ST STEVAL-ISB68WA User manual

Introduction
The STEVAL-ISB68WA is an evaluation kit based on STWLC68JRH wireless power receiver and it is designed as reference
solution for wearable applications. The kit consists of a wireless receiver module and USB-to-I2C bridging dongle. The receiver
is a 3-elements stack: a PCB housing the STWLC68JRH wireless power receiver and all the required external components, a 2
mm 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 of
the box when placed on a suitable wireless power transmitter.An on-board LED indicates when the communication with the
transmitter succeeds and the power transfer is in progress.Thanks to the I2C interface, the module can be easily controlled and
configured 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 spaced
to 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 2020
For further information contact your local STMicroelectronics sales office.
www.st.com

1Wireless power receiver module
Overview
As 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 the
AC1-AC2 pins of the STWLC68JRH. The rectified voltage is filtered by C15 through C17 capacitors and
accessible 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 additional
components are needed to complete the wireless receiver: bootstrap capacitors for the rectifier (C8 & C11) and
for the main linear regulator (C12), modulation capacitors (C6, C7, C9 and C10) and filtering capacitors for the 1.8
V and 5 V supply rails (C13 & C14). The R1 resistor is connected between VRECT and IEXT to implement an
active 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
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The terminals for the receiving coil, the output load and the control signals are summarized in Table 1. The output
rail and the control interface are already made easily accessible by means of wires terminated with pin header
female 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
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Wireless power receiver module
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Figure 4. Receiver module wiring
Additional control signals and programmable general-purpose I/O pins are available at the STWLC68JRH, but
they are not used in the module to keep the reference solution as simple as possible. The STWLC68JRH chip can
handle up to 400 kHz speed over the I2C bus. Table 2 summarizes the default STWLC68JRH settings that are
retrieved from OTP memory at power-up. Values eventually changed via I2C registers are lost if the receiver
module is removed from the transmitter, unless VOUT or VRECT rails are externally kept above 4V (e.g. as per
Figure 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 ASK
modulation
100 mA (if the output current is higher than this value, auxiliary
modulation 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 protection
Lower 80°C threshold leading to output disconnection and EPT
generation to terminate power transfer. Upper 125°C threshold leading to
AC1 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 to
terminate the power transfer.
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Wireless power receiver module
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As already mentioned, a LED (D3) is connected to GPIO0 and it is used as output state monitor: it turns-on when
a correct power transfer is established between the receiving module and the transmitter, and the output voltage
is enabled. All the settings shown in table 2 (and other additional ones) can be modified in the registers page of
the 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 power
receiver, CSP-72 STWLC68JRH STMicroelectronics
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Wireless power receiver module
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2USB to I2C bridging dongle
Overview
The USB to I2C bridging dongle is the tool that allows interfacing the receiver to the Graphical User Interface
running on a PC. The P2 connector signals are summarized in Table 4. Three LEDs monitor the operation of the
bridge: 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 of
File: C:\Projects\..\STEVAL-ISB68I2C.SchDoc Drawn By:
I2C communication
GND
GND
470nF
C4
GND
1M
R1
100nF
C5
GND GND GND
MCP_RSTB
MCP_INTB I/O1
1
GND
2
I/O2
3I/O2 4
VBUS 5
I/O1 6
U3
USBCL6-2
GP0
1
GP1
2
RST
3
URx
4
UTx
5
GP2
6
GP3
7
SDA
8
SCL 9
VUSB 10
D- 11
D+ 12
VSS 13
NC 14 NC 15
VDD 16
U1
MCP2221
RST
VBUS
1
D-
2
D+
3
ID
4
GND
5
Shield
Shell
P1
MicroUSB
VBUS
VDD
VDD
GND
100nF
C1
2.2uF
C3
GND GND
VBUS
1uF
C2
GND
VDD
VIN
1
INHIBIT
3NC 4
VOUT 5
GND
2
U2
LD2981
220R
R7
D1
LED
VDD
D2
LED
220R
R6
D3
LED
470R
R5
GND
VBUS
S1
SW-SPST
100nF
C6
RST
GND
GP2 GP3
GP2 GP3 SDA
SCL
4k7
R2
4k7
R3
VDD VDD
SDA SCL
1
2
3
4
5
6
P2
Header connector
GND
SDA
SCL
MCP_INTB
RSTB
VBUS
4k7
R4
VDDMCP_INTB
D4
STPS1L60ZFY
F1
Littelfuse 0603L025
G
S D 32
1
Q1
FDV303N
GND
RSTB
MCP_RSTB
100k
R8
4k7
R9
VDD
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 receiver
module.
