The wearables part of the IoT requires some special expertise. First, the devices usually have to be very small and lightweight. And then they have to be battery-operated, very easy to recharge (unless it uses a primary battery), and they must have a fairly long battery operate time. Conflicting requirements are certain. Wireless battery charging may just be the key technology for this application area.
The combination of STMicroelectronics STWBC-WA charging-transmitter controller and STWLC04 wireless battery-charger receiver ICs enables wireless power transfers up to 1 W. The system uses inductive coupling, with coils required for this power transfer just 11 mm in diameter on the receive side and 20 mm for the transmit side — allowing slimmer form factors. The coupling takes place over a distance up to a few millimeters and uses a 110- to 205-kHz frequency.
The STWLC04 is an integrated wireless power receiver suitable for wearable applications. The chip is focused on 1-W power transfer based on Qi protocol with digital control and precise analog control loops ensuring stable operation. The power transmitter unit is responsible for controlling the transmitting coil and generating the correct amount of power requested by the receiver unit. The device has a high-efficiency synchronous rectifier, and 800-kHz programmable step-down converter with efficiency of up to 90%. It uses a simplified Li-ion/polymer charger function and a 32-bit, 16-MHz MCU with a 16-Kbyte ROM and 2-Kbyte RAM. The IC comes in a 3.12 x 4.73-mm flip-chip package.
The STWBC-WA digital controller IC for wireless battery charger transmitters uses a cost-effective half-bridge output topology with integrated drivers (optional full-bridge configuration for 3-W applications). The chip's input supply range is 3 to 5.5 V and it has 32 Kbytes of program memory flash and 1 Kbyte true data EEPROM for data, plus 6 Kbytes of RAM. It comes in a VFQFPN32 package.
STMicro is a member of the Wireless Power Consortium and both ICs fit to the Qi specification. Both chips operate over −40°C to 105°C and a full reference design is available. The STWBC-WA costs $3.63 ea/1,000 and the STWLC04 $1.81 ea/1,000. Available right now.
A video about wireless power transfer is available here: https://www.youtube.com/watch?v=VJfVhrSLm-E
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