ST STEVAL-ISB68WTX User manual

Introduction
The STEVAL-ISB68WTX evaluation board based on STWLC68JRF designed for wireless power transmitter application.
STWLC68JRF can deliver up to 2.5 W power to a Qi complaint wireless receiver.
Fully integrated STWLC68JRF require few external components for board design and can work with 5-20 V input power supply.
With External USB-to-I2C bridge, the user can monitor and control the STWLC68JRF chip with the STSW-ISB68PRO Graphical
User Interface (GUI).
The STEVAL-ISB68WTX includes several safety mechanisms providing over-temperature, over-current and over-voltage
protection as well as Foreign Object Detection (FOD).
Figure 1. STEVAL-ISB68WTX
Getting started with STEVAL-ISB68WTX for 2.5W TX application
UM2901
User manual
UM2901 - Rev 1 - July 2021
For further information contact your local STMicroelectronics sales office.
www.st.com

1Board Overview
The STEVAL-ISB68WTX evaluation board default configuration is optimized for performance.
The board features:
•STWLC68JRFwireless power transmitter chip with up to 2.5 W output power capability
• Low power applications with 5 V input voltage (supplied externally or USB adapter)
• Very few external components, optimized BOM and PCB space
• On chip high efficiency full bridge inverter
• Embedded ARM Cortex™-M0+ Processor
• Wide input operating range 5 V to 20 V
• 8-channels, 10-bit A/D Converter
• On-chip thermal management and protections (over-voltage, over-current, over-temperature)
• Foreign Object Detection (FOD) supported
• 400 kHz I2C interface for communication with host system (optional)
•External USB-to-I2C converter for interfacing to STWLC68JRF chip
• On-chip thermal management and protections (over-voltage, over-current, over-temperature)
• Foreign Object Detection (FOD) supported
• 400 kHz I2C interface for communication with host system (optional)
• External USB-to-I2C converter for interfacing to STWLC68JRF chip
• Complete kit (board with embedded receiving coil, Graphical User Interface control software)
• Chip-Scale Package (CSP), ROHS Complaint
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Board Overview
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2Board configuration
The configuration settings of the STWLC68JRF chip are retrieved from the OTP memory at power-up, but they
can be temporary changed via GUI once the ISB68WTX is powered and the modified values are kept until a reset
of chip occurs.
The default STWLC68JRF settings are the following:
• The coil and resonant capacitors are designed for delivering 2.5 W using 5 V supply
• The output load to be adjusted gradually in steps of 10 mA to avoid high load transient
• The output current limit is set to 2 A
• The inverter maximum operating frequency set to 205 kHz, minimum operating frequency set to 110 kHz
• The duty cycle range minimum 20%, maximum 50%
• The ping frequency is set to 150Khz, ping interval set to 2seconds
• External TX device monitor feature is enabled
• TX Ping is disabled when external TX is detected
• TX Control Error Packet (CEP) time out set to 800msecs
• Frequency HOP frequency used in case of ASK modulation failure is set to 2900 Hz
• Control Error Packet time out max count set to 6
• Following interrupts are enabled by default
– Over Temperature Protection Interrupt (OTP)
– Over Current Protection Interrupt (OCP)
– End of Power Transfer Packet Interrupt (EPT)
– EXT TX device detect interrupt
• Switch to Qi TX Mode is disabled, need to enable it for starting TX mode
• Enable Tx ping can be used to start the ping (default it is enabled) disable TX ping
• Disable TX ping can be used to stop the Ping (power transfer will be terminated)
• Enable FOD detection (default it is disabled)
• Following Default Protection Threshold settings used
• Over Temperature Protection at 90 °C
• The default setting for the over-temperature protection consists in disabling the TX inverter output in case
one of the temperature sensors detects more than 90 °C
• Over Current Protection (OCP) at 2 A resulting in Tx Inverter output disconnection
• Over Voltage Protection (OVP) at 10 V resulting in Tx inverter output disconnection
2.1 Board configuration and test points
The STEVAL-ISB68WTX has several connectors and test points to ease access to key signals.
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Board configuration
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Figure 2. Description of test points
Figure 3. STEVAL-ISB68WTX layout
2.2 Connection to USB I2C converter board
Connect external USB converter board to P3 connector, please ensure right connections for GND, SDA, SCL
pins , as shown in below picture.
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Connection to USB I2C converter board
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Figure 4. STEVAL-ISB68WTX and USB-I2C converter
2.3 USB to I2C converter board
The USB to I2C bridging dongle is the tool that allows interfacing the receiver to the Graphical User Interface
running on a PC.
Three LEDs monitor the operation of the bridge:
D1 (green) indicates I2C bus activity.
D2 (red) indicates correct initialization of the U1 chip
D3 (yellow) is a power-on indicator.