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USB to I2C bridging dongle
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Pin Signal Description
6 VBUS
Auxiliary supply rail. Used to supply the STWLC68JRH chip via VOUT when
the receiver module is not placed on a transmitter. The D4 diode (see
Figure 6) avoids backflow toward the USB supply rail when VOUT is higher
than 5V.
The receiver module must be connected to the dongle as shown in Figure 7a: the P2 connector of the receiver
engages with the corresponding 4 signals of the P2 connector of the dongle. The communication over the I2C bus
is possible only if the STWLC68JRH chip of the receiver is powered: when not placed on a transmitter, the
receiver module can be powered through VOUT by wiring it to the VBUS pin of P2 (Figure 7b). This way of
powering 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
Component Value Description Part Number Manufacturer
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
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Component Value Description Part Number Manufacturer
P2 Pin header, 2.54 mm
pitch
U2 3.3V, 100 mA, Linear
regulator, SOT23-5L LD2981CM33TR STMicroelectronics
F1 Fuse, 0.25A, 0603 0603L025 Littelfuse
U1 USB to I2C
converter, QFN16 MCP2221A-I/ML Microchip
U2
Linear regulator,
3.3V, 100 mA,
SOT23-5L
LD2981CM33TR 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
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3STEVAL-ISB68WA test setup
The evaluation of the STEVAL-ISB68WA kit relies on a suitable wireless power transmitter that could mate with
the coil of the RX module. A good coupling factor is essential for both power transfer efficiency and data
communication reliability between the transmitter and the receiver.
The STEVAL-ISB045V1 wireless power transmitter evaluation kit contains the reference transmitter for the test
setup. 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).
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STEVAL-ISB68WA test setup
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Figure 9. Configuration of the transmitter
As soon as the LED on the receiver lights up, its control GUI can be launched. Connectivity with the
STWLC68JRH is automatically verified and the chip info (IDs content) is shown in the registers page (Figure 10).
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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 the
VRECT 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
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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 usually
managed without problems also at ping-up. In some case (e.g. a following DC-DC converter stage) the load could
show a remarkable capacitive behavior and a relatively high initial current may trigger the over-current protection
or may exceed the dynamic capability of the transmitter. To avoid this, the load should be smoothly increased, or
its 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 related
register (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 maximum
voltage rating of VRECT and VOUT capacitors or to clamping voltage of protection TVS diodes) and on some
setting (the OVP threshold, for example, could be triggered if not conveniently adapted to the new operating
conditions). Some transmitters may have inherent limitations and could terminate the power transfer if significant
changes in the output voltage are applied.
An extensive description of the GUI and its functionalities can be found in the related user manual, while the
complete 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 limit
prevents over-heating of the RX coil.
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Figure 13. Transmitter input to receiver output overall efficiency
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Revision history
Table 6. Document revision history
Date Version Changes
19-Feb-2020 1 Initial release.
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Contents
1Wireless power receiver module ...................................................2
2USB to I2C bridging dongle ........................................................6
3STEVAL-ISB68WA test setup .......................................................9
Revision history .......................................................................14
Contents ..............................................................................15
List of tables ..........................................................................16
List of figures..........................................................................17
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Contents
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List of tables
Table 1. Receiver module terminals .............................................................3
Table 2. Receiver module default settings .........................................................4
Table 3. Receiver module bill of material ..........................................................5
Table 4. USB-to-I2C bridging dongle P2 connector ...................................................6
Table 5. USB-to-I2C bridging dongle bill of material ..................................................7
Table 6. Document revision history ............................................................. 14
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List of figures
Figure 1. Receiver module...................................................................1
Figure 2. Receiver module schematic ...........................................................2
Figure 3. Receiver module top and bottom silkscreen ................................................3
Figure 4. Receiver module wiring ..............................................................4
Figure 5. USB-to-I2C bridging dongle top view .....................................................6
Figure 6. USB-to-I2C bridging dongle schematic ...................................................6
Figure 7. Connection between receiver module and dongle ............................................7
Figure 8. STEVAL-ISB68WA evaluation setup .....................................................9
Figure 9. Configuration of the transmitter ........................................................ 10
Figure 10. Graphical User Interface registers page showing chip IDs ..................................... 11
Figure 11. Graphical User Interface charts page plotting a variable output load .............................. 11
Figure 12. Changing the output voltage to 6 V via GUI ............................................... 12
Figure 13. Transmitter input to receiver output overall efficiency ......................................... 13
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List of figures
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