STDES-WLC38TWS Wireless Power Receiver User Manual

STDES-WLC38TWS Wireless Power Receiver

Product Information

STDES-WLC38TWS Wireless Power Receiver

The STDES-WLC38TWS is a reference design for wireless power receivers. It is optimized for performance and features a small size, good thermal performance up to 2.5 W, and stable power transfer with standard Qi wireless chargers.

The key features of the STDES-WLC38TWS reference design include:

• 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
• 10-bit A/D converter
• Configurable GPIOs
• 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

Connection Overview

The STDES-WLC38TWS is equipped with all components necessary for standalone operation. The TWS coil needs to be connected to pads (COIL1 and COIL2), and the AC1 is the debug output. GPIOs are alsoavailable on the header.

Reference Design Specifications

Applicable charging gap between Tx and Rx coils
(z-distance)| 3 mm
Operational modes| Receiver only

Product Usage Instructions

Connection

To use the STDES-WLC38TWS, follow these steps for connection:

1. Connect the TWS coil to the COIL1 and COIL2 pads.
2. Connect the AC1 debug output.
3. Use the available GPIOs on the header if needed.

Test Points

The STDES-WLC38TWS features several connectors and test points for easy access to key signals. The connectors and test points are as follows:

Default Configuration

The default configuration of the STDES-WLC38TWS includes the following:

• Enabled interrupts
• GPIOs
• Protections enabled
• Send EPT
• Disable VOUT
• Connect IEXT resistor from Vrect through IEXT resistor, internal transistor to Ground
• Short RX COIL
• Disable VOUT

PCB Layout

The STDES-WLC38TWS has a 3-layer PCB layout. The top, inner1, inner2, and bottom layers of the PCB are shown below:

Introduction

• The STDES-WLC38TWS 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.
• The integrated circuit requires only few external components. It can work with adjustable output voltage (the default output voltage is 5 V).
• Through an external USB-to-I²C converter, you can monitor and control the STWLC38 using the STSW-WPSTUDIO GUI. The STDES-WLC38TWS 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 coil inputs.

The STDES-WLC38TWS reference design is ready to use. It features a small size, good thermal performance up to 2.5 W, and stable power transfer with standard Qi wireless chargers. Install the I²C drivers and the STSW-WPSTUDIO GUI. 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. The GUI supports MCP2221 and FT260Q-T USB-I²C converters with the standard connections described in the datasheet of the USB-I²C bridge.

Overview

The STDES-WLC38TWS 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

The STDES-WLC38TWS is equipped with all components necessary for a standalone operation. The TWS coil has to be connected to pads (COIL1 and COIL2). The AC1 is the debug output. The rectifier output is labeled VRECT. The output from the main regulator is VOUT. The I²C interface is led by connector SDA, SCL and GND for connection to the I²C bus USB-I²C bridge. GPIOs are available on the header as well. The board includes capacitors for VRECT and VOUT, CTANK capacitors calulated with the TWS coil, SOVP resistor, and other necessary components.

Test points
STDES-WLC38TWS features several connectors and test points to provide easy access to key signals.

Table 1. Connectors and test points

Reference design specifications

The STDES-WLC38TWS target specifications are listed in the table below.
Table 2. Reference design specifications

any other MCU family

Efficiency

| 67 % (2.5 W operation) with the STEVAL- WBC86TX

Total distance between coils 3 mm

Applicable charging gap between Tx and Rx coils

(z-distance)

| 8 mm (X; 2.5 W output) with STEVAL-WBC86TX transmitter, maximum 14 mm – stable communication without output enabled 10 mm (Z; 2.5 W output) with STDES- WBC86WTX transmitter, maximum 15 mm – stable communication without output enabled
Operational modes| Receiver only

Default configuration

Basic parameters:

Table 3. Basic parameters

• 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 from Vrect through IEXT resistor, internal transistor to Ground
  • TSHUT (HW OVTP)
  • Disable VOUT
  • Short RX COIL
  • HOVP (HW OVP)
  • Short RX COIL
  • OCP (HW)
  • Disable VOUT
  • TN1441
  • Default configuration
  • TN1441

PCB layout

Typical performance characteristics

The following table shows charging performance of the STEVAL-WBC86TX/STDES- WLC38TWS (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]
---|---|---|---|---|---|---|---|---
5.03| 200| 1006| 5| 100| 500| 49.70| 30.2| 37
5.01| 322| 1613.22| 5| 200| 1000| 61.99| 30.3| 41
5| 453| 2265| 5| 300| 1500| 66.23| 32| 45
4.989| 598| 2983.422| 5| 400| 2000| 67.04| 33.9| 50
4.97| 750| 3727.5| 5| 500| 2500| 67.07| 36.2| 56
4.96| 913| 4528.48| 5| 600| 3000| 66.25| 36.9| 63
4.95| 1075| 5321.25| 4.99| 700| 3493| 65.64| 40.2| 67
4.94| 1249| 6170.06| 4.989| 800| 3991.2| 64.69| 43.7| 72
4.93| 1423| 7015.39| 4.987| 900| 4488.3| 63.98| 47.3| 77
4.91| 1602| 7865.82| 4.984| 1000| 4984| 63.36| 51.6| 81

