NXP Semiconductors WCT1012 User manual

© 2017 NXP B.V.
_______________________________________________________________________
WCT1012 15W Single Coil TX V3.1
Reference Design System User’s
Guide
1Introduction
This document describes how to use the 15W
medium power wireless charger transmitter
WCT-15W1COILTX (MPA4) reference board
designed by NXP. The reference solution is
compliant with Qi Medium Power V1.2.2
specification. It is a low-cost reference solution,
which can be easily customized through the
FreeMASTER GUI tool.
Figure 1. WCT-15W1COILTX reference board
Contents
1Introduction 1
2System Features 2
3Package Checklist 2
4System Block Diagram 2
5Hardware Description 3
6Foreign Object Detection Architecture 6
7Getting Started 11
8Flash Extension of WCT1011 42
9References 45
NXP Semiconductors
Document Number: WCT1012V31SYSUG
User’s Guide
Rev. 0
,
02/2017

WCT1012 15W Single Coil TX V3.1 Reference Design System User’s Guide, Rev. 0, 02/2017
2 NXP Semiconductors
2 System Features
The WCT-15W1COILTX reference board has these features:
Compliant with the Qi Medium Power v1.2.2 specification
Integrated digital demodulation in chip
Supports multiple types of RX modulation signals (AC capacitor, AC resistor, and DC
resistor)
Supports two-way communication
Supports FOD based on quality factor (Q factor) change
Supports FOD based on calibrated power loss accounting
Supports Qi MP receiver with 15W output power capability
Supports Qi LP receiver with 5W output power capability
Super low standby power
Supports switch between full bridge topology and half-bridge topology
Supports frequency control, phase shift control, and duty control algorithm
Supports WPID
LED for system status indication
Input voltage, input current, and coil current sensing
FreeMASTER GUI tool to enable customization and calibration
3Package Checklist Table 1. Package checklist
Name
Count
WCT-15W1COILTX board
1
4System Block Diagram
MP TX runs with RX to transfer power from TX to RX as well as send messages to RX by frequency shift
keyed modulation (FSK), as shown in this figure.
Figure 2. Wireless Charging System overview

WCT1012 15W Single Coil TX V3.1 Reference Design System User’s Guide, Rev. 0, 02/2017
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To find WPC Qi information, visit www.wirelesspowerconsortium.com/developers/.
5 Hardware Description
5.1 Reference board block diagram
Figure 3. Block diagram

WCT1012 15W Single Coil TX V3.1 Reference Design System User’s Guide, Rev. 0, 02/2017
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5.2 Modules explanation
Figure 4. WCT_MP board modules overview
Controller
The NXP WCT1012 chip is the central controller of WCT-15W1COILTX board. It has rich
peripherals with low power consumption. It processes communication signals, controls power
transfer start/stop, and controls a full bridge PWM inverter for output power control.
These are the peripherals used in this application:
oTwo PWM channels for full bridge DC/AC inverter control
oThree Timers for system timing and communication
oADCs for input voltage and current, coil current sampling, temperature sensing, and
quality factor detecting
oDAC for generate reference voltage for LDO to produce driver signal for the quality factor
detecting circuit
oGPIOs for pre-drivers control, LED control, and multiplexer switch control
WCT1012
Input 12V DC
AUX Power
FB Inverter
JTAG Connector
To the coil
UART COM port
Input current
sensing
Q factor measurement
circuit

