ST STDES-WLC38WA Instructions for use

Introduction
The STDES-WLC38WA reference design, based on STWLC38, is designed for wireless power receiver applications. It allows
the user to start a 2.5 W wireless charging project quickly.
It features a small size, good thermal performance, and stable power transfer.
The integrated circuit requires only few external components. The device output voltage is adjustable (the default value is 5 V).
Through an external USB-to-I²C converter, you can monitor and control the STWLC38 using the STSW-WPSTUDIO GUI.
The STDES-WLC38WA includes several safety mechanisms that provide overtemperature (OTP), overcurrent (OCP), and
overvoltage (OVP) protections, which can protect the device by sending an end power transfer (EPT) packet, disable the device
output, or short the receiving coil.
Figure 1. STDES-WLC38WA reference design
Fully assembled board developed for
performance evaluation only,
not available for sale
The STDES-WLC38WA reference design is ready to use with the STDES-WBC86WTX.
Figure 2. STDES-WLC38WA reference design plus STDES-WBC86WTX
Fully assembled board developed for
performance evaluation only,
not available for sale
Install the I²C drivers and the STSW-WPSTUDIO GUI.
STDES-WLC38WA wireless power receiver quick start guide and test report
TN1440
Technical note
TN1440 - Rev 2 - August 2023
For further information contact your local STMicroelectronics sales office.
www.st.com

Using an external USB-to-I²C bridge, connect the board to your PC (connector P2 on the USB-I²C bridge). This allows you to
communicate with the board, program it, and monitor its functions.
Figure 3. STDES-WLC38WA reference design plus USB-to-I²C bridge
Fully assembled board developed for
performance evaluation only,
not available for sale
The GUI supports MCP2221 and FT260Q-T USB-I²C converters. Standard connections are described in the datasheets of the
converters.
TN1440
TN1440 - Rev 2 page 2/19

