ST STEVAL-WLC38RX User manual

Introduction
The STEVAL-WLC38RX evaluation board is based on STWLC38 and is designed for wireless power receiver applications. It
allows users to quickly start their 5W Qi-BPP and 15W Qi-EPP compatible wireless charging receiver projects.
The STWLC38 wireless power receiver can manage up to 15 W of power according to the Wireless Power Consortium’s
Extended Power Profile (EPP).
The integrated circuit requires only a few external components and offers high design flexibility. Using an on-board USB-to-I2C
bridge, the user can monitor and control the STWLC38 using the STSW-WPSTUDIO graphical user interface (GUI).
STEVAL-WLC38RX includes several safety mechanisms providing overtemperature (OVTP), overcurrent (OCP) and
overvoltage (OVP) protections as well as foreign object detection (FOD) for reliable designs.
Figure 1. STEVAL-WLC38RX evaluation board
Getting started with the STEVAL-WLC38RX wireless power receiver evaluation
board for 5 W Qi BPP and 15 W Qi EPP applications
UM3154
User manual
UM3154 - Rev 2 - September 2023
For further information contact your local STMicroelectronics sales office. www.st.com

1 Get started
To get started with STEVAL-WLC38RX, you will need the following items to use the reference design kit:
• Evaluation kit components:
–STEVAL-WLC38RX board
• Additional hardware
–STEVAL-WBC86TX for the best results for a 5 W turnkey wireless charging system or any other Qi
BPP or Qi EPP compliant transmitter available on the market
– Electronic load
– Windows PC for measurements and configurations
• Software:
–STSW-WPSTUDIO Wireless Power Studio PC GUI installation package
– I²C drivers
• Application notes:
– Coil selection guide: AN5961
– GUI guide: UM3164
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Get started
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2 Reference design specifications
Target specifications of STEVAL-WLC38RX evaluation board are as follows:
Table 1. reference design specifications
Parameter Description
Qi compatibility Qi 1.3 BPP and EPP protocol
Rx application PCB area 24 mm x 34 mm
Rx coil specifications Inductance 8 uH, DCR 190 mΩ, ACR 225 mΩ
Dimensions 57 mm x 57 mm x 0.42 mm (LD81FP008-1H)
Output voltage (Vout, continuous
operation) 5 V Baseline Power Profile / 9 V Extended Power Profile
Output current (Iout, Load) Recommended current load range is 0.1 – 1 A
Host MCU STM32 used as a reference, the reference I2C driver can be ported to any other
MCU family
USB-to-I2C converter Embedded in the evaluation board
Efficiency 77.6% (5 W operation) with STEVAL-WBC86TX
81% (peak efficiency) with STEVAL-WBC86TX at 3 W
Applicable charging gap between Tx
and Rx coils(z-distance)
3 – 13 mm (5 W output) with STEVAL-WBC86TX transmitter,
maximum 16 mm – stable communication without output enabled
Misalignment between Tx and Rx coils
(x-y offset from the center) 12 mm for 5 W output, 18 mm for stable communication without output enabled
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Reference design specifications
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3 Overview of the Board
The STEVAL-WLC38RX evaluation board is optimized for performance. The board features:
• STWLC38 wireless power receiver chip with BPP and EPP compliant firmware
• Very few external components, optimized BOM and PCB space
• On-chip high efficiency rectifier
• Support for external NTC for thermal monitoring
• On-chip thermal management and protections
• WPC Qi extended power profile (EPP, 15 W) compatible receiver chip
•On board USB-to-I2C converter
• USB Type-C® connector for PC GUI connection
Figure 2. Main board elements
• Series resonant capacitors and the receiving coil together form a resonant circuit. This circuit is in charge
of receiving the power signal, so any components/tracks involved should be rated accordingly
• USB/I2C converter–provides a communication channel between a PC and STWLC38. LED D8 (Red)
indicates that the I2C converter is powered, D9 (yellow) indicates that STWLC38 is connected to the GUI.
LED D10 (Green) indicates that I2C communication was initialized and is ready. Switch S1 resets the
converter. Note that header P3 connects the converter’s I2C signals to the STWLC38 I2C signals. Short the
corresponding pins with a jumper to establish a connection between the two ICs.
• Red LED (D7)–indicates STWLC38 core power status (LED is on when the core is powered).
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Overview of the Board
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3.1 Test points
STEVAL-WLC38RX features several headers and test points to provide easy access to key signals.
Figure 3. Headers and test points
Table 2. header and test point descriptions
Connector Name Description
P1 Rx Coil 4-pin Header: for mounting External RX Coil:
Pin 1,2 AC2; Pin3,4 AC1_COIL
P3 I2C2x4 pin Header: AGND, SDA, SCL, INTB
P6 Control signals 8 pin Header: Programmable GPIOs, ENB, INTB, NTC
P4 VRECT 2-pin Header: VRECT output
P5 VOUT 4-pin Header: VOUT output
P7, P8, P14 GROUND 2-pin Header: Ground connection
P9, P10 GROUND 4-pin Header: Ground connection
P11 VBUS-VOUT 2 Pin Header: VBUS to VOUT Wire Jumper
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Connector Name Description
J1 USB-C USB-C Connector
3.2 Basic operating modes
The receiver generally works in two modes - DC (also called Standalone) mode and AC mode.
