Imagine your life without a smartphone or tablet. It is almost impossible! From connecting with friends, checking emails, GPS, updating social media accounts, keeping up with news and much more, these devices have become indispensable from our daily lives. The ever-increasing data processing speeds require more function-packed application processors and therefore more power to deliver the performance. A higher battery capacity is required to meet the power budget and provide longer battery run-time and a better customer experience. The blog "Less is not more” shows the general trends for smartphone and tablet battery capacity. Figure 1 illustrates the battery capacity of different generations of smartphones.
Figure 1: Battery capacity of different generation smartphones
Higher-capacity batteries require higher charging current to maintain the standard charge time of about 3 hours at a 0.7C charging rate. Smartphone users also demand “power nap” (a quick and efficient charge for a short amount of time) for the phone to quickly charge in the car, airport, etc. The fast charging is not just limited to smartphones but can be applied to other personal accessories including portable speakers and wearables, for example. This same trend applies to industrial applications. Think of the point-of-sale or logistics tablets being on the road 24/7 and never given enough time to fully charge. Throughout all these examples is one common theme: batteries must be charged fast and efficiently.
In order to deliver higher charging power without increasing the cost of the USB connector, increasing the input voltage is the most desirable option. For example, customers who design with the bq24192 can charge their system with traditional USB charging, but can also set the input voltage up to 17V to provide more power to the device.
The high-voltage input in a charging system presents a paradigm shift, challenging conventional battery-charger designs. For example, the increased input voltage changes the loss distribution of a power converter in a charger. The conduction loss of the low-side switching FET is more significant due to the loss proportional to I2.
The newly launched bq25890, bq25892 and bq25895 MaxCharge TM family with 5A charge current takes a fresh look at charging from the high-input voltage perspective. The bq25892 family completely redesigns the power stage to minimize power loss for the best efficiency (91% at a 3A charge current) and thermal performance with high-voltage charging. The new design allows for faster, cooler, safer charging. The product family also provides features to facilitate high charging currents. One of these features is resistance compensation (IRComp). High charging current will induce a voltage drop on the charging path parasitic resistance and internal battery impedance. The battery cell’s 1000mAh normalized impedance is increased around 50% from the median 200mohm due to the high energy density in the past two years. Higher impedance will result in a longer charging time because the charging enters constant voltage mode prematurely. The IRComp increases the charger terminal voltage above the battery regulation voltage by the I x R drop so that the charger can stay in constant current mode long enough for fast charging.
Smartphone and tablet mobility requires fast charging for large-capacity batteries. High-input voltage delivers high-input power to a charger without increasing the input current. TI’s new MaxChargeTM technology combines years of TI charging expertise to push the boundaries of efficiency and thermal performance for faster and cooler charging.
Watch a video on How to achieve fast charging with high efficiency?
View the TI Designs reference design: 1S 5A Fast Charger with MaxCharge™ Technology for High Input Voltage and Adjustable USB OTG Boost
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