1 Overview
The STDES-WLC38WA is optimized for performance. The board and IC feature:
• High efficiency (98% typical) synchronous rectifier operating up to 800 kHz
• Low drop-out linear regulator with output current limit and input voltage control loop
• Adaptive rectifier configuration (ARC) mode for enhanced spatial freedom
• 4 V to 12 V programmable output voltage
• 32-bit, 64 MHz Arm® Cortex® M0+ core with 32kB RRAM, 16 KB SRAM, 64kB ROM
• 10-bit A/D converter
• Configurable GPIOs
• I²C slave interface
• Multilevel ASK modulator, enhanced FSK demodulator
• Output overvoltage clamping protection
• Accurate voltage/current measurement for foreign object detection (FOD)
• On-chip thermal management and protections
• Flip chip 40 bumps (2.12 mm x 3.32 mm) package
• Small, ready to use 20 mm board
• I²C connector, GPIO, and INT connector, SOVP resistor
Figure 4. STDES-WLC38WA connection overview
The STDES-WLC38WA is equipped with all components necessary for a standalone operation. The coil has to be
connected to pads (COIL1 and COIL2). The pad labeled as AC1 is used for debug purposes.
The rectifier output is labeled VRECT. The output voltage is VOUT. The I²C interface is used to monitor/control the
device. GPIOs are accessible on the six-pin header.
1.1 Test points
STDES-WLC38WA features several connectors and test points to provide easy access to key signals.
Table 1. Connectors and test points
Connector/test point Name Description
Connector P1 Coil connection and AC1 debug output
Connector P2 GPIO and INT connector
Connector P3 VRECT and VOUT connector
Connector P4 I²C connector
Test point VAA Test point of internal LDO
Test point VDD Test point of internal LDO
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Overview
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2 Reference design specifications
Target specification of the STDES-WLC38WA reference design are listed in the table below.
Table 2. STDES-WLC38WA specifications
Parameter Description
RX application PCB area 20 mm
RX coil specifications Inductance 11.8 µH, dimensions Φ15 mm
Output voltage (VOUT)5 V
Output current (IOUT)0.5 A
Host MCU STM32 used as a reference, the reference I²C driver can be ported to any other
MCU family
Efficiency
58.24% (2.5 W operation)with STDES-WBC86WTX
60.23% (peak efficiency)with STDES- WBC86WTX at 2 W
Total distance between coils 3mm.
Applicable charging gap between Tx
and Rx coils (z-distance)
4 mm (X and Z axis; 2.5 W output) with the STDES- WBC86WTX transmitter,
maximum 7 mm – stable communication without output enabled
Operational modes Receiver only
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Reference design specifications
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3 Default configuration
Table 3. Basic parameters
RX rectifier mode Full sync
Minimum operating frequency 110 kHz
Maximum operating frequency 205 kHz
Overcurrent protection (OCP – FW/HW) 1.85 A/1.93
Overvoltage protection (OVP – FW/HW) VOUT +4 V/16 V
Overtemperature protection (OVTP – FW/HW) 85°C/105°C
Default output voltage 5 V
• Enabled interrupts
– OCP triggered
– OVP triggered
– OVTP triggered
– UVLO triggered
– OUTPUT enabled
– Message received
• GPIOs
– GPIO3 – Interrupt pin
• Protections enabled
– ADC OCP
◦ Send EPT
◦ Disable VOUT
– ADC OVTP
◦ Send EPT
◦ Disable VOUT
– SOVP
◦ Connect IEXT resistor between Vrect and ground
– TSHUT (HW OVTP)
◦ Disable VOUT
◦ Short RX COIL
– HOVP (HW OVP)
◦ Short RX COIL
– OCP (HW)
◦ Disable VOUT
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Default configuration
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4 PCB layout
Figure 5. STDES-WLC38WA top layer
Figure 6. STDES-WLC38WA inner1 layer
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PCB layout
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Figure 7. STDES-WLC38WA inner2 layer
Figure 8. STDES-WLC38WA bottom layer
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PCB layout
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5 Typical performance characteristics
The following table shows charging performance of the STDES-WBC86WTX/STDES-WLC38WA (Tx/Rx) setup at
various load currents, with the temperature being measured after 5 minutes of continuous operation.
Table 4. Typical performance characteristics
Vin [V] Iin [mA] Pin [mW] Vout [V] Iout [mA] Pout [mW] Eff [%] TX Trect [°C] RX Trect [°C]
5.09 263 1338.67 5.035 100 503.5 37.61 42 37
5.042 382 1926.04 5.032 200 1006.4 52.25 45.5 39
5.026 502 2523.052 5.032 300 1509.6 59.83 49.8 44
4.986 670 3340.62 5.03 400 2012 60.23 58.2 49
4.985 860 4287.1 5.028 500 2514 58.64 65.2 57
5.1 Efficiency and spatial freedom in the XY plane
Efficiency is one of the most important metrics of wireless charging performance evaluation. Another important
metric is the spatial freedom, that is the size of the area in which a power receiver can be placed on the power
transmitter, which still allows sufficient power to be transmitted.
The STDES-WLC38WA efficiency and spatial freedom have been measured with the STDES-WBC86WTX as the
receiver. The efficiency has been measured from the transmitter DC input to the receiver DC output. The
measurement does not include any power losses in the input cable from the power supply.
The test setup consists of:
• a power supply (HMP4040)
• a transmitter (STDES-WBC86WTX)
• a receiver (STDES-WLC38WA)
• an electronic load in CC mode (model BK Precision 8500)
The maximum efficiency achieved with this setup was 60.23% at a 2 W (5 V/400 mA) load. The total gap between
the Rx and Tx coils was 3 mm.
Note: This efficiency measurement has been performed with a Φ15 mm small Rx coil and a Φ20mm Tx coil.
Figure 9. STDES-WLC38WA and STDES-WBC86WTX efficiency test
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Typical performance characteristics
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5.2 Thermal performance
The following picture shows the STDES-WLC38WA thermal performance with a 2.5 W load (5 V/0.5 A on the Rx
side) after 10 minutes of continuous operation.
The temperature measured by the thermal-imaging camera can be different from the value measured by TRECT,
as the TRECT temperature is measured inside the device.
Figure 10. STDES-WLC38WA thermal performance (1 of 2)
Figure 11. STDES-WLC38WA thermal performance (2 of 2)
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Thermal performance
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5.3 Startup waveform
A start-up waveform of STDES-WLC38WA and STDES-WBC86WTX is shown below.
The start-up conditions are center position of RX and TX coil, 3mm gap between coil and 100mA load on Rx Vout.
The STDES-WBC86WTX is powered from a 5 V power supply.
Figure 12. STDES-WLC38WA startup waveform
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Startup waveform
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