Discover why lithium-ion (Li-ion) is the dominant choice for small form factor markets and explore how onsemi has the industry-leading technology for Li-ion chargers in extremely small footprints for migration to smaller charging form factors.
Like the smartphone evolution of the last decade, other growing markets demand shrinking form factors coupled with added features and portability. The segmenting drone market is exhibiting growth in mini and micro drones. There is significant growth in the hearable, or earbud market, equipped with voice recognition, proximity sensors, noise cancellation and high fidelity. Small Bluetooth speakers now fit in the palm of your hand, and wearables—in the form of watches for both fitness and medical purposes—are growing segments augmenting input to big data analytics of the IoT. Li-ion is the dominant choice for these small form factor markets due to its higher specific energy (Wh/kg), lower cost, and flexible form factors, all of which are driving the demand for smaller Li-ion chargers. onsemi has industry-leading technology for Li-ion chargers in extremely small footprints to enable the migration to smaller charging form factors.
Li-ion CC/CV Charge Profile
Li-ion typically implements the constant current (CC)/constant voltage (CV) charge profile. Moving from left to right, an empty cell begins charging with a gentle charge (~C/5), or the “pre-charge.” Li-ion prematurely ages if too much current is applied when near empty. Once the cell voltage rises to VBATMIN (typically 3.6V for cobalt), then it is safe to enter CC mode, with the maximum allowable charge current specified in the cell data sheet (~1C). This maximizes the Time to Charge (TTC). When the cell voltages reach VFLOAT, or the maximum voltage specified in the cell datasheet, the charger then enters CV mode. CV mode clamps the voltage and the current entering the cell naturally tapers as the cell approaches full charge. Finally, as the tapering charge, current approaches C/10 to C/20 the charger terminates the charge.
The values for VFLOAT, VBATMIN, IPRE and IFAST, can be found in the battery datasheet. Many Li-ion chargers require a companion processor to program its internal registers across I2C in order to produce the CC/CV charge profile. onsemi’s FAN54120 stand-alone Li-ion charger autonomously executes the CC/CV Charge profile, without any I2C registers, or firmware. This eliminates the need for a companion processor, thus reducing cost, space and complexity. It simply works out of the box, reducing time to market. Because there is no firmware, the FAN54120 is tamperproof, another advantage for security-sensitive applications like medical or IoT.
The FAN54120 standalone charger is an extremely low form factor. Now available in a 2mm x 2mm DFN package, and a soon to be released, 1.36mm x 0.76mm WLCSP package.
FAN54120 500mA Linear Stand-Alone Charger
The FAN54120 references an external rset resistor to autonomously produce the CC/CV charge profile across a wide range of battery capacities. For example, if the cell can handle 500mA maximum charge, by choosing a 1kΩ rset (IFAST=500mA), the FAN54120 will automatically pre-charge at 100mA (IFAST/5), a transition to 500mA (IFAST) for CC mode, and then terminate the charge @ 50mA (IFAST/10), for a 750mAh battery.
For smaller Li-ion battery capacities like 140mAh, a 5KΩ reset resister results in a 20mA pre-charge, 100mA CC Mode charge current, and a 10mA charge termination.
The FAN54120 supports JEITA “Safe-to-Charge” temperature operation with an external NTC. The FAN54120 tolerates a maximum 28V input voltage, while operating up to 6V input, and exhibits a world-class quiescent current of only 150nA. This ensures the FAN54120 will not over-discharge the cell in between charges. Finally, the FAN54120 offers 0.5% CV accuracy preventing inadvertent OVP (Over Voltage Protection) tripping of less expensive cell protection circuits with + 50mV tolerance.
Markets and applications include earbuds, wearables, Bluetooth speakers and headsets, IoT devices, mini and micro drones, cameras, E-cigarettes, toys and games.
See related product
