Getting started with STEVAL-ISB68WA wireless power

IntroductionThe STEVAL-ISB68WA is an evaluation kit based on STWLC68JRH wireless power receiver and it is designed as referencesolution for wearable applications. The kit consists of a wireless receiver module and USB-to-I2C bridging dongle. The receiveris a 3-elements stack: a PCB housing the STWLC68JRH wireless power receiver and all the required external components, a 2mm thick plastic spacer and a 15 mm diameter receiving coil facing the bottom side.

Figure 1. Receiver module

The module is configured to provide a constant 5 V output voltage with a maximum power capability of 2.5 W and it works out ofthe box when placed on a suitable wireless power transmitter.An on-board LED indicates when the communication with thetransmitter succeeds and the power transfer is in progress.Thanks to the I2C interface, the module can be easily controlled andconfigured through the dedicated Graphical User Interface (GUI) by using the enclosed USB-to-I2C dongle.

The complete reference application is confined in a 10x10 mm area of the PCB and all the components are intentionally spacedto ease probing and customization to the end user.

Getting started with STEVAL-ISB68WA wireless power receiver evaluation kit for wearable applications

UM2693

User manual

UM2693 - Rev 1 - February 2020For further information contact your local STMicroelectronics sales office.

www.st.com

1 Wireless power receiver module

OverviewAs visible in Figure 2, the schematic diagram of the wireless power receiver is relatively simple. The RX coil (J1-J2 terminal) is part of the series resonant circuit (C1 through C4 capacitors) that provides the AC voltage to theAC1-AC2 pins of the STWLC68JRH. The rectified voltage is filtered by C15 through C17 capacitors andaccessible at J3 connector, mainly used to monitor the ping-up behavior and the ASK modulation. The output rail(VOUT pins) is filtered by C18 through C20 capacitors and made available at J5 terminal. Few additionalcomponents are needed to complete the wireless receiver: bootstrap capacitors for the rectifier (C8 & C11) andfor the main linear regulator (C12), modulation capacitors (C6, C7, C9 and C10) and filtering capacitors for the 1.8V and 5 V supply rails (C13 & C14). The R1 resistor is connected between VRECT and IEXT to implement anactive clamper to prevent excessive voltages (Over-Voltage Protection). Transient voltage Suppressors (D1 & D2)are recommended to protect the application against ESD.

Figure 2. Receiver module schematic

UM2693Wireless power receiver module

UM2693 - Rev 1 page 2/18

The terminals for the receiving coil, the output load and the control signals are summarized in Table 1. The outputrail and the control interface are already made easily accessible by means of wires terminated with pin headerfemale connectors (Figure 4).

Table 1. Receiver module terminals

Terminal Signal Wiring color

J1 AC input (RX coil) -

J2 AC input (RX coil) -

J3 VRECT (rectifier output) -

J4 Power return (ground) Black (P1)

J5 VOUT power output Red (P1)

J6 INT (digital output) Orange (P2)

J7 SCL (digital input) Yellow (P2)

J8 SDA (digital I/O) Green (P2)

J9 Signal ground Blue (P2)

Figure 3. Receiver module top and bottom silkscreen


UM2693 - Rev 1 page 3/18

Figure 4. Receiver module wiring

Additional control signals and programmable general-purpose I/O pins are available at the STWLC68JRH, butthey are not used in the module to keep the reference solution as simple as possible. The STWLC68JRH chip canhandle up to 400 kHz speed over the I2C bus. Table 2 summarizes the default STWLC68JRH settings that areretrieved from OTP memory at power-up. Values eventually changed via I2C registers are lost if the receivermodule is removed from the transmitter, unless VOUT or VRECT rails are externally kept above 4V (e.g. as perFigure 7b).

Table 2. Receiver module default settings

Parameter Default setting

Output voltage 5.0 V

Minimum VRECT 4 V (output is disconnected if VRECT voltage is lower than this value)

Dummy load 40 mA (minimum load current to ensure ASK communication stability)

Nominal chip idle current consumption 17 mA (application dependent)

Output current threshold for deeper ASKmodulation

100 mA (if the output current is higher than this value, auxiliarymodulation pins CLAMP1 and CLAMP2 are activated)

GPIO0 pin function Open drain, low when output is enabled (D3 LED)

INT pin function Open-drain, low in case of over-temperature, over-current or over-voltage condition.

