STWBC-WA/STWLC04 chips enable 1 W power transfer with small coils, high efficiency

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 for certain. Wireless battery charging may just be the key technology for this application

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 mm 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-watt 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 chips 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

STMicro is a member of the Wireless Power Consortium and
both ICs fit to the Qi specification. Both chips operate over -40° 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.