ST STDES-50W2CWBC Fiche technique

Introduction

The STDES-50W2CWBC dual-coil reference design is based on the STWBC2-HP Qi-compliant, inductive wireless charger

transmitter. It supports two coils, which could work alternatively to increase the Rx positioning freedom. The solution supports

Qi EPP-compliant mode up to 15 W, featuring an ST proprietary protocol. It can also support 50 W or an even higher wireless

power transfer.

The embedded STWBC2-HP integrates the following main components:

• three pairs of half-bridge gate drivers

• a dedicated DC-DC controller that supports buck, boost, and buck-boost topologies

• high-performance Q-factor detection hardware

• a high-resolution main PWM controller

• a dedicated Qi communication modulator and demodulator

• a USB-PD controller

• a buck DC-DC

• a charge-pump

The STDES-50W2CWBC is a fully assembled reference design developed for performance evaluation only, not available for

sale.

To achieve the best performance, carry out some procedures before finalizing the application.

This document summarizes the following fundamental steps:

• power supply test

• firmware downloading test

• power-on LED status check

• parameter setting test

• presence detection test

• power transfer switching test

• ST super charger (STSC) protocol test

• ASK demodulation test

• Q-factor accuracy test

STDES-50W2CWBC test report

TN1399

Technical note

TN1399 - Rev 1 - March 2022

For further information contact your local STMicroelectronics sales office.

www.st.com

1Overview

Wireless power transfer is a fast-growing technology in many application fields. The wireless power can be from

several mW (for example, in the medical field) to tens of kW (for example, an electronic vehicle).

There are multiple physical mechanisms to address the wireless power, such as magnetic inductance, magnetic

resonance, capacitive coupling, radio frequency, laser charging, etc.

The most popular mechanism is the magnetic inductive that follows the Qi standard defined by the Wireless

Power Consortium (WPC).

The STDES-50W2CWBC dual-coil reference design follows the WPC MP-A2 topology.

Figure 1. STDES-50W2CWBC reference design

Fully assembled board developed for

performance evaluation only,

not available for sale

Figure 2. Block diagram of a typical power transfer system

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Overview

TN1399 - Rev 1 page 2/26

2Specifications

The STDES-50W2CWBC specifications can be summarized as follows (refer to the figure below for the related

blocks):

• the boost DC-DC supports 60 W (20 V/3 A) input and 30 V+ output

• the full bridge converter supports an AC voltage ≤ ±100 V

• the coil switcher alternatively switches the two LC tanks for coils alternatively into high voltage

• the STLINK-V3MINI interface with SWD for firmware debug and UART for demo GUI

• the I²C interface supports external daughter boards through I²C (for example, STSAFE-A110 for

authentication)

Figure 3. STDES-50W2CWBC main blocks

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Specifications

TN1399 - Rev 1 page 3/26

3Test setup

3.1 Test conditions and equipment

The following tables list the equipment and tools used to test the STDES-50W2CWBC.

Table 1. Test equipment

Item Type Features/Description Reference

I1 STDES-50W2CWBC Evaluation board x1

I2 34401A 6 ½ digit multimeter by Agilent x1

I3 6403E PC oscilloscope by Pico x1

I4 E4980A LCR meter by Keysight x1

Table 2. Test tools

Item Type Description Order code/Reference Provided by

C1 STLINK-V3MINI STLINK-V3 compact in-circuit debugger and

programmer for STM32 STLINK-V3MINI Yes

C2 STM32Cube STM32 programmer tool used to download

the firmware into the evaluation board STM32Cube Yes

C3 STWBC2 GUI Tool to check the board behavior, perform

the tuning, and collect logs in case of failure - Yes

C4 Firmware Firmware binary stdes-50w2cwbc_FW_v1.0.0.0.hex Yes

C5 STWLC88 or

STWLC98

Qi-compliant inductive wireless charger

power receiver for 50 W applications or 70

W applications

STWLC88 or STWLC98 Yes

C6 Wall adapter USB PD wall adapter - No

C7 USB Type-C™ cable 4 A or 5 A cable - No

3.2 Procedure

To achieve the best performance, follow the procedure below.

Step 1. Test the power supply.

The on-board DC-DC buck converter provides a supply voltage VDD starting from an external VIN DC

source. The VDD voltage is available on an external pin. It supplies the internal voltage regulators LDO

3V3 and LDO 1V8. These regulator outputs are available on an external pin. The STWBC2-HP should

generate its own power supplies directly from the VIN.

The aim of this test is to ensure that the STWBC2-HP is correctly powered. The table below shows the

reference range.

Table 3. Internal voltage range

Item Min. (V) Typ. (V) Max. (V)

VBUCK 3.42 3.6 3.78

LDO 3V3 3.1 3.3 3.5

LDO 1V8 1.7 1.8 1.9

Step 2. Download the firmware.

The firmware offers all the standard functionalities. It also supports the STWBC2-HP embedded USB-

PD.

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Test setup

TN1399 - Rev 1 page 4/26

Step 3. Check the status of the power-on LEDs to ensure that the STWBC2-HP is correctly working.

