ST STEVAL-WBC86TX User manual

Introduction
The STEVAL-WBC86TX evaluation board, based on the STWBC86, is designed for wireless power transmitter applications and
allows its users to quickly start their 5 W Qi BPP wireless charging projects.
The STWBC86 wireless transmitter IC can deliver up to 15 W (coil dependent), however this reference design document is
limited to only provide sufficient information to develop a project for up to 5 W charging compatible with Qi 1.2.4 Baseline Power
Profile (BPP) power transfer by Wireless Power Consortium’s inductive wireless power technology.
The integrated circuit requires only a few external components and can work with 5-20 V input voltage.
Using an on-board USB-to-I2C bridge, the user can monitor and control the STWBC86 using the STSW-WPSTUDIO graphical
user interface (GUI).
The STEVAL-WBC86TX includes several safety mechanisms providing overtemperature (OTP), overcurrent (OCP), and
overvoltage (OVP) protections as well as foreign object detection (FOD) for reliable designs.
Figure 1. STEVAL-WBC86TX board
To get started with the STEVAL-WBC86TX, the following items are needed to use the reference design kit:
• Evaluation kit components:
– STEVAL-WBC86TX board
Getting started with the STEVAL-WBC86TX wireless power transmitter evaluation
board for up to 5 W Qi-BPP applications
UM3161
User manual
UM3161 - Rev 1 - July 2023
For further information contact your local STMicroelectronics sales office. www.st.com

• Additional hardware:
– USB adapter 5 V / 3 A or power supply
– 2 x USB Type-C® cables (one can be replaced with either 2.1 mm jack or pin cable)
– Windows PC
• Software:
–STSW-WPSTUDIO Wireless Power Studio PC GUI installation package
– I2C drivers
• Application notes:
– GUI guide: UM3164
Begin by installing both the I2C drivers and the STSW-WPSTUDIO GUI. Visit the ST website for additional information regarding
the STSW-WPSTUDIO GUI.
Connect a 5 V power supply to power the board using either the USB Type-C®, jack, or pin cable. Using a jumper, select the
chosen method of power delivery on header P1.
Using a USB Type-C® cable, connect the board to the PC (connector P4 on the board). This allows the user to communicate
with the board - program it and monitor its function.
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1 Reference design specifications
The target specifications of the STEVAL-WBC86TX evaluation board are as follows:
Table 1. STEVAL-WBC86TX target specifications
Parameter Description
Qi compatibility Qi 1.2.4 compatible
Tx application PCB area 40 mm x 24 mm
Tx coil specifications Inductance 6.3 uH, DCR 20 mOhm, ACR 20 mOhm @ 100 kHz, dimensions 53.3
mm x 53.3 mm x 6 mm
Qi Tx topology A11a
Input voltage (Vin) 5 V
Input current (Iin) 1.5 A
Host MCU STM32 used as a reference, the reference I2C driver can be ported to any other
MCU family
USB-to-I2C converter FT260, embedded in the evaluation board
Efficiency 77.6 % (5 W operation) with STEVAL-WLC38RX
81 % (peak efficiency) with STEVAL-WLC38RX at 3 W
Applicable charging gap between Tx
and Rx coils
(z-distance)
3 – 13 mm (5 W output) with STEVAL-WLC38RX receiver,
maximum 16 mm – stable communication without output enabled
Operational modes Transmitter only
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Reference design specifications
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2 Overview of the board
The STEVAL-WBC86TX evaluation board is optimized for performance. The board features:
• STWBC86 wireless power transmitter chip with BPP 1.2.4 compatible firmware
• Very few external components, optimized BOM and PCB space
• On-chip high efficiency full bridge inverter
• 32-bit, 64 MHz Arm® Cortex® microcontroller with 8 KB SRAM
• 9-channel, 10-bit A/D converter
• On-chip thermal management and protections
• Foreign object detection (FOD) function
• I2C interface for communication with host system (optional)
• On-board USB-to-I2C converter
• Chip scale package (CSP), ROHS complaint
Figure 2. STEVAL-WBC86TX evaluation board features
• Series resonant capacitors (Ctank) and the transmitting coil form a resonant circuit. This circuit is in charge
of transmitting the power signal, so any components/tracks involved should be rated accordingly.