WCT1012 15W Single Coil TX V3.1 Reference Design System User’s Guide, Rev. 0, 02/2017
NXP Semiconductors 5
oSCI for serial port debugging or debug console
Inverter
The full bridge PWM control inverter converts 12 V DC input voltage to a higher AC voltage.
oFor charging LP RX, the PWM frequency follows the WPC Qi specification. In the 110
KHz–205 KHz range with half bridge, lower frequency outputs larger power with 50%
PWM duty and starts duty control (50%–10%) when the frequency reaches 205 KHz.
oWhen charging MP RX, TX works with half bridge in the 172 KHz–205 KHz frequency
range and starts phase control (16%–100%) at 172 KHz. When PWM phase shift reaches
100%, TX works in full bridge frequency control mode in the range of 110 KHz–172 KHz
with 50% PWM duty. Lower frequency outputs larger power and starts duty control
(50%–10%) when the frequency reaches 205 KHz.
Input voltage range: 11 V DC–13 V DC
Communication
oCommunication from RX to TX: The communication of 2 kbps signal is demodulated from
high frequency coil current AC signal (110 KHz–205 KHz). The RC sensing circuit gets
resonant coil current and input to ADC for sampling. The digital demodulation module
processes the input samples and extracts communication packets.
oCommunication from TX to RX: TX shall negotiate with RX in the negotiation phase if
requested by RX. TX uses FSK modulation to communicate to RX, and the communication
frequency is about 512 times power signal frequency.
Q factor detecting
oWhen the medium RX is put on the interface of TX, TX starts to detect Q factor of the coil.
If Q factor is lower than the threshold, which is determined by RX reported Q factor, FO is
detected. This method can detect FO before power transfer.
oThere are two methods of Q factor detection methods provided in this release: free
resonance and external driver, which need different hardware modules as shown in Figure
5-a and Figure 5-b. The Q Factor measurement circuit is also different. See Section 6.1 for
detailed information.
Figure 5-a. Free resonance Q measurement
Figure 5-b. External driver Q measurement

WCT1012 15W Single Coil TX V3.1 Reference Design System User’s Guide, Rev. 0, 02/2017
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6Foreign Object Detection Architecture
The NXP WCT-15W 1COIL TX solution provides two methods of Foreign Object Detection: FOD based
on quality factor (Q factor) change and FOD based on power loss accounting. The former can detect FO
before power transfer and the later can work during power transfer phase.
6.1 FOD based on Q factor change
A change in the environment of the TX coil typically causes its inductance to decrease and its equivalent
series resistance to increase. Both effects lead to a decrease of the TX coil’s Q factor. The RX would send
a packet including the reference Q factor for TX to compare and determine if FO exists, as shown in
Figure 6.
The reference Q factor is defined as the Q factor of Test Power Transmitter #MP1’s Primary Coil at an
operating frequency of 100 kHz with RX positioned on the interface surface and no FO nearby. Due to the
differences between its design and that of Test Power Transmitter #MP1, the difference between the
frequency it uses to determine its Q factor and 100 kHz, TX needs to convert the Q factor it measured to
that of Test Power Transmitter #MP1. NXP provides the conversion method and needs to get the
parameters on board at first. The TX would do auto-calibration and get parameters the first time power up
after flashing a new image, and then these parameters are written to flash. Therefore, it is necessary to
make sure there is no object on the TX surface the first time powering up after flashing a new image.
Figure 6. Quality factor threshold example

WCT1012 15W Single Coil TX V3.1 Reference Design System User’s Guide, Rev. 0, 02/2017
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The NXP WCT-15W1COILTX provides two optional methods to detect Q factor: free resonance and
external driver. The free resonance method is enabled by default in the released V3.1 f/w. To apply
free resonance method, the WCT-15W1COILTX Rev.3 board (SCH-28122 REVC3, 700-28122
REVA) needs rework. The external driver method could be applied on the WCT-15W1COILTX
Rev.3 board directly. Customers can apply external driver Q factor detection by changing the related
macro to enable it as follows:
#define QF_EXTERNAL_DRIVER TRUE
#define QF_FREE_RESONANCETRUE FALSE
6.1.1 Free Resonance Q factor
The free resonance Q factor detection aims to detect the decay rate of the resonance signal, as shown in
Figure 7. With the system’s high Q, driving just a few pulses near resonant frequency is sufficient to serve
as an impulse and start the system ringing. The decay rate of the signal can be found by collecting the
ADC data of the tank voltage (or coil current).
Q=/(-ln(Rate))
Rate is the decay rate value of the resonance signal.
Figure 7. Resonance signal
The circuit for free resonance Q measurement is as shown in Figure 8, which is sampling circuit of signal
on resonance capacitors.

