Holtek WAS-1972EN User manual

Wireless Charging Sonic Electric Toothbrushes
WAS-1972EN V1.00 1 / 17 December 27, 2021
Wireless Charging Sonic Electric Toothbrushes
D/N: WAS-1972EN
Introduction
Wireless charging sonic electric toothbrushes are divided into two parts, a wireless charging
transmitter or charging base and a sonic electric toothbrush or toothbrush body. The charging base
mainly includes two functions, wireless charging transmission and ID identification. The toothbrush
body includes four functions, wireless charging reception, lithium battery charging/discharging
management, sonic motor control and LED indicators. The charging base is powered by a 5V USB
interface and provides power to the toothbrush body through LC resonance, which provides a one-
way communication function, so that the charging base can receive information and identify ID
information returned by the toothbrush body. The toothbrush body not only provides charging
management and LED capacity display functions during the charging process, but also controls the
sonic motor to execute the corresponding brushing mode according to the different setup operations.
The Holtek dedicated wireless charging MCU provides the required control signals mentioned
above. This application note will first introduce the operating principles of wireless charging and
then explain each function control process step by step. It allows users to have an increased
understanding of Holtek's wireless charging device.
Figure 1. System Block Diagram
Application Areas
Wireless charging sonic electric toothbrushes, wireless charging maglev razors.

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Solution Features
1. Few external components: includes an integrated demodulation circuit, an integrated high
voltage NMOS circuit and a linear charging management circuit.
Charging base master MCU: includes an integrated demodulation circuit and a high voltage
NMOS circuit.
The BP45F0044 provides an integrated high voltage NMOS circuit to control LC resonance.
An internal demodulation circuit together with an external current-sampling resistor can
implement wireless signal demodulation. The I/O outputs have a 4-level programmable current
function which can directly drive LEDs without the need for external components.
Toothbrush body master MCU: includes an integrated charging management circuit and an H-
bridge drive circuit.
The toothbrush body master MCU, the BP45F1330 includes an integrated linear charging
circuit which is used for lithium battery charging management. The device also includes an
integrated H-bridge drive circuit which can directly drive DC motors for backward or forward
control. The I/O outputs have a 4-level programmable current function which can directly
drive LEDs without the need for current limiting resistors.
2. Low power consumption: achieves power saving and automatic standby functions using ID
identification.
Charging base: achieves power saving function using ID identification.
An internal demodulation circuit together with an external current-sampling resistor can
implement wireless signal demodulation. The ID returned by the toothbrush body is used to
determine whether the charging base has been powered on. If the returned ID is incorrect, the
charging base will stop transmitting power to reduce the average system power consumption.
Toothbrush body: The toothbrush will automatically enter the standby mode if there is no
operation.
When entering operating mode 0, the toothbrush body will automatically enter the sleep mode
and the system will stop running. The average standby current is about 1µA to achieve to
reduce power consumption.
Operating Principles
A wireless charging function is based on the principle of transmitting power from a charging seat
to a toothbrush body in the way of a fluctuating magnetic field, allowing the toothbrush body to
sense an AC current. After the AC is sensed by the toothbrush body, it passes through a rectifier
circuit, after which the DC current can be used by the MCU and for lithium battery charging.
Communication also plays an important role in the wireless charging process. When a charging
base has successfully communicated with a toothbrush, the charging base will then transmit power.
When the power transmission function is not being used, the product enters the standby mode to
reduce power consumption. According to different toothbrush body setup operations, the sonic
motor can be controlled to swing from side to side with a corresponding amplitude and frequency
to achieve different cleaning effects.