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Overview of the board
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• CBT1 and CBT2 are bootstrapping capacitors, which ensure the proper functionality of the integrated
inverter. This should be considered during PCB design, as these nets generate noise and should therefore
be routed separately from sensitive circuits.
• ASK demodulation circuit - apart from transferring power, the power signal is also used for receiver to
transmitter communication. The communication signal is extracted from the power signal using the ASK
demodulation circuit and fed into the VS pin of STWBC86 for processing. For further details, refer to
Section 4.12.1 ASK communication.
• USB/I2C converter - provides a communication channel between a PC and STWBC86. LED D6 (red)
indicates the I2C converter is powered, D4 (yellow) indicates that STWBC86 is connected to the GUI. LED
D5 (green) indicates the I2C communication was initialized and is ready. Switch S1 resets the converter.
Please note that header P2 connects the converter’s I2C signals to the STWBC86 I2C signals. Short the
corresponding pins with a jumper to establish a connection between the two ICs.
• Power input (USB Type-C® connector/jack/pin header) - 3 separate inputs can be used to power the board,
but only one is used at a time. Therefore, it is necessary to select the input using a jumper on header P1.
• Red LED (D3) - connected to GPIO0, can be configured to signal various conditions (power ready,
communication active etc.).
2.1 Test points
The STEVAL-WBC86TX features several connectors and test points to provide easy access to key signals.
Figure 3. Connectors and test points
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Test points
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Table 2. Connectors and test points
Connector / test point Name Description
VIN VIN Input voltage (power pins)
VINV VINV Inverter voltage pins
P2 I2C SDA, SCL, INT, and RST signals for I2C communication
P14 Digital interface I2C, GPIO, and RST signals
TP1 Ring node Ring node
TP2 VIN STWBC86 input voltage sensing
TP3 AC2 Resonant circuit terminal
TP4 AC1 Resonant circuit terminal
TP5 VINV STWBC86 inverter voltage sensing
TP6 V1V8 STWBC86’s 1.8 V LDO output
TP7 GND Ground
TP8 VS VS signal sensing
2.2 Basic operating modes
The STWBC86 is designed to work in transmitter mode only. Once the board is powered up, the device
automatically starts pinging (if enabled), which means it starts scanning its power transfer interface for a potential
power receiver. Once a suitable receiver is found, the STWBC86 initializes power transfer. After the receiver is
removed from the interface, the device returns to the pinging phase.
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Basic operating modes
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3 Graphical user interface (GUI)
The STWBC86 (and other STMicroelectronics wireless charging devices) can be configured using
STMicroelectronics’ STCHARGE Wireless Power Studio GUI. The GUI can also be used to control, monitor, and
program the device.
For more information, please see the UM3164.
3.1 Connecting STWBC86 to PC GUI
Connect the board to a PC by plugging a USB Type-C® cable into the connector J3. Make sure the STWBC86
I2C pins are connected to the USB Type-C® connector. This can be done by shorting the appropriate signals
(SDA, SCL, INT) on header P2. 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).
Select WBC86 as the Tx and click the Connect button on the right side of the window.
Figure 4. GUI connection
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Graphical user interface (GUI)
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Figure 5. GUI device connection
3.2 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 on this [ST website]. Updating the firmware is not required but may improve 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.
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Patch and Configuration files
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3.3 Configuration file generation
Using the STSW-WPSTUDIO makes generating the Configuration file quite simple – the user can do so by
clicking the “Save TX” button in the TX Registers tab or the Common Registers tab, entering a configuration ID
number (used for version control) and pressing OK. The GUI then asks for a save destination. After choosing a
location, the Configuration is saved as a .memh file in the selected folder.