DC mode is characterized by the wireless receiver being powered from a DC power supply such as external
power supply or USB. This mode is used for Patch and Configuration loading (described later ). Before entering
this mode, device shall not be powered from power transmitter (device is put away from power transmitter or
power transmitter is being powered off).
AC mode is used when the wireless receiver is powered from a wireless power transmitter. A stable and ongoing
power transfer between the transmitter and the receiver is indicated by LED (D7). Make sure that Rx is not
powered by external DC power before entering this mode.
3.3 Functional check
Figure 4. Transmitter and receiver boards setup
The first sign of an ongoing power transfer is the D7 LED, as this LED indicates the internal power supply of the
device is ready. A continuously shining LED indicates a stable power supply, while a blinking or inactive LED
indicates an unstable and/or insufficient power supply.
The LED D7 is permanently OFF means there is no power transfer between the transmitter and the receiver.
Check if the power supply of the transmitter is connected and working properly. Power transfer termination may
also be caused by a large enough misalignment (from an ideal center-to-center position) between receiver and
transmitter coils. This issue is, to a certain degree, mitigated by an [ARC mode] feature, which improves spatial
freedom of the charging.
The LED D7 is blinking means some power is transferred, but the amount is insufficient, or the transfer is
unstable. One of the reasons for such instability may be communication issue between the power transmitter and
the power receiver. The instability may as well be caused by one of the protections (OVTP, OCP, OTP) being
triggered.
The built-in USB-I2C converter features three LEDs. LED D8 (RED) indicates presence of power from the USB
connector (J1). LED D9 (YELLOW) indicates that STWLC38 is connected to the GUI. LED D10 (GREEN)
indicates that I2C communication was initialized and is ready.
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Basic operating modes
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4 Graphical user interface (GUI)
STWLC38 (and other ST wireless charging devices) can be configured using the STCHARGE Wireless Power
Studio GUI (STSW-WPSSTUDIO). The GUI can also be used to control, monitor and program the device.
For more information, please see STCHARGE Wireless Power Studio User Manual.
4.1 Connecting STWLC38 to PC GUI
Step 1. Connect the board to a PC by plugging a USB-C cable into the connector J1.
Make sure the STWLC38 I²C pins are connected to the USB-C connector. This can be done by
shorting the appropriate signals (SDA, SCL, INT) on header P3.
Step 2. Power on the STWLC38 before connecting to the GUI, this can be done in one of the following ways:
Step 2a. Place it onto a power transmitter. The device operates in Rx mode.
Step 2b. Switch it into DC mode by connecting a DC power supply to the STWLC38 VOUT pin. The
voltage must be no higher than 3 V.
Step 2c. Switch it into DC mode by connecting the STWLC38 vout signal to the VBUS pin of the
converter board.
Note: Please note that the Rx registers will be available only if the device is operating in Rx mode, DC
mode is mainly used for updating patch and configuration file.
Step 3. Power up the board and open the GUI on your PC. Click the [Connection] button in the top menu.
Up to two devices can be connected at a time. This allows the user to control both Rx and Tx at the
same time).
Figure 5. PC GUI main screen
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Graphical user interface (GUI)
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Step 4. Select [WLC38] as the Rx and click the [Connect] button on the right side of the window.
Figure 6. Device selection and connection
4.2 Patch and configuration files
Firmware of the device can be updated using a Patch file (a binary file in .memh format). The latest version of the
Patch can be found at STWLC38. Updating the firmware is not required but may improve the performance of the
board.
The device can be configured using a Configuration file, a binary file containing settings of all registers which can
be found in the GUI. The GUI can also be used to generate a custom Configuration file, making it easier to quickly
change configuration of the board and/or transfer the configuration to another board.
In GUI, registers are divided into two groups. The value changes of registers colored in RED will take effect only if
a configuration file is generated and written to the device. Changes of registers colored in BLACK will take effect
immediately and can be saved to the configuration file. During power-up, the values of those registers are set to
the values defined in the configuration file written on the device. Registers that cannot be saved to the
configuration file and whose value is lost upon reboot have this fact noted in the description.
4.3 Configuration file generation
Using the STSW-WPSTUDIO makes generating the Configuration file quite simple.
Step 1. To make sure that the latest values are shown in the GUI, it is recommended to use the [Read
[Rx]WLC38] button to dump values from the device to the GUI. Then, the required changes of the
register may be made. This should be done, especially when going from DC mode to Rx mode.
Step 2. Click the [Write [RX]WLC38] button to save current configuration to temp memory.
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Patch and configuration files
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Step 3. Click the [Save RX] button in the RX Registers tab or the Common registers tab.
Figure 7. Save RX button
Step 4. Enter a Configuration ID number (used for version control) and press [OK].
Figure 8. Configuration ID field
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Step 5. Choose your location for the save file.
After choosing a location, the configuration will be saved as a .memh file in the selected folder.
Figure 9. Save folder selection
4.4 Header file
The GUI can also be used to generate a Header file, a binary .h file containing both Configuration and Patch files.
The Header file makes programming the device using a host MCU easier, as both Configuration and Patch can be
loaded at once by simply including the Header file in the host code.
4.5 Header file generation
A custom Header file can be generated in the Header Generator tab.
Step 1. Start by selecting [WLC38] in the top menu.
Figure 10. Device selection
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Header file
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