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Functional Description
Solution Features
This solution consists of a charging base and a toothbrush body. Their characteristics will be
explained below.
Charging Base
Operating voltage: DC 5V – powered by a USB interface
Operating current: 160 mA – when connected to the toothbrush body
The charging base is powered by a 5V USB interface. LC resonance is implemented using a PWM
function to control the internal MOS transistors. An internal demodulation circuit together with an
external current-sampling resistor can implement communication demodulation. The ID returned by
the toothbrush body is used to determine whether the charging base is powered on.
Toothbrush Body
Operating voltage: DC 3.0V~4.2V – powered by a lithium battery
Operating current: Standby current consumption of 1µA (Sleep Mode), operating current
consumption of 600mA (LED + sonic motor)
Lithium battery charging management: The master BP45F1330 MCU includes an integrated
linear charging circuit which is used for lithium battery charging management. The H-bridge
drive circuit can directly drive the motor.
The toothbrush body is powered by an LC resonance circuit which is supplied to the MCU through a
regulator circuit. The internal linear charging circuit is used for 3.7 V lithium battery trickle charging,
constant current and constant voltage charging control. The charging current varies according to the
user design. During the charging process, the toothbrush body will communicate with the charging
base, which will obtain the toothbrush body ID.
Solution Functions
The application solution consists of a charging base and a toothbrush body. Figure 2 shows the
product hardware.
Sonic electric toothbrush
Button
Mode indicator
Charging indicator Charging base
Figure 2. Product Hardware

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Charging Base
The charging base is powered by a 5V USB interface. LC resonance is implemented using a PWM
function to control the internal MOS transistors. An internal demodulation circuit together with an
external current-sampling resistor can implement communication demodulation. The ID returned by
the toothbrush body is used to determine whether the charging base is powered on.
Toothbrush Body
The toothbrush body is mainly used to drive the sonic motor and to receive charging energy and
communication data from the charging base.
The sonic motor driver uses an integrated H-bridge drive circuit to control the sonic motor for
continuous backward or forward rotation control. The swing amplitude and force of the brush head
can be controlled by adjusting the pulse width when the motor rotates backward or forward. The
swing amplitude can be controlled by adjusting the pulse frequency.
The toothbrush body is powered by an LC resonance circuit which is supplied to the MCU through a
regulator circuit. The internal linear charging circuit is used for 3.7 V lithium battery trickle, constant
current and constant voltage charging control. The charging current varies according to the user design.
During the charging process, the toothbrush body will communicate with charging base, which will
obtain the toothbrush body ID. According to different toothbrush body setup operations, the sonic
motor is controlled to swing forwards and backwards with a corresponding amplitude and frequency
to achieve different cleaning effects. Each mode is described below.
Charging mode
The toothbrush body will enter the charging mode when it has been placed on the charging base.
When charging, the battery voltage of the toothbrush body will be less than 3.3V and the red
LED indicator will be on. When the battery voltage is greater than 3.3V but less than 3.8V, the
yellow LED indicator will be on. When the battery voltage is greater than 3.8V, the blue LED
indicator will be on and which will have a breathing illumination effect.
Operating modes
The toothbrush body has 4 different operating modes, which can be cyclically switched by a
button switch. In operating mode 0, which is the Sleep mode, the motor and LEDs will turn off.
Operating modes 1, 2 and 3 are used to implement different cleaning effects. Here three white
LEDs indicate the current operating mode.
Solution Design Description
This solution is composed of a charging base and a toothbrush body. The charging base uses the
BP45F0044 as a master MCU and provides 0.5K of Flash Program Memory, 4 bidirectional I/Os,
a high voltage NMOS, a programmable PWM circuit and a demodulation circuit. The toothbrush
body uses the BP45F1330 as a master MCU and provides 2 K of Flash Program Memory, 14
bidirectional I/Os and an H-bridge drive circuit.

