NXP Semiconductors WCT1012 Manuale utente

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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

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

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

NXP Semiconductors 3

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

4 NXP Semiconductors

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

6 NXP Semiconductors

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

NXP Semiconductors 7

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

8 NXP Semiconductors

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

NXP Semiconductors 9

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

10 NXP Semiconductors

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：



      

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