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- WLC38TWS efficiency and spatial freedom have been measured with the STEVAL- WBC86TX as the receiver. The efficiency has been measured from the transmitter DC input to the receiver DC output. Themeasurement 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 (STEVAL-WBC86TX)
• a receiver (STDES-WLC38TWS)
• an electronic load in CC mode (model BK Precision 8500)

The maximum efficiency achieved with this setup was 67% at a 2.5 W (5 V/500 mA) load. The total gap between the Rx and Tx coils was 3 mm.
Efficiency curves for various misalignments in the X and Y axis are shown in the figure below. Efficiency and spatial freedom in the Z-axis
The Z-axis distance between the coils, also known as the charging gap, is an additional parameter, which significantly affects the charging performance. Therefore, the STDES-WLC38TWS has also been tested atvarious charging gap distances.
Efficiency curves for misalignment in the Z-axis are shown in the figure below .

A Z-distance of 3 mm is a typical value for most applications (2 mm on the Tx side + 1 mm on the Rx side). The transmitter can deliver sufficient power even with a 5 mm charging gap. However, the efficiency rapidly decreases proportionally to the increasing charging gap. Therefore, minimizing the Z-distance whenever possibleis recommended.

Thermal performance
The following picture shows the STDES-WLC38TWS 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.

Startup waveform
A startup waveform of STDES-WLC38TWS and STEVAL-WBC86TX is shown below. The startup conditions are center position of Rx and Tx coil, 3 mm gap between coil and 100 mA load on Rx Vout.The STEVAL-WBC86TX is powered from a 5 V power supply.

Schematic diagrams

Bill of materials

Table 5. STDES-WLC38TWS bill of materials

Item| Q.ty| Ref.| Value| Description| Manufacturer| Order code
---|---|---|---|---|---|---

1

| ****

1

| ****

C1

| 4.7uF, C0402,

6.3 V

| 4.7uF, 6.3V,

±10%, X5R,

0402

| Wurth Elektronik| ****

885012105008

2

| ****

1

| ****

C2

| 1uF, C0402, 6.3 V| 1µF, 6.3V,

±10%, X7R,

0402

| Wurth Elektronik| ****

885012105006

3

| ****

2

| ****

CBT1, CBT2

| 47n, C0402, 25 V| 47nF, 25V,

±10%, X7R,

0402

| Wurth Elektronik| ****

885012205054

4

| ****

2

| ****

CMA1, CMA2

| 22n, C0402, 25 V| 22nF, 25V,

±10%, X7R,

0402

| Wurth Elektronik| ****

885012205052

5

| ****

2

| ****

CMB1, CMB2

| 10n, C0402, 25 V| 10 ㎋, 25V,

±10%, X7R,

0402

| Wurth Elektronik| ****

885012205050

6

| ****

4

| CO1, CO2, CR1, CR2| 10uF, C0805,

25 V

| 10uF, 25V,

±10%, X5R,

0805

| ****

Murata

| ****

GRM21BR61E106KA73L

7| 1| CPAR| 1nF, C0402, 25 V,| 1nF, 25V, ±10%,

X7R, 0402

| Wurth Elektronik| 885012205044

8

| ****

3

| ****

CS1, CS2, CS3

| 100n, C0402,

25 V

| 100 ㎋, 25V,

±10%, X7R,

0402

| Wurth Elektronik| ****

885012205085R

9| 1| CS4| N.M., C0402| N.M.| –| –
10| 1| LED1| RED/1005, LED1005, 1.8 V| RED, 2mA, 1.8V, 0402| Kingbright| APHHS1005LSECK/J3-PF
11| 1| NTC| 100K, R0402| 100Kohm, ±1%| Murata| NCP15WF104F03RC

12

| ****

1

| ****

P1

| HEADER2X2_P 2.54, HEADER2X2_P 2.54| 13uH, T=0.6mm,

solder on pin 2 and 4 (edge of PCB)

| ****

Luxshare

| ****

LE15FP005-1H

13

| ****

1

| ****

P2

| N.M., HEADER3X2_P 2.54|  | ****

Samtec

| ****

TSW-103-23-F-D

14

| ****

2

| ****

P3, P4

| N.M., HEADER3X1_P 2.54|  | ****

Harwin

| ****

M20-9990345

15| 3| R1, R2, R3| 100K, R0201|  | YAGEO| RC0201FR-07100KL
16| 1| R4| 750R, R0201|  | YAGEO| RC0201FR-07750RL

17

| ****

1

| ****

REXT1

| 100R, R0805,

500 mW, 0,05

%

| ****

100Ω, 0805

| ****

Panasonic

| ****

ERJ-P06J101V

18

| ****

1

| ****

U1

| ****

STWLC38JRM, WLCSP40 2.126X3.327X0.