Over-Temperature protectionLower 80°C threshold leading to output disconnection and EPT

generation to terminate power transfer. Upper 125°C threshold leading toAC1 and AC2 pins short-to-ground.

Over-Voltage protection (VRECT rail)Lower 12 V threshold leading to temporary IEXT activation (VRECT

clamping). Upper 25 V threshold leading to AC1 and AC2 pins short-to-ground.

Over-Current protection 1.5 A threshold leading to output disconnection and EPT generation toterminate the power transfer.


UM2693 - Rev 1 page 4/18

As already mentioned, a LED (D3) is connected to GPIO0 and it is used as output state monitor: it turns-on whena correct power transfer is established between the receiving module and the transmitter, and the output voltageis enabled. All the settings shown in table 2 (and other additional ones) can be modified in the registers page ofthe GUI (see the related GUI user manual for details).

Table 3. Receiver module bill of material

Component Value Description Part Number Manufacturer

L1 11.8µH RX coil, 15 mm 760308101219 Wurth

C1, C2, C3 47nF ±10%

MLCC, X7R, 50V,0402

GRM155R71H473KE14D

Murata

C4 100nF ±10% GCM155R71H104KE02D

C5 1.8nF ±5% GRM155R71H182JA01D

C7, C8, C10, C11 47nF ±10% GRM155R71H473KE14D

C12 4n7 ±10% GCM155R71H472KA37D

C6, C9 22nF ±10% GRM155R71H223KA12D

C13, C14 2.2µF ±10% MLCC, X5R, 25V,0402 GRM155R61E225KE11D Murata

C15, C16, C17, C18,C19, C20 10µF ±20% MLCC, X5R, 25V,

0603 GRM188R61E106MA73D Murata

D1, D2 12V Uni-directional TVS,SOD882 PESD12VS1UL NXP

D3 Red LED, 0402 SML-P12VTT86R Rohm

R1 100R ±5% Anti-surge resistor,0.25 W, 0603 CRGP0603F100R TE Connectivity

R2 470R ±5%Resistor, 0.1 W, 0201

R3, R4, R5 47k ±5%

U1 Wireless powerreceiver, CSP-72 STWLC68JRH STMicroelectronics


UM2693 - Rev 1 page 5/18

2 USB to I2C bridging dongle

OverviewThe USB to I2C bridging dongle is the tool that allows interfacing the receiver to the Graphical User Interfacerunning on a PC. The P2 connector signals are summarized in Table 4. Three LEDs monitor the operation of thebridge: D1 (green) indicates I2C bus activity, D2 (red) indicates correct initialization of the U1 chip and 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 bridging dongle top view

Figure 6. USB-to-I2C bridging dongle schematic

1

1

2

2

3

3

4

4

D D

C C

B B

A A

Title

Number RevisionSize

A4

Date: 14.2.2020 Sheet ofFile: C:\Projects\..\STEVAL-ISB68I2C.SchDoc Drawn By:

I2C communication

GND

GND

470nF

C4

GND1MR1

100nFC5

GND GND GND

MCP_RSTBMCP_INTB I/O11

GND2

I/O23 I/O2 4VBUS 5I/O1 6U3

USBCL6-2

GP01

GP12

RST3

URx4

UTx

5

GP2

6

GP3

7

SDA

8

SCL 9VUSB 10D- 11D+ 12VSS

13N

C14

NC

15V

DD

16U1

MCP2221

RST

VBUS1

D-2

D+3

ID4

GND5

ShieldShell

P1

MicroUSB

VBUS

VD

D

VD

D

GND

100nFC1

2.2uFC3

GND GND

VBUS

1uFC2

GND

VDDVIN1

INHIBIT3 NC 4

VOUT 5

GN

D2

U2

LD2981

220RR7

D1LED

VDD

D2LED

220RR6

D3LED

470RR5

GND

VB

US

S1SW-SPST100nF

C6

RST

GND

GP2

GP3

GP2

GP3

SDA

SCL

4k7R2

4k7R3

VD

D

VD

D

SDA

SCL

123456

P2

Header connector

GNDSDASCLMCP_INTBRSTB

VBUS

4k7R4

VD

DM

CP_

INTB

D4

STPS1L60ZFY

F1

Littelfuse 0603L025

G

SD

32

1

Q1FDV303N

GND

RSTB

MCP_RSTB

100kR8

4k7R9

VD

D

STEVAL-USBI2C

Table 4. USB-to-I2C bridging dongle P2 connector

Pin Signal Description

1 GND Common return (ground)

2 SDA I2C bus, SDA line

3 SCL I2C bus, SCL line

4 INTB I/O line dedicated to INT pin management (status reading)

5 RSTB Reset signal for the STWLC68JRH chip, active low. Not used in the receivermodule.

UM2693USB to I2C bridging dongle

UM2693 - Rev 1 page 6/18

Pin Signal Description

6 VBUS

Auxiliary supply rail. Used to supply the STWLC68JRH chip via VOUT whenthe receiver module is not placed on a transmitter. The D4 diode (see

Figure 6) avoids backflow toward the USB supply rail when VOUT is higherthan 5V.

The receiver module must be connected to the dongle as shown in Figure 7a: the P2 connector of the receiverengages with the corresponding 4 signals of the P2 connector of the dongle. The communication over the I2C busis possible only if the STWLC68JRH chip of the receiver is powered: when not placed on a transmitter, thereceiver module can be powered through VOUT by wiring it to the VBUS pin of P2 (Figure 7b). This way ofpowering the receiver module is also required during OTP memory flashing.

Figure 7. Connection between receiver module and dongle

Table 5. USB-to-I2C bridging dongle bill of material


C1, C5, C6 100nF ±10% MLCC, X7R, 50V,0402 GCM155R71H104KE02D Murata

C2 1uF ±10% MLCC, X7R, 25V,0402 GRM155R61E105KA12D Murata

C3 2.2uF ±20% MLCC, X7R, 6.3V,0402 GRM155R60J225ME95D Murata

C4 470nF ±10% MLCC, X7R, 16V,0402 GRM155R61C474KE01D Murata

D1 Red LED, 0603 150060VS55040 Wurth Elektronik

D2 Green LED, 0603 150060RS55040 Wurth Elektronik

D3 Yellow LED, 0603 150060YS55040 Wurth Elektronik

D4 Schottky diode, 60V,1A, SOD123 STPS1L60ZFY STMicroelectronics

R1 1M ±5%

Resistor, 0.1W, 0402

R2, R3, R4, R9 4k7 ±5%

R5 470R ±5%

R6, R7 220R ±5%

R8 100k ±5%

Q1 N-channel MOSFET,25V, 0.6A, SOT23 FDV303N ON-Semi


UM2693 - Rev 1 page 7/18


P2 Pin header, 2.54 mmpitch

U2 3.3V, 100 mA, Linearregulator, SOT23-5L LD2981CM33TR STMicroelectronics

F1 Fuse, 0.25A, 0603 0603L025 Littelfuse

U1 USB to I2Cconverter, QFN16 MCP2221A-I/ML Microchip

U2Linear regulator,3.3V, 100 mA,

SOT23-5LLD2981CM33TR STMicroelectronics

U3 ESD suppressor,SOT23 USBCL6-2SC6 STMicroelectronics

P1 Micro-USB connector 629105150921 Wurth Elektronik

S1 SMT tactile switch,6mm x3.5 mm P-DT2112C Diptronic


UM2693 - Rev 1 page 8/18

3 STEVAL-ISB68WA test setup

The evaluation of the STEVAL-ISB68WA kit relies on a suitable wireless power transmitter that could mate withthe coil of the RX module. A good coupling factor is essential for both power transfer efficiency and datacommunication reliability between the transmitter and the receiver.The STEVAL-ISB045V1 wireless power transmitter evaluation kit contains the reference transmitter for the testsetup. The complete test setup is shown in Figure 8.

Figure 8. STEVAL-ISB68WA evaluation setup

The receiver is connected to the dongle as per Figure 7a and placed on the transmitter.