When the dongle is plugged into the USB port, both D2 and D3 should be on.
Figure 5. USB-to-I2C converter
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USB to I2C converter board
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2.4 Board power supply
The power to the board can be supplied using 5V/2A USB adapter, connected through J1 (microUSB receptacle)
or using external 5V power source.
Ensure a stable supply using high quality cables with minimal DC resistance for best overall efficiency.
2.5 Board configuration
The configuration settings of the STWLC68JRF chip are retrieved from the OTP memory at power-up, but they
can be temporary changed via GUI once the ISB68WTX is powered and the modified values are kept until a reset
of chip occurs.
The default STWLC68JRF settings are the following:
• The coil and resonant capacitors are designed for delivering 2.5 W using 5 V supply
• The output load to be adjusted gradually in steps of 10 mA to avoid high load transient
• The output current limit is set to 2 A
• The inverter maximum operating frequency set to 205 kHz, minimum operating frequency set to 110 kHz
• The duty cycle range minimum 20%, maximum 50%
• The ping frequency is set to 150Khz, ping interval set to 2seconds
• External TX device monitor feature is enabled
• TX Ping is disabled when external TX is detected
• TX Control Error Packet (CEP) time out set to 800msecs
• Frequency HOP frequency used in case of ASK modulation failure is set to 2900 Hz
• Control Error Packet time out max count set to 6
• Following interrupts are enabled by default
– Over Temperature Protection Interrupt (OTP)
– Over Current Protection Interrupt (OCP)
– End of Power Transfer Packet Interrupt (EPT)
– EXT TX device detect interrupt
• Switch to Qi TX Mode is disabled, need to enable it for starting TX mode
• Enable Tx ping can be used to start the ping (default it is enabled) disable TX ping
• Disable TX ping can be used to stop the Ping (power transfer will be terminated)
• Enable FOD detection (default it is disabled)
• Following Default Protection Threshold settings used
• Over Temperature Protection at 90 °C
• The default setting for the over-temperature protection consists in disabling the TX inverter output in case
one of the temperature sensors detects more than 90 °C
• Over Current Protection (OCP) at 2 A resulting in Tx Inverter output disconnection
• Over Voltage Protection (OVP) at 10 V resulting in Tx inverter output disconnection
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Board power supply
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3Functional description
WPC Wireless charging system is shown in the below diagram.
The TX is responsible for controlling the transmitting coil and generating the correct amount
of power requested by the RX.
The RX continuously provides the transmitter with the correct power level requested, by modulating the
transmitter carrier through the controlled resistive or capacitive load. Generating the correct amount of power
ensures the highest level of end to-end efficiency due to reduced energy losses. It also helps maintaining a lower
operational temperature.
The TX can adapt to the amount of energy transferred by the coil by modulating the frequency, duty cycle or
amplitude of the PWM voltage on the transmitting coil.
Figure 6. Functional description
3.1 Power conversion
The power transmitter design uses a full bridge inverter to drive the primary coil and series capacitance. The
power transmitted to the coil is regulated by varying the switching frequency of bridge, higher the operating
frequency (example 200 kHz) for lower power transmission , lower operating frequency (example 110 kHz) for
Higher power transfer.
The coil used in the current design has self-inductance of 6.8 uH, the value of series capacitor 347 nF. The input
voltage to the Full bridge inverter is 5 V.
The LC resonant circuit optimization to be done based on power transfer requirements.
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Functional description
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Figure 7. Power conversation
3.2 Communication and control
The 32-bit core MCU is the supervisor of the whole device and manages all the functional blocks to establish and
maintain communication with the receiver.
Ensure adherence to Qi standard specifications (wherever required), optimize the efficiency by properly adjusting
the operating point and guarantee reliability by monitoring and protecting the device.
3.3 ASK demodulation
Using ASK modulation, the receiver sent Control Error Packets (CEP) to tune operating point for matching load
requirements, the transmitter coil signals are filtered using demodulation filter circuit as shown below and feed in
to VS pin of STWLC68JRF.
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Communication and control
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Figure 8. ASK demodulation circuit
3.4 FOD
STWLC68JRF has FOD detection feature. Any excess power loss in wireless power transfer can be monitored
and the device can stop power transfer.
The FOD detection is enabled by setting TX_FOD_EN bit to 1 in register 0x0021h.
The AUTO FOD detection threshold can be set in AUTO_FOD_THR register 0x00EBh.
FOD is detected when abs(PTX-PRX) > TX_AUTO_FOD_THR * 20mW (20mW unit).
PTX is TX power transferred to RX : Monitor register 0x0070h (2bytes)
PRX is TX Power received by RX : Monitor register 0x0072h (2bytes).
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FOD
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4Component Layout
Figure 9. Component layout
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Component Layout
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