There are three LEDs on the board that indicate the STWBC2-HP power-on status when the firmware

is available.

The table below shows the correct LED status.

Table 4. Power-on LED status

Item Color Behavior

D209 Green Always on

D202 Red Long blink once plus short blink once

D203 Green Long blink once

Step 4. Set the STWBC2-HP parameters for the board initialization.

Important: Disable the FOD and protection features in the STWBC2_GUI.

Step 5. Test the presence detection alternatively on the two coils.

The table below shows the level, duration, and cycle of the presence detection.

Table 5. Presence detection specifications

Item Level (V) Duration (ms) Cycle (ms)

RING_NODE1 ~6 ~80 ~1900

RING_NODE2 ~6 ~80 ~1900

Step 6. Test the power transfer switching.

The oscillation waveform appears in the activated RING_NODE, while the switching waveform appears

in another inactive RING_NODE. The switching waveform should be off in the half bridge mode and

square-waved in the full bridge mode.

Step 7. Test the ST super charger (STSC) protocol.

The STSC can support a higher power transfer than the Qi EPP. The table below shows its basic

behavior.

Table 6. Level of the STSC power supplies

Mode VIN VDCDC

Presence detection 5 V 12 V

Digital ping 9 V 12 V

STSC 5 V 9 V 12 V

STSC 9 V 9 V 9 V

STSC 12 V 12 V 12 V

STSC 15 V 15 V 15 V

STSC 18 V 15 V 16.5~18 V

STSC 20 V 20 V 20 V

Step 8. Test the ASK demodulation.

The firmware can route the demodulation result (V, I) to a GPIO, which should be close to the Rx

modulation waveform.

Step 9. Test the Q-factor accuracy.

Comparing the Q-factor measurement accuracy with the LCR meter, the Q-factor measurement

accuracy should be close to the LCR meter.

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Procedure

TN1399 - Rev 1 page 5/26

4Measurements/waveforms/test data

4.1 STWBC2-HP startup waveform

Once the board is supplied, you can check each voltage during the startup as described below:

1. the board is supplied by the USB PD adapter and the voltage is ready and stable at about 5 V

2. the internal DC-DC buck converter and LDOs are starting

3. the internal 1.8 V LDO is ready and the output is stable at 1.8 V

4. the internal 3.3V LDO is ready and the output is stable at 3.3 V

5. the internal DC-DC buck converter is ready and the output is stable at 3.6 V

Figure 4. Typical startup waveform: power-on sequence

4.2 Presence detection waveform

Once the STWBC2-HP power-up is ready, you can check the presence detection waveform at RING_NODE1

triggered by TANK1_SEL and RING_NODE2 triggered by TANK2_SEL as described below:

1. the RING_NODE1 starts oscillating about 75 ms in the end of TANK1_SEL active high and the

RING_NODE2 is off

2. the RING_NODE2 starts oscillating about 75ms in the end of TANK2_SEL active high and the

RING_NODE1 is off

3. the RING_NODE1 starts oscillating again in the end of TANK1_SEL active high and the RING_NODE2 is off

4. the RING_NODE1 and RING_NODE2 repeat the above process in a period of about 900 ms

TN1399

Measurements/waveforms/test data

TN1399 - Rev 1 page 6/26

Figure 5. Presence detection waveform

4.3 Power transfer switching waveform

Once the STWBC2-HP presence detection is working correctly, you can check the power transfer switching

waveform at RING_NODE1 reference to TANK1_SEL and RING_NODE2 reference to TANK2_SEL as described

below.

1. Put the Rx coil on the Tx coil 1 and set the Rx output to 5 V. The RING_NODE1 appears sine-waved while

the RING_NODE2 is off (see Figure 6).

2. Put the Rx coil on Tx coil 2 and set the Rx output to 5 V. The RING_NODE2 appears sine-waved while the

RING_NODE1 is off (see Figure 7).

3. Put the Rx coil on the Tx coil 1 and set the Rx output to 9 V. The RING_NODE1 appears sine plus

square-waved while the RING_NODE2 is square-waved (see Figure 8).

4. Put the Rx coil on the Tx coil 2 and set the Rx output to 5 V. The RING_NODE2 appears sine plus

square-waved while the RING_NODE1 is square-waved (see Figure 9).

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Power transfer switching waveform

TN1399 - Rev 1 page 7/26

Figure 6. Coil 1 in half-bridge mode

Figure 7. Coil 2 in half-bridge mode

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Power transfer switching waveform

TN1399 - Rev 1 page 8/26

Figure 8. Coil 1 in full-bridge mode

Figure 9. Coil 2 in full-bridge mode

4.4 STSC waveform

The STSC protocol supports a higher power transfer. The figure below shows the typical waveform.

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STSC waveform

TN1399 - Rev 1 page 9/26

Figure 10. Power automatic boost (5-20 V)

4.5 ASK demodulation waveform

The firmware can route the demodulation result (V, I) to a GPIO, which should be close to the Rx modulation

waveform. The figure below shows the typical waveform.

Figure 11. ASK demodulation frame

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ASK demodulation waveform

TN1399 - Rev 1 page 10/26

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