficiency chargers.” Texas Instruments claims that the chargers deliver 155 mW/mm of power, making it have a power density up to two times more than competing devices. 


Aimed at USB PD and USB-C

For design engineers looking to create more universal charging systems while also scaling down their designs, this IC looks to be very useful. These chargers, aimed at USB PD applications, allow for a wide array of functionality, which could mean significantly simpler system designs. Offering simpler designs on the system level along with higher power density and smaller size makes for an attractive chip.

All in all, this chip could change the way engineers design their USB-C power systems.