Fast Charging Q&A with SiBreeze Technologies CEO Sridhar Kotikalapoodi

SiBreeze Technologies Fast Charging

CEO Sridhar Kotikalapoodi talks about SiBreeze Fast Charging with 10X smaller inductor and DCR values


Q: Congratulations on the Si117 Silicon Launch

Sridhar: Thank you. Working on the Si117 silicon, featuring our ground breaking SLIM SWITCHER® and BEST SWITCHER™ technologies has been an exciting experience. Inductor value and thickness have been a big limiting factor for power supply speed, form factory, battery life and thermals. Now with the release of our Si117 silicon, one can validate our technologies resulting in industry’s first and only silicon with 10X reduction in inductor and DCR (effective inductor DC resistance) values, 5X increase in speed and 3X inductor current capability – all these at the same switching frequency.

Q: Does SiBreeze fast charging technology require master-slave configuration for mobile device fast charging?

Sridhar: Our fast charging technologies could provide significantly decreased charge times and thermals independent of the charger topology, whether through a stand-alone single die, single inductor charger or through a master-slave dual inductor charger configuration.

Presently most fast charging solutions based on standard switch mode configuration use a 1uH inductor. The DCR of the inductor limits the fast charging currents to 3 Amps to 3.5 Amps range, thus limiting the achievable fast charging to about 10 Watts to 12 Watts with a single inductor.  Furthermore, since the switching frequency is about 1.5MHz or so, there is significant AC ripple with 1uH inductor resulting in significant AC losses as well in the inductor.

In the standard topology fast chargers, Inductor DCR cannot be reduced by increasing inductor thickness (form factor limitation) or by reducing inductor value ( inductor ripple, inductor current saturation and AC loss limitation). Therefore, traditional fast chargers need to use master-slave configuration to get fast charging beyond 12 Watts ( 3 Amps) or so.

When SiBreeze fast charging technology is used in master-slave charging configuration, the DCR of both master and slave inductors are decreased by a factory of 10X. In addition, because the inductor value is reduced by 10X, it’s value is not limited by it’s thickness anymore. Therefore, one could choose the inductor value to tremendously reduce inductor current ripple, thus reducing the inductor AC losses. With both Inductor DC and AC losses optimized, one could get tremendously increased charge currents with decreased thermals and charge times by replacing a standard master-slave charger with a master-slave charger based on our technologies.

In addition, fast chargers based on SiBreeze technologies extend fast charging capabilities achievable with single die, single inductor solutions significantly. Fast chargers based on our technology with 10X smaller inductor and DCR values, could provide up to 3X inductor currents for same inductor temperature rise, thus tremendously increasing the fast charging achievable with a single die, single inductor solution up to 20 Watts and beyond.

In summary, fast charging solutions based on our technologies could achieve significantly decreased charge times with faster charging and decreased thermals in much smaller foot print by replacing standard master slave chargers with our technology based master-slave chargers. Furthermore, solutions currently using single inductor based standard fast charging could tremendously increase fast charge capability with out switching to master slave configuration by using our technologies and thus significantly reducing the total BoM and PCB volume compared to a dual die / dual inductor solution.

Q: How does SiBreeze Technologies fast charging compare to Direct Charging and Inductor less switched capacitor based charging?

Sridhar: Direct Chargers, even though the charger is outside the phone (i.e. in the wall adapter), still need a switch inside the phone to sense and limit charge currents, etc. This switch is carrying the entire charge current all the time compared to a switch mode charger, wherein, even though there are two switches instead of one, each switch on average carries only partial charge current with average currents of both switches adding up to the total charge current. Therefore, compared to a direct charger, the standard switch mode charger, as the switches are carrying only partial currents on average, dissipates about same heat for same total switch size . However, standard switching chargers have additional losses due to inductor DCR, thus limiting charge currents compared to a direct charger. Master slave switching charger tries to minimize this limitation to some extent by splitting the current across two inductors with each inductor carrying only half the current, thus reducing DCR drop by half. However, since with our fast charging technologies the inductor DCR could be reduced by a factor of 10X, the drop across the inductor is virtually eliminated (smaller then the output voltage step size resolution of the direct chargers), therefore, the total dissipation being similar to a direct charger wherein the actual charger is outside the phone.

