Renesas Electronics has unveiled a new 30W wireless charging receiver chip, which is designed to fit into Qualcomm’s Snapdragon 5G Mobile Platform. Renesas said its P9412 enables Qualcomm to be the first to offer a fast 30W wireless charging option to 5G mobile handset designers.
Renesas’ P9412 supports proprietary fast charging modes with authentication and 24kB multiple-time programmable (MTP) non-volatile memory.
In an interview with EE Times, Amit Bavisi, vice president and general manager of Renesas Wireless Power Group, said “The 5G revolution challenges mobile handset designers, since the technology is higher performance and enables broader and perhaps, more power-hungry user applications than its predecessors. As handset manufacturers increase their 5G device lineup while also expanding battery sizes and packing more and more features into these smartphones, wireless power design demands high-efficiency fast charging with a lower thermal footprint,” said Bavisi.
Wireless charging for 5G
A wireless charging system has a wireless power transmitter base station with one or more transmitters that make power available via DC-to-AC inverters and transmit the power to a pair of inductors in a mobile device. A typical system employs near-field magnetic induction between the coils and can be a free positioning or magnetically driven system. The receiver controls the transferred power in order to optimize charging. Rx-to-Tx communication uses existing power links via in-band communication of the transmission frequencies or also supports out-of-band communication.
“Wireless power design involves both hardware and software; it is no doubt a system play. To achieve a stable and high-performing wireless power solution, a good design must have solid hardware quality and a robust software algorithm. These go hand in hand: Wireless power is truly an SoC where hardware and software interplay to create a perfect system solution and the scalability necessary for solving various dynamic user scenarios,” said Bavisi.
The wireless technology is well-known, but the design of transmitters, their location, the possibility of maximizing efficiency, and validating the behavior of the entire system represent complex challenges that require the use of complex engineering solutions.
Qi is a wireless charging system that uses electromagnetic induction. In the transmitter or base station, which is usually a flat surface, a coil passed through by a variable electric current generates an oscillating electromagnetic field. In the object to be charged, a similar coil detects this variable field and, due to the well-known laws of electromagnetism, a current flows through it, which then supplies the battery to be charged.
“The antennas are generally customized to deliver the best fit for wireless receiver devices in the end device’s form factor. Generally speaking, it’s common to see antennas with 40mm-50mm diameter used in phones,” said Bavisi. Qi, for example, provides for various configurations of coils within wireless chargers so that users are not forced to precisely position the devices to be charged. In theory, the coils need to be close together to transfer power, ideally overlapping, but some elements of the Qi standard allow charging even if the coils are a few centimeters apart ). The standard also provides for a form of communication between the charger and the charged device: this is done using the same magnetic field as the charge and allows, among other things, the generation of the magnetic field to be stopped when the charge is complete.
The reference designs aim to provide turnkey solutions to facilitate smartphone OEMs to quickly and cost-effectively deploy fast wireless charging on high-end and mid-range smartphones, with multi-time programmability (MTP) and OTA updates to simplify software development and the Qi certification process. Bavisi highlighted how Renesas’ 30W solution with Qualcomm Technologies’ 5G solution offers over 85% end-to-end system efficiency, facilitating fast wireless charging technology delivery to the next generation of mid-range smartphones.
The wireless power receiver includes Renesas’ P9412 with an integrated high-voltage capacitor divider, offering small size and freeing up PCB area to include new features. P4912 is a full synchronous rectifier with low resistance switches with an embedded 32-bit ARM Cortex-M0 processor.
“The integrated cap divider greatly improves system efficiency while reducing the solution size for high-power designs. By integrating a high-efficiency cap divider (>98%), the wireless power receiver coil now operates at half of the current level, which drastically reduces the overall power losses. The integrated solution allows the wireless receiver IC to seamlessly control the state transitions during operational mode changes and simplifies the system design as well. To achieve 85-90% end-to-end system efficiency (wall adapter to wireless power output into the phone battery or battery charger), the efficiency of individual components needs to be high so as not to create hotspots. A high-efficiency cap divider at 20V (fully integrated) reduces the integration problem for phone customers and computer customers, and will make it compatible to the traditional battery charging architectures,” said Bavisi.
The P9412 operates in accordance with the WPC (Wireless Power Consortium) 5W specification and also employs higher power protocols that allow power delivery to be extended beyond the WPC 5W standard. A customized high-power protocol is embedded in the device’s firmware, allowing the system to authenticate power transfer beyond 15W. (Figure 2).
The wireless energy is stored on one or more capacitors connected to VRECT. The rectifier circuit and control block provide conversions and connections to maintain efficiency at required levels. An internal ADC monitors the voltage at VRECT and the load current, and P9412 sends instructions to the power transmitter to increase or decrease the amount of power transferred.
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