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In terms of wireless charging transmission and data reception, the charging base uses a BP45F0044
integrated high voltage NMOS and a programmable PWM circuit to control the LC resonance
circuit to transmit wireless charging power. An integrated demodulation circuit is used to receive
wireless charging data. For the sonic motor and lithium battery charging control, the toothbrush
body uses a BP45F1330 integrated H-bridge drive circuit to control the sonic motor and uses an
integrated linear charging circuit for lithium battery charging management. The charging base and
toothbrush body hardware will be introduced below.
Hardware Description
Charging Base Hardware Block Diagram
Figure 3. BP45F0044 Charging Base Hardware Block Diagram
USB input
The charging base is a 5V voltage system, which uses a high voltage NMOS transistor to control
the LC resonance.
Integrated demodulation circuit
The current is converted to a voltage signal using an OCPI input pin and is amplified by an
internal programmable operational amplifier PGA and is demodulated using the appropriate
CMP settings and then finally used for communication.
Toothbrush Body Hardware Block Diagram
Figure 4. BP45F1330 Toothbrush Body Hardware Block Diagram

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Power input: After receiving the LC resonance energy signal transmitted by the charging base, the
toothbrush body will pass through a full-bridge rectifier circuit and a Zener regulator circuit, then
provide power to the BP45F1330 linear charging circuit.
Linear charger circuit: Select trickle/constant current/constant voltage charging modes by detecting
the battery voltage.
1. Trickle charging mode: During this initial charging process, for a battery that has been in an
over-discharged state, when the battery voltage is less than 2.5V, the battery will be pre-charged
at a constant current of 4mA. If the battery voltage is greater than 2.5V, the battery will be
charged at 0.1 times a constant current charging current (IB AT _ C C ) set by the firmware, that is,
0.1×IB AT _ C C .
2. Constant current charging mode: During this second stage, when the battery voltage is greater
than 3V, the battery will be charged using a constant current charging current, which is
controlled by the firmware.
3. Constant voltage charging mode: When the battery voltage is greater than 4.2V, it will be
charged using a constant voltage during this third stage. The charging current gradually
decreases as the constant voltage charging time increases. When the charging current is less than
0.1 times the constant current charging current, then the charging will cease.
Note: Here a 300mAh capacity lithium battery is taken as an example, 0.1C means charging at
30mA and 1C means charging at 300mA.
Modulation
During the charging process, the toothbrush will carry out one-way communication with the
charging base in the way of load change and transmits the ID code.
H-Bridge drive circuit
The integrated H-bridge drive circuit can control the sonic motor to rotate backward or forward.
Button
A button switch is used to switch the operating modes.
LEDs
Three white LEDs are used to display the operating modes and one RGB LED to display the
battery capacity.

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Hardware Circuit Diagram
Demodulation
circuit
Wireless charging circuit
Modulation
circuit
Battery
Sonic motor
LED indi cator
Figure 5. BP45F0044 and BP45F1330 Electric Toothbrush Solution Circuits
Layout and Hardware Considerations
Figure 6. Toothbrush Body PCB Layout
Figure 7. Charging Base PCB Layout

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PCB BOM Table
Tabl e 1. Toothbrush Body BOM
Tabl e 2. Charging Base BOM