Note: The transmitter must be configured (through its own GUI) to have a ping frequency of 120 kHz and a 130 kHz-170 kHz operating frequency range. These parameters are easily unlocked and configured in the “parameters”window (Figure 9).

UM2693STEVAL-ISB68WA test setup

UM2693 - Rev 1 page 9/18

Figure 9. Configuration of the transmitter

As soon as the LED on the receiver lights up, its control GUI can be launched. Connectivity with theSTWLC68JRH is automatically verified and the chip info (IDs content) is shown in the registers page (Figure 10).


UM2693 - Rev 1 page 10/18

Figure 10. Graphical User Interface registers page showing chip IDs

To monitor the operation of the receiver, a real-time plotting of key parameters can be selected: in Figure 11 theVRECT and VOUT voltages, the temperature of the rectifier (TRECT) and its output current (ISNS) are shown.

Figure 11. Graphical User Interface charts page plotting a variable output load


UM2693 - Rev 1 page 11/18

The load at VOUT can be increased up to 2.5 W. A 10 Ω purely resistive load (i.e. 2.5 W load at 5 V) is usuallymanaged without problems also at ping-up. In some case (e.g. a following DC-DC converter stage) the load couldshow a remarkable capacitive behavior and a relatively high initial current may trigger the over-current protectionor may exceed the dynamic capability of the transmitter. To avoid this, the load should be smoothly increased, orits capacitive component should be reduced.Several parameters of the receiver module can be temporary changed through the GUI. Just to give an example,the output voltage can be changed on-the-fly by acting on the slider and writing the new value into the relatedregister (Figure 12).

Figure 12. Changing the output voltage to 6 V via GUI

Note that increasing the output voltage may impact on the external components (e.g. proximity to maximumvoltage rating of VRECT and VOUT capacitors or to clamping voltage of protection TVS diodes) and on somesetting (the OVP threshold, for example, could be triggered if not conveniently adapted to the new operatingconditions). Some transmitters may have inherent limitations and could terminate the power transfer if significantchanges in the output voltage are applied.An extensive description of the GUI and its functionalities can be found in the related user manual, while thecomplete register map of STWLC68JRH can be found in its datasheet.Figure 13 reports the typical TX-to-RX efficiency of the paired STEVAL-ISB68WAM and STEVAL-ISB045V1T kits.Although the graph in Figure 13 has been extended to an output power of 3.5 W (0.7 A @ 5 V), the 2.5 W limitprevents over-heating of the RX coil.


UM2693 - Rev 1 page 12/18

Figure 13. Transmitter input to receiver output overall efficiency


UM2693 - Rev 1 page 13/18

Revision history

Table 6. Document revision history

Date Version Changes

19-Feb-2020 1 Initial release.

UM2693

UM2693 - Rev 1 page 14/18

Contents

1 Wireless power receiver module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

2 USB to I2C bridging dongle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

3 STEVAL-ISB68WA test setup. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

List of tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

List of figures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

UM2693Contents

UM2693 - Rev 1 page 15/18

List of tablesTable 1. Receiver module terminals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Table 2. Receiver module default settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Table 3. Receiver module bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Table 4. USB-to-I2C bridging dongle P2 connector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Table 5. USB-to-I2C bridging dongle bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Table 6. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

UM2693List of tables

UM2693 - Rev 1 page 16/18

List of figuresFigure 1. Receiver module. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Figure 2. Receiver module schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Figure 3. Receiver module top and bottom silkscreen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Figure 4. Receiver module wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Figure 5. USB-to-I2C bridging dongle top view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Figure 6. USB-to-I2C bridging dongle schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Figure 7. Connection between receiver module and dongle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Figure 8. STEVAL-ISB68WA evaluation setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Figure 9. Configuration of the transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Figure 10. Graphical User Interface registers page showing chip IDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Figure 11. Graphical User Interface charts page plotting a variable output load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Figure 12. Changing the output voltage to 6 V via GUI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Figure 13. Transmitter input to receiver output overall efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

UM2693List of figures

UM2693 - Rev 1 page 17/18

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UM2693

UM2693 - Rev 1 page 18/18

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Getting started with STEVAL-ISB68WA wireless power