Figure 6. Generation of configuration file
Figure 7. Version of the configuration file
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Configuration file generation
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Figure 8. Saving of the configuration file
3.4 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 IC easier, as both Configuration and Patch can be
loaded at once by simply including the Header file in the host code.
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Header file
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3.5 Header file generation
A custom Header file can be generated in the Header Generator tab. Start by selecting WBC86 in the top menu.
Figure 9. Header generator - chip selection
Continue by selecting the Patch and Configuration file and press Generate. A pop-up window appears, asking to
confirm the correct Patch version has been selected.
Figure 10. Header generation - pop up window
After confirming the Patch version, the GUI asks for a save destination. After choosing a location, the Header file
is saved as a .h file in the selected folder.
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Header file generation
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Figure 11. Header generation - save header file
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Header file generation
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3.6 Programming the device
The device can be programmed in three ways – by changing the register values directly in the GUI, by using a
Header file, which loads both Configuration and Patch files at once, or by loading the two memh files separately
using the GUI.
The Configuration and Patch files directly modify values stored in the NVM. Therefore, any changes written by
Configuration and Patch files will be retained even after reset. On the contrary, changes made by the GUI (Write
Tx button) are written into the I2C registers, which are cleared upon reset.
To load the Header file using the GUI, navigate to the Programming tab in the side menu. Select WBC86 in the
top menu and “HEADER” in the toggle selector.
Figure 12. Programming the device by header file
Select the .h file that is to be written. The GUI automatically identifies the Patch and Configuration files included in
the Header file. Press the “Write” button to load the Header file into the device.
To load the memh files (Patch and Configuration) using the GUI, navigate to the Programming tab in the side
menu. Select WBC86 in the top menu and “MEMH” in the toggle selector.
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Programming the device
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Figure 13. Generating the header file by patch and configuration files
Select Patch and Configuration files that are to be written. Press the “Write” button to load the .memh files into the
device.
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Programming the device
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4 Device description and operation
4.1 System block diagram
Figure 14. System block diagram
4.2 Integrated power inverter
The integrated power inverter is a key block in charge of converting the DC input into an AC power signal for the
transmitting coil. The power inverter consists of four N-channel MOSFET transistors arranged into a H-bridge,
conveniently driven by an internal control block, which also simultaneously monitors the key parameters of the
board to optimize switching and charging the external bootstrap capacitors for the high-side switches.
Some applications may require driving the power inverter in half-bridge mode – for example delivering a very
small amount of power might be difficult with some Tx/Rx coil combinations. The STWBC86 can be configured to
operate in half-bridge mode using the GUI.
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Device description and operation
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Figure 15. H-bridge mode settings
4.3 ADC
The STWBC86 allows the user to monitor key operational parameters using an internal ADC. Instantaneous
values can be displayed in the Charts tab of the GUI. The GUI enables the user to monitor the input voltage, input
current, device temperature, operating frequency, duty cycle, transmitted power, and more.
Figure 16. GUI charts monitoring
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ADC
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4.4 LDOs
The device is equipped with 2 internal low dropout regulators (LDOs) – a 5 V and a 1.8 V one, with the latter
deriving its power from the former.
The 1.8 V LDO powers the digital part of the IC, while the 5 V LDO powers the analog part of the IC but can also
be used to power external low-power circuitry (such as LEDs). The maximum current externally drawn from this
LDO should not exceed 10 mA.
External LDO capacitors should be placed as close to the IC as possible.
4.5 Power-up sequence
Once power is applied to the input (and the device is not forced into reset), the power-up sequence of the device
starts. After the internal main LDO reaches the target output voltage, the digital core of the device starts
operating. Default device settings are used until the digital core is woken up after which the firmware loads
settings saved in the Configuration file.
If both Patch and Configuration files are loaded into the device and the automatic start function is enabled, the
device enters the digital ping phase of power transfer (see Section 4.11 WPC Qi wireless power transfer). If the
automatic start function is disabled, the device does not proceed to the ping phase until the TX_EN command is
executed.