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Coil Selection Description
Charging base coil
Inductance: 32.01µH
Coil turns: 10, multi-core enameled wire
Type: cylindrical, 8mm in height, 10mm in diameter, with magnetic column
Wire diameter: 0.6mm
Sonic electric toothbrush coil:
Inductance: 53.59µH
Coil turns: 18, single-core enameled wire
Type: cylindrical, 9mm in height, 15mm in diameter
Wire diameter: 0.3m
Charging Circuit Design Description
Toothbrush body input power protection design
Whether the lithium battery is fully charged or not, the charging base will both transmit the same
energy to the toothbrush body through the resonance circuit. Therefore, it is required to design a
front-end protection circuit. In order to prevent the toothbrush body MCU from being damaged
due to too high an energy level, it is necessary to design a full-bridge rectifier circuit and a Zener
diode at the front end.
This solution supports an operating current of about 45mA, an operating voltage of 5V and an
operating power of 0.225W. Therefore a 0.5W Zener regulator is selected. Refer to the application
note Wireless Charging Over Voltage Application Solutions for details (No. AN0532EN).
Parallel resonance frequency design
In this solution, the charging base coil inductance is 8.9µH, the default resonance frequency is
130kHz, the resonance capacitance is 168.41nF which is calculated by the LC resonance formula.
The LCFreq and PWMDuty parameters in the PWM program will be adjusted so that the PWM
output can switch at the zero point of the LC resonance waveform. The PWM frequency adjusted
by this solution is 114.3kHz and the toothbrush body inductance is 20µH. Here the resonance
capacitance of the toothbrush body is 96.97nF which is calculated based on the PWM frequency
of the charging base. For detailed adjustment methods and notes, refer to the application note
Wireless Charging Transmission Power Adjustment and Design (No. AN0558EN).
Software Description
Communication Mechanism Design
The communication method for this solution is based on load changes - changing load current. It will
include a resistor at the toothbrush body VIN and use a transistor to control it. When the transistor is
on, the load will increase and the charging base current will be larger. When the transistor is off, the
load will decrease and the charging base current will be smaller. Changes in current will allow the
charging base to receive these differences. The toothbrush body data signal will be decoded by circuits
such as a back-end amplifier and comparator.

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The corresponding settings should be prepared before the charging base communicates with the
toothbrush body, that is, the ID code of the charging base and the toothbrush body must be the same.
In the Holtek provided program, a fixed parameter of 2 bytes will be used as the ID code and 1 byte
of data will be used as user-defined data.
When configuring the toothbrush body, the following parameters will be found in the main program.
1. c_ID_H: Toothbrush ID code - high byte - fixed parameter
2. c_ID_L: Toothbrush ID code - low byte - fixed parameter
3. a_Rx_STA: a user-defined variable for the toothbrush body.
The charging base provides users with a set of complete and convenient ID identification functions. It
can also adjust the parameter settings such as the PWM operating time, ping time interval and
toothbrush body absence time. The toothbrush body has a user-defined 1 byte space for data
transmission such as toothbrush body state, battery voltage, etc. The following section will describe
the definable parameters.
1. c_ID_H: Charging base ID code - high byte - fixed parameter
2. c_ID_L: Charging base ID code - low byte - fixed parameter
3. c_PWM_ON_time: PWM ping operating time, unit is 10ms.
4. c_ping_cycle: PWM ping period (On + Off time), unit is 10ms.
5. c_time_out_after_success: The length of time after the toothbrush body is absent from the
charging base, it returns to a ping state, unit is 10ms.
6. c_OCPDA_offset: OCPDA offset calibration
Refer to the application note BP45F0044 Wireless Electric Toothbrush Application for detailed design
methods and notes (No. AN0569EN).
MCU Operating Environment
BP45F0044
VDD: 5V
Oscillator: 16MHz
Watchdog Timer: 1s
Timer: 50µs
BP45F1330
VDD: 5V
Oscillator: 8MHz
Watchdog Timer: 1s
Time Base: 200µs
Software Description
BP45F0044
ROM: 512×13 (use 499×13, percentage: 97%)
RAM: 32×8 (use 29×8, percentage: 90%)
OCP: demodulate with the appropriate debounce time when using the OCP for demodulation.
PWM: set the appropriate frequency and period to control LC resonance.
Timer: execute demodulation and timing once every 50µs when the flag is set.