WCT1012 15W Single Coil TX V3.1 Reference Design System User’s Guide, Rev. 0, 02/2017
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Figure 8. Free resonance Q measurement circuit
6.1.2 External Driver Q factor
The external driver Q factor detection method is described as shown in Figure 9.It consists of a series
connection of the coil and a resonance capacitor that is driven by a sinusoidal voltage. The capacitance
value of the resonance capacitor is chosen so that the resonance frequency of the system is in a suitable
range. In this example, the resonance frequency is 100 kHz. The Q factor of the coil follows from this
system as the ratio of the RMS voltage across the coil and the RMS voltage that is driving the system at the
resonance frequency.
Q = 
/ (at resonant frequency)
Figure 9. External Driver Q factor measurement method
The sample circuits include driver signal sampling and resonance signal sampling, as shown in Figure 10:

WCT1012 15W Single Coil TX V3.1 Reference Design System User’s Guide, Rev. 0, 02/2017
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Figure 10. External driver Q measurement circuit
The driver signal should be small to avoid waking up the RX during Q factor measurement. Therefore, it is
necessary to use an auxiliary power to generate a low voltage for the driver signal.
6.2 FOD based on power loss accounting
The power loss , which is defined as the difference between the Transmitted Power  and the
Received Power, i.e.    , provides the power absorption in Foreign Objects, as shown
in the following figure.
Figure 11. Power loss illustrated

WCT1012 15W Single Coil TX V3.1 Reference Design System User’s Guide, Rev. 0, 02/2017
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When FO is implemented in the power transfer, the power loss increases accordingly. Then the FO can be
detected based on the power loss method.
Power loss FOD method is divided into two types:
FOD for baseline power profile (TX and RX can transfer no more than 5W of power)
Extensions power profile (TX and RX can transfer power above 5W)
6.2.1 Power loss FOD baseline
The equation for power loss FOD baseline is    .
The Transmitted Power  represents the amount of power that leaves TX due to the magnetic field of
the TX, and     , where the  represents the input power of TX and  is the
power dissipated inside the TX.  can be calculated by sampling input power and input current, and
 can be estimated through coil current.
The Received Power  represents the amount of power that is dissipated within the RX due to the
magnetic field of the TX, and     . The power  is provided at the RX’s output and
 is the power lost inside the RX.
When the NXP 15W 1COIL TX charges the RX baseline, the power loss baseline is applied. The TX
would continuously monitor the , and if it exceeds the threshold several times, the TX would
terminate power transfer.
6.2.2 Power loss FOD extensions
Typically, the RX estimates the power loss inside itself to determine its Received Power. Similarly, the
TX estimates the power loss inside itself to determine its Transmitted Power. A systematic bias in these
estimated results in a difference between the Transmitted power and the Received Power, even if there is
no Foreign Object present on the Interface Surface. To increase the effectiveness of the power loss
method, the TX can remove the bias in the calculated power loss by calibration. For this purpose, the TX
and RX execute the calibration phase before the power transfer phase starts. The TX needs to verify that
there is no FO present on its interface surface before calibration phase and pre-power FOD based on Q
factor can work.
Because the bias in the estimates can be dependent on the power level, the TX and RX determine their
Transmitted Power and Received Power at two load conditions—a “light” load and a “connected” load.
The “light” load is close to the minimum expected output power, and the “connected” load is close to the
maximum expected output power. Based on these two load conditions, the Power Transmitter can
calibrate its Transmitted Power using linear interpolation. Alternatively, the Power Transmitter can
calibrate the reported Received Power.
Take the calibrated Transmitted Power as an example：

      