AN11695
NXQ1TXA5 one-chip 5 V Qi wireless transmitter
Rev. 1 — 3 August 2015
Application note
Document information
Info
Keywords
Abstract
Content
NXQ1TXA5, wireless charger, A11 Qi coils, low power
This application note describes the NXQ1TXA5 wireless charger solution
designed for A11 Qi coils. It is based on the NXP Semiconductors
NXQ1TXA5 fully integrated wireless power transmitter product for Qi
compliant 5 volt low-power transmitters.
NXP Semiconductors
AN11695
NXQ1TXA5 one-chip 5 V Qi wireless transmitter
Revision history
Rev
v.1
Date
20150803
Description
first issue
Contact information
For more information, please visit:
http://www.nxp.com
For sales office addresses, please send an email to:
salesaddresses@nxp.com
AN11695
All information provided in this document is subject to legal disclaimers.
© NXP Semiconductors N.V. 2015. All rights reserved.
Application note
Rev. 1 — 3 August 2015
2 of 29
NXP Semiconductors
AN11695
NXQ1TXA5 one-chip 5 V Qi wireless transmitter
1. Introduction
This application note describes the NXQ1TXA5 wireless charger solution designed for
A11 Qi coils. It is based on the NXP Semiconductors NXQ1TXA5 fully integrated wireless
power transmitter product for Qi compliant 5 V low-power transmitters.
The NXQ1TXA5 comes in a 5 mm
5 mm HVQFN32 package. It implements all the logic
and power electronics required to realize a compact ultra-low component count 5 W Qi
power transmitter application. To complete the whole application, only a handful of small
passive components and a charging coil are required. The application operates from a 5 V
power supply (e.g. a USB adapter).
In this application note guidelines are given for the implementation of a fully operating
wireless power transmitter. Electrical, thermal and compliance aspects are covered.
Recommendations for tuning and potential customizations are explained.
1.1 Features
•
Single-chip WPC1.1.2 Qi-compliant device for A5/A11/A12/A16 5 V single-coil
low-power transmitters
•
Operates from a 5 V supply
•
Integrated high-efficiency full-bridge power stage with low EMI radiation, meeting
EN55022 radiated and conducted emission limits
•
•
•
•
•
•
•
•
•
•
•
•
Very few external components required, minimizing cost, complexity, and board space
Extremely low-power receiver detection circuitry; standby power 10 mW (typical)
Power stage fully protected against overcurrent and overtemperature
Fully integrated accurate coil current measurement
Demodulates and decodes communication packages from Qi-compliant receivers
PID regulation for closed-loop power drive and control
Internal 1.8 V digital supply generation for the logic electronics
LED (2x) and buzzer outputs
NTC input for external temperature check and protection
On-chip thermal protection
Small HVQFN32 package (5 mm
5 mm) with 0.5 mm pitch
Foreign Object Detection (FOD) with automatic switching between V 1.1 and V 1.0 for
legacy receiver support
differences and meet Qi certification requirements
•
FOD levels can be adjusted using external resistors to compensate for application
•
Smart Power Limiting (SPL) function to adapt to power-limited 5 V supplies
•
Static Power Reduction (SPR) function for multiple NXQ1TXA5 on a single USB
supply
•
Supports Near Field Communication (NFC) TAG applications with delayed start-up
AN11695
All information provided in this document is subject to legal disclaimers.
© NXP Semiconductors N.V. 2015. All rights reserved.
Application note
Rev. 1 — 3 August 2015
3 of 29
NXP Semiconductors
AN11695
NXQ1TXA5 one-chip 5 V Qi wireless transmitter
2. Schematic, bill of materials, and layout
Figure 1
shows a full basic circuit diagram for a NXQ1TXA5 wireless power transmitter
application. The circuit diagram includes the status LED indicators and a connection for a
buzzer. They may be omitted if not required, but their connections are shown for the sake
of completeness. The same is true for the temperature sensors. One or more sensors can
be implemented in a specific application. However, it is also possible to omit the sensors
and in this way ignore specific temperature information. In this case, only the NXQ1TXA5
internal temperature protection remains intact.
Fig 1.
NXQ1TXA5 wireless power transmitter circuit diagram
A USB powered wireless power transmitter is a standard application for the circuit shown
in
Figure 1. Figure 2a
and
Figure 2b
show two potential implementations of the power
interface circuit.
Figure 2a
is only a buffer. However, with a proper layout the result is an
already very good EMI performance.
The circuit of
Figure 2b
contains an additional common mode choke (L3). This interface
actively contributes to maximizing EMI reduction. An additional LED (H3) shows that the
application is powered.
AN11695
All information provided in this document is subject to legal disclaimers.
© NXP Semiconductors N.V. 2015. All rights reserved.
Application note
Rev. 1 — 3 August 2015
4 of 29
NXP Semiconductors
AN11695
NXQ1TXA5 one-chip 5 V Qi wireless transmitter
The power drawn by the H3 LED must be low because the current flowing in the LED has
a negative impact on the standby current of the application. So a relatively high-ohmic
current limiting resistor (R42) is chosen (3.9 k).
a. 5 V USB power input circuit
Fig 2.
5 V USB input power interface options
b. 5 V USB input power circuit with EMI filter
2.1 Circuit description
2.1.1 Power transfer
The power transfer section is on the left-hand side in the circuit diagram. The NXQ1TXA5
IC contains a full (4-MOSFET) power bridge that drives the series-resonant network
consisting of capacitance C
p
(realized by connecting capacitors C3, C4, C5, and C6 in
parallel) in series with the transmitter coil L
p
(connected to terminals IND1 and IND2). The
NXQ1TXA5 regulates the amount of power that the coil transmits by varying the switching
frequency of the bridge. At high frequency (e.g. 205 kHz), power transfer is low and at low
frequency (e.g. 110 kHz), power transfer is high.
If at 205 kHz switching frequency the power transfer is still higher than required by the
load, the NXQ1TXA5 IC reduces the operation duty cycle to arrive at the required power
transfer level. During the on-period of the duty cycle, the switching frequency is 205 kHz.
To limit ElectroMagnetic Interference (EMI), snubber networks are connected from the two
bridge-output nodes to ground (resistor R1/capacitor C1 and resistor R2/capacitor C2).
Supply decoupling of the power stage is implemented using capacitors C7, C8, C9, and
C10.
AN11695
All information provided in this document is subject to legal disclaimers.
© NXP Semiconductors N.V. 2015. All rights reserved.
Application note
Rev. 1 — 3 August 2015
5 of 29
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