Further, since direct chargers, unlike switch mode chargers, don’t provide current multiplication for charge currents, they need to carry entire charge currents through the charger cable, thus requiring a more expensive cable.

In addition, since there is no charger IC in the phone, direct chargers need to adjust the wall adapter output voltage continuously in real time to track the battery voltage with even few tens of milli-volts deviation from the required ideal tracking voltage causing either significantly decreased charge currents or significantly increased thermals. Battery voltage measurement accuracy, wall adapter output voltage accuracy and step size, delays in adjusting the wall adapter output voltage (as the AC/DC loops have very limited bandwidths) to track dynamic battery voltages in real time continuously – all affect the charge current accuracy and could limit the charging speed or increase the thermals.

In addition, direct chargers still need the main charger for wireless charging, dead battery charging etc. and in addition cannot share fast charge currents with the main charger, thus wasting precious phone real estate.

Chargers based on our topology do not have these limitations. Since there is a current multiplication like standard switch mode charger, these could provide fast charge currents with standard cable. Chargers based on our technologies work from wide range of adapter output voltages and unlike direct charges, our chargers don’t need wall adapter output to track battery voltage continuously for charger current accuracy or thermal limitations and could operate even from fixed voltage USB power delivery adapters resulting in much more reliable charge currents, thermals and smaller wall adapters.

Furthermore, single charger could support all the charging including wireless charging, pre-charging, fast charging etc thus providing a complete safe and reliable fast charging solution with a much smaller Bill-of-Materials and phone real estate.  In addition, fast charge currents could be shared with the main charger if additional charger is present resulting in much cooler temperatures and more efficient use of the main charger than the direct charging solutions.

Comparison with inductor less charge pump based chargers is similar to the comparison with direct charges. Charge pump based chargers try to overcome the current multiplication limitation of direct charges with switched capacitor charge pumps.

Therefore, in summary, chargers based on our technologies could achieve efficiencies and charge speeds comparable to what theoretically possible with direct chargers with out requiring expensive charger cables and with increased reliability and smaller wall adapters as ours don’t need continuous fine tuning of the wall adapter voltages to track battery voltage and therefore providing an ultimate charging experience, irrespective of adapter voltage accuracy, battery and adapter voltage measurement accuracy, dynamic loads on the battery etc.

Q: Interesting discussion on fast charging. What other applications are SiBreeze’s technologies applicable?

Sridhar: Our technologies are applicable to power supplies in a wide range of applications, whether for reducing energy wastage in data centers or for enabling slimmer form factor devices with increased battery run time in mobile, notebook and Internet of Things (IoT).

Power intensive AI processors need more intelligent power delivery. Multi-core CPUs with increased dynamic range and swings in CPU supply voltages, due to increased vectorized instructions, need a multi core supply with dynamic power-on-demand capabilities.  Our technologies, with 10X smaller inductor value and 5X bandwidth at the same switching frequency, tremendously facilitate these, thus increasing system efficiency and battery run times compared to the present standard implementations.

In addition, 10X reduction in inductor DCR enables decreased losses across other power supplies in the system like back-light boost converter etc resulting in further improvements in system efficiency and battery run time.

In space limited IoT applications, due to inductor size limitations, charge pump based power supplies are presently being used which severely impact battery life and system efficiency. With 10X reduced inductor values, our technologies enable the use of more efficient inductor based power supplies in applications where it wasn’t possible earlier due to inductor size limitations.

Furthermore, for space constrained micro-module applications where in inductor and capacitors are co-packaged with the power supply IC, our technologies facilitate tremendous reduction in the form factor of the micro module.


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