If Patch and/or Configuration files are not loaded, the device stays in a so-called DC mode. In this mode, the
device is powered up and ready to be programmed. The device also enters this mode if either the Patch or
Configuration, or both files, are corrupt.
4.6 UVLO
The STWBC86 is also equipped with a UVLO function. The UVLO is triggered when the input voltage drops below
2.9 V. The inverter stops switching and the device is powered down. Normal operation is resumed as soon as the
input voltage rises above 3 V.
4.7 Chip reset
The device can be forced into reset by pulling the RSTB pin to ground. This can easily be done by a jumper on
header P14. When the RSTB pin is released and allowed to be pulled up, the device resumes normal operation.
4.8 Protections overview
The STEVAL-WBC86TX board uses both hardware and software protection to ensure safe voltage and current
levels. The purpose of those protections is to avoid damage to either the board itself or even the potential
receiver, caused by unexpected conditions – overvoltage and/or overcurrent. The temperature is also monitored,
although only software protection is used for this purpose.
The software protections can be enabled/disabled in the GUI; the GUI can also be used to adjust thresholds for
the respective protections.
The hardware protections are permanently set and cannot be disabled or adjusted in the GUI. The thresholds for
the hardware protections are as follows:
• Overcurrent protection: 3 A (fuse)
• Overvoltage protection: 22 V (TVS diode)
The triggering of a software protection results in the transmitter terminating a power transfer and generating a
corresponding interrupt (can be configured in the GUI).
4.8.1 Overcurrent protection (OCP)
A transmitter overload or a short on the output (transmitting coil) may lead to excessive input current values. To
prevent damage to the transmitter caused by such currents, two separate protections (hardware and software)
are implemented.
A fuse (F1) on the input track rated at 3 A serves as the hardware protection, while an ADC monitoring the input
current serves as the software one. If the input current exceeds a set threshold, the power transmitter terminates
the power transfer and generates an OCP interrupt. The threshold is configurable in the GUI and can be set in a
range of 0 to 2500 mA.
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LDOs
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Figure 17. OCP settings
4.8.2 Overvoltage protection (OVP)
Excessive input voltage may damage the board and/or device. For this reason, a TVS diode is placed at the input
of the board. The IC is also equipped with an ADC dedicated to monitoring the input voltage level. The protection
can be enabled/disabled in the GUI and the threshold can be set in a range of 0 to 25.5 V. Triggering OVP also
leads to power transfer termination, as an increase in transmitter input voltage may also lead to an increased Rx
VRECT voltage.
Figure 18. OVP settings
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4.8.3 Overtemperature protection (OVTP)
The temperature of the IC is continuously monitored by a temperature sensor. Excessive IC temperature may
indicate that either the operating power is too high, or an internal fault occurred. It should be considered that PCB
design may affect thermal performance as well. If the temperature exceeds a set threshold, power transfer is
terminated, and an OVTP interrupt is generated by the transmitter. The threshold is configurable in the GUI and
can be set in a range of 0 to 151 °C.
Figure 19. OVTP settings
4.8.4 NTC
An external NTC can be used to further monitor the operational temperature of the board. The user may choose a
component/board region to be monitored by placing the NTC on it/nearby, although monitoring the transmitting
coil is presumably the most common practice.
Together with a pull-up resistor, the NTC forms a voltage divider, which is connected to the STWBC86 NTC pin.
The NTC pin is 1.98 V tolerant, although an internal ADC supports only up to 1.5 V NTC voltage reading.
Therefore, it is recommended to design the voltage divider to reach the (low) NTC threshold at the highest
allowed temperature, while leaving a large enough margin for accurate temperature monitoring (the NTC voltage
should be kept below 1.5 V).
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Figure 20. NTC connection on board
The user can choose if triggering this protection only generates a corresponding interrupt, or if the device also
terminates the power transfer upon triggering. The interrupt must be enabled when power transfer termination is
desired.
To set the NTC threshold using GUI, the threshold value must be set (in mV) based on the parameters of the
resistor divider. The protection will be triggered when the divider output voltage drops below the set threshold.
Figure 21. NTC settings
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