Introduction The STEVAL-ISB68WA is an evaluation kit based on STWLC68JRH wireless power receiver and it is designed as reference solution for wearable applications. The kit consists of a wireless receiver module and USB-to-I2C bridging dongle. The receiver is a 3-elements stack: a PCB housing the STWLC68JRH wireless power receiver and all the required external components, a 2 mm thick plastic spacer and a 15 mm diameter receiving coil facing the bottom side.
UM2693 Wireless power receiver module Wireless power receiver module Overview As visible in Figure 2, the schematic diagram of the wireless power receiver is relatively simple. The RX coil (J1- J2 terminal) is part of the series resonant circuit (C1 through C4 capacitors) that provides the AC voltage to the AC1-AC2 pins of the STWLC68JRH.
UM2693 Wireless power receiver module The terminals for the receiving coil, the output load and the control signals are summarized in Table 1. The output rail and the control interface are already made easily accessible by means of wires terminated with pin header female connectors (Figure Table 1.
UM2693 Wireless power receiver module Figure 4. Receiver module wiring Additional control signals and programmable general-purpose I/O pins are available at the STWLC68JRH, but they are not used in the module to keep the reference solution as simple as possible. The STWLC68JRH chip can handle up to 400 kHz speed over the I2C bus.
UM2693 Wireless power receiver module As already mentioned, a LED (D3) is connected to GPIO0 and it is used as output state monitor: it turns-on when a correct power transfer is established between the receiving module and the transmitter, and the output voltage is enabled.
UM2693 USB to I2C bridging dongle USB to I2C bridging dongle Overview The USB to I2C bridging dongle is the tool that allows interfacing the receiver to the Graphical User Interface running on a PC. The P2 connector signals are summarized in Table 4.
UM2693 USB to I2C bridging dongle Signal Description Auxiliary supply rail. Used to supply the STWLC68JRH chip via VOUT when the receiver module is not placed on a transmitter. The D4 diode (see VBUS Figure 6) avoids backflow toward the USB supply rail when VOUT is higher than 5V.
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UM2693 USB to I2C bridging dongle Component Value Description Part Number Manufacturer Pin header, 2.54 mm pitch 3.3V, 100 mA, Linear LD2981CM33TR STMicroelectronics regulator, SOT23-5L Fuse, 0.25A, 0603 0603L025 Littelfuse USB to I2C MCP2221A-I/ML Microchip converter, QFN16 Linear regulator, 3.3V, 100 mA, LD2981CM33TR STMicroelectronics SOT23-5L...
STEVAL-ISB68WA test setup STEVAL-ISB68WA test setup The evaluation of the STEVAL-ISB68WA kit relies on a suitable wireless power transmitter that could mate with the coil of the RX module. A good coupling factor is essential for both power transfer efficiency and data communication reliability between the transmitter and the receiver.
UM2693 STEVAL-ISB68WA test setup Figure 9. Configuration of the transmitter As soon as the LED on the receiver lights up, its control GUI can be launched. Connectivity with the STWLC68JRH is automatically verified and the chip info (IDs content) is shown in the registers page (Figure 10).
UM2693 STEVAL-ISB68WA test setup Figure 10. Graphical User Interface registers page showing chip IDs To monitor the operation of the receiver, a real-time plotting of key parameters can be selected: in Figure 11 VRECT and VOUT voltages, the temperature of the rectifier (TRECT) and its output current (ISNS) are shown.
UM2693 STEVAL-ISB68WA test setup The load at VOUT can be increased up to 2.5 W. A 10 Ω purely resistive load (i.e. 2.5 W load at 5 V) is usually managed without problems also at ping-up. In some case (e.g. a following DC-DC converter stage) the load could show a remarkable capacitive behavior and a relatively high initial current may trigger the over-current protection or may exceed the dynamic capability of the transmitter.
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