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BP45F1330
ROM: 2K×14 - use 975×14, percentage: 47%
RAM: 64×8 - use 46×8, percentage: 71%
INT: key interrupt, external voltage input interrupt
Time Base: execute timing and state debounce functions every 200µs
LinearCharge: set constant current charging and charging over voltage protection
Timer: control the sonic motor to rotate backward or forward
ADC: read the battery voltage during discharging
Charging Base Main Flowchart Description
Start
Initialisation
OCP calibration
Demodulator subroutine
Has demodulated
successfully ?
Countdown is
completed ?
Begins a second countdown
for 2.5 seconds
PWM Off
Y
N
N
Y
Transmit a Ping signal
Transmit control subroutine
call PWM_ping_cycle
Automatically calibrate levels for
demodulation
call OCP_demo_trim
Demodulation data(ID code and data)
call Demodulation
Figure 8. BP45F0044 Charging Base Main Flowchart
1. Initialisation: RAM clear, GPIO initialisation, Timer setting, WDT setting and ID code setting.
2. Transmit a ping signal: The ping signal is transmitted after a delay of 0.4 seconds.
3. OCP calibration: automatic calibration at comparison points in the demodulation circuit.
4. Demodulation subroutine: parsing ID code and data to determine whether the ID code is correct.
5. Demodulated successfully: When the demodulation is successful, reset the 2.5-second countdown
timer. If this fails and the counter stops counting down, the PWM will be disabled.
6. Countdown has completed: The correct ID is required to be received within 2.5 seconds after a
successful demodulation operation, otherwise the PWM will be disabled and the program will be
executed again after 2.5 seconds.

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Toothbrush Body Main Flowchart Description
Start
Initialisation
Measure and process signals
Execute Toothbrush function
Control capacity display
Transmit codes during wireless charging
100ms Timer
1s Timer
Figure 9. BP45F1330 Toothbrush Body Main Flowchart
1. Initialisation: RAM clear, GPIO initialisation, Timer setting and WDT setting.
2. Measure and process signals: the MCU measures all input signals and executes debounce
operations. It also measures battery voltage.
3. Execute the toothbrush function: Refer to the toothbrush function execution subroutine description
below.
4. Transmit codes during wireless charging: During charging, transmit codes once at time intervals.
5. Control capacity display: Refer to the capacity display control subroutine description below.
6. 100ms Timer: Execute every 100ms to process the related timer flags.
7. 1s Timer: Execute every 1s to process the related timer flags

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Toothbrush Body Function Execution Subroutine Description
Execute Toothbrush
function
Charging？
End
N
The key has been
pressed？
Switch to the operating
mode 0
The operating m ode is
switched sequentially
0→1→2→3→0 ...
Load the corresponding time
parameter and
light the corresponding LED
Timer interrupt
Count value=0
End
Count value=1
Motor rotates forward
Update interrupt time
Count value=1
Count value=2
Count value=3
Motor stops
Update interrupt time
Count value=2
Motor rotates backward
Update interrupt time
Count value=3
Motor stops
Update interrupt time
Count value=0
N
N
Y
Y
Y
N
Y
N
Y
N
Y
N
Figure 10. BP45F1330 Toothbrush Operating Flowchart
Operating mode: There are four operating modes for the toothbrush body. After the operating mode is
executed, return to the main program immediately. If the MCU has entered the charging state, it will
be forcibly switched to operating mode 0. Each operating mode is described below.
1. Operating mode 0: Turn off the sonic motor and all LEDs.
2. Operating mode 1: Motor rotates for 1.08ms and stops for 0.42ms. Only white LED1 is always on.
3. Operating mode 2: Motor rotates for 1.08ms and stops for 1.08ms. Only white LED2 is always on.
4. Operating mode 3: Motor rotates for 1.52ms and stops for 0.72ms. Only white LED3 is always on.
Set the motor rotate/stop time in the main program and use the interrupt and counter to update the
interrupt time and motor action.

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Toothbrush Body Capacity Display Control Program Description
Contr ol battery
capacity display
The voltage is too
low?
Standby?
The red Led flashes
Battery
voltage>3.8V?
Battery
voltage>3.3V?
Turn off all LEDs
The blue Led is on
The yellow Led is on
Battery
voltage>3V?
End
The red Led is on
Low voltage warning Charging?
Breathing lamp control
Yes
Yes
Yes
Yes
Yes
Yes
No
No
No
No
No
No
Figure 11. BP45F1330 Toothbrush Capacity Display Flowchart
1. Low voltage: When the battery capacity is less than 5%, the red LED will flash and the motor will
vibrate 3 times as a warning. After the end, it will return to operating mode 0.
2. When the battery voltage is greater than 3.8V, the blue LED will be on. When the battery voltage
is greater than 3.3V, the yellow LED will be on. When the battery voltage is greater than 3V, the
red LED will be on.
3. During the charging process, the corresponding LEDs will be controlled with the breathing
illumination effect. This is a continuous process of alternating from fading to brightening.