546 0.4P 0

| Qi-compliant inductive wireless power receiver for up to 15W applications|

ST

| ****

STWLC38JRM

19| 2| VAA, VDD| TP1.0, TP1.0| Test points N.M.| –| –
Item| Q.ty| Ref.| Value| Description| Manufacturer| Order code
---|---|---|---|---|---|---
20| 1| –| –| Plastic spacer| Any| Any
21| 1| –| 2 mm| Adhesive tape| Any| Any

Conclusions

The test results show that the STDES-WLC38TWS reference design can automatically detect TX and able to receive requested power from the STEVAL- WBC86TX transmitter board. The peak efficiency of STEVAL-WBC86TX and STDES- WLC38TWS is > 67 % at 2.5 W. The STDES-WLC38TWS reference design achieved expected performance with the STEVAL-WBC86TX transmitter board.

Appendix

Appendix A Reference design warnings, restrictions and disclaimer

Important: The reference design is not a complete product. It is intended exclusively for evaluation in laboratory/ development environments by technically qualified electronics experts who are familiar with the dangers andapplication risks associated with handling electrical/mechanical components, systems and subsystems.

Danger: Exceeding the specified reference design ratings (including but not limited to input and output voltage, current, power, and environmental ranges) may cause property damage, personal injury or death. If there are questions concerning these ratings, contact an STMicroelectronics field representative prior to connecting interface electronics, including input power and intended loads. Any loads applied outside of the specified output range may result in unintended and/or inaccurate operation and/or possible permanent damage to the reference design and/or interface electronics. During normal operation, some circuit components may reach very high temperatures. These components include but are not limited to linear regulators, switching transistors, pass transistors, and current senseresistors which can be identified in the reference design schematic diagrams.

STMicroelectronics reference designs are solely intended to assist designers (“buyers”) who are developing systems that incorporate STMicroelectronics semiconductor products (herein, also referred to as “components”). The buyer understands and agrees that he/she is the only responsible for independent analysis, evaluation and judgment in designing his/her own systems and products. STMicroelectronics has conducted only the measurements and tests specifically described in the published documentation for the specified reference design. STMicroelectronics may correct, enhance, improve its reference designs for future development. STMicroelectronics reference designs are provided “as is”. STMicroelectronics does not promise that reference designs are accurate or error free. STMicroelectronics makes no warranties or representations with regard to the reference designs or use of the reference designs, express, implied or statutory, and specifically disclaims all warranties, express or implied, as to the accuracy or completeness of the information contained therein. STMicroelectronics disclaims any warranty of title and any implied warranties of merchantability, fitness for a particular purpose and non-infringement of any third-party intellectual property rights concerning STMicroelectronics reference designs or their use. STMicroelectronics shall not be liable for and shall not defend or indemnify buyers against third-party infringement claim that relates to or is based on a combination ofcomponents provided in an STMicroelectronics reference design.In no event shall STMicroelectronics be liable for any actual, special, incidental, consequential or indirect damages, however caused, on any theory of liability and whether or not STMicroelectronics has been advised of  the possibility of such damages, arising in any way out of STMicroelectronics reference designs or buyer’s use of STMicroelectronics reference designs. You further acknowledge and agree that the reference designs may not be used in or in connection with any legal or administrative proceeding in any court, arbitration, agency, commission or other tribunal or in connection with any action, cause of action, litigation, claim, allegation, demand or dispute of any kind.

Revision history
Table 6. Document revision history

01-Aug-2023

| ****

2

| Modified title in cover page.

Updated Section 6 Schematic diagrams and Section 7 Bill of materials.

List of tables

• Table 1. Connectors and test points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
• Table 2. Reference design specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
• Table 3. Basic parameters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
• Table 4. Typical performance characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
• Table 5. STDES-WLC38TWS bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
• Table 6. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

List of figures

• Figure 1. STDES-WLC38TWS reference design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
• Figure 2. STDES-WLC38TWS connection overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
• Figure 3. STDES-WLC38TWS top layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
• Figure 4. STDES-WLC38TWS inner1 layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
• Figure 5. STDES-WLC38TWS inner2 layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
• Figure 6. STDES-WLC38TWS bottom layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
• Figure 7. STDES-WLC38TWS and STEVAL-WBC86TX efficiency test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
• Figure 8. STDES-WLC38TWS and STEVAL-WBC86TX efficiency test in the Z-axis . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
• Figure 9. STDES-WLC38TWS thermal performance (1 of 2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
• Figure 10. STDES-WLC38TWS thermal performance (2 of 2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
• Figure 11. STDES-WLC38TWS startup waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
• Figure 12. STDES-WLC38TWS startup waveform with ARC mode and Z gap 14mm . . . . . . . . . . . . . . . . . . . . . . . . . . 11
• Figure 13. STDES-WLC38TWS circuit schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

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References

• STDES-WLC38TWS - Qi-1.3 compatible wireless power receiver reference design for 2.5W True Wireless Stereo (TWS) applications - STMicroelectronics
• STEVAL-WBC86TX - Qi-compatible wireless power transmitter evaluation board for 5 W application based on STWBC86 - STMicroelectronics
• STSW-WPSTUDIO - Graphical user interface for wireless power receiver and transmitter evaluation boards - STMicroelectronics
• STWLC38 - Qi-compliant inductive wireless charger power receiver for up to 15W applications - STMicroelectronics

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