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Library Description
The following table lists each API used by the toothbrush body.
Command Name
Functional Description
modulation_function()
Transmit toothbrush body ID and user-defined parameters
The following table details each API used by the toothbrush body.
API Name
modulation_function()
API Function
Transmit toothbrush body ID and user-defined parameters
Input Parameters
a_ID_H: Toothbrush ID code - high byte
a_ID_L：Toothbrush ID code - low byte
a_Rx_STA: a user-defined parameter for the toothbrush body
Output Parameters Null
Program Description
After this API is executed, a user-defined communication packet will be
transmitted.
Refer to the Communication Principle Description for the packet formats in detail.
The following table lists each API used by the charging base.
Command Name
Functional Description
Demodulation
Parse the communication data and confirm whether the toothbrush body ID is
consistent with the charging base ID
OCP_demo_trim
Automatically calibrate the decoding level
PWM_ping_cycle
Transmit control subroutine
time_init
Timer initialisation
OCP_CAL OCP comparator circuit offset calibration
DELAY_10us
10µs delay subroutine
The following table details each API used by the charging base.
API Name
Demodulation
API Function
Parse the communication data and confirm whether the toothbrush body ID is
consistent with the charging base ID
Input Parameters
Null
Output Parameters
user_fg_demodu_ok will be 1 when the toothbrush body ID is consistent with the
charging base ID
Program Description
After this API is executed, parse the communication data and confirm whether the
toothbrush body ID is consistent with the charging base ID. user_fg_demodu_ok
is set to 1 if the results match and 0 if not.
API Name
OCP_demo_trim
API Function Automatically calibrate the decoding level
Input Parameters Null
Output Parameters
Null
Program Description
After this API is executed, the decoding level will be automatically calibrated.
API Name
PWM_ping_cycle
API Function
Transmit control subroutine
Input Parameters
Null
Output Parameters
Null
Program Description
After this API is executed, user_fg_demodu_ok and delay time will determine
whether to continue to enable wireless charging
API Name
time_init
API Function
Timer initialisation
Input Parameters Null
Output Parameters Null
Program Description
After this API is executed, the timer for transmission control will be initialised.

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API Name OCP_CAL
API Function
OCP comparator circuit offset calibration
Input Parameters
Null
Output Parameters
Null
Program Description
After this API is executed, the OCP comparator circuit offset will be calibrated
API Name
DELAY_10µs
API Function
10µs delay subroutine
Input Parameters
ACC
Output Parameters
Null
Program Description
After this API is executed,, there is a delay of ACC×10 microseconds
Test Data
Test Item
V
IN
(V)
I
IN
(mA)
V
OUT
(V)
I
OUT
(mA)
Efficiency
Standby current
(uncharged)
Measured Data
5.1
80
5.25
45
57.9%
1µA
Conclusion
This application note has introduced how to use the BP45F0044 and BP45F1330 devices for
wireless charging toothbrushes. It has also explained the operating principle and software control
process of wireless charging toothbrushes. Based on the wireless charging toothbrush charging
management, it is shown how ID recognition is implemented and the lithium battery is charged by
the integrated linear battery charger using a constant current and constant voltage. The charging
base includes an integrated demodulation circuit, which reduces the PCB size and the number of
required peripheral components resulting in simplified product development.
Reference File
Reference file: BP45F0044 & BP45F1330 Datasheet.
For more information, consult the Holtek official website: www.holtek.com.
Revision and Modification Information
Date Author Issue
Modification Information
2021.06.08
陳振隆
V1.00
First revision

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