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RT1650 Application Note



I2C

The RT1650 provides I2C interface to communicate with external host device. Besides OTP firmware programming and MTP setting programming can be approached through the I2C interface, the external host can also communicate with the RT1650 to achieve more flexible applications. For example, the host can read the ADC information via the I2C Interface. The example code please refer to the annex A. Table 1 shows the specification of the I2C. Table 2 shows the RT1650 register definition. In addition, the I2C is used to read the internal status and the power source is from the VRECT. If the wireless function disable or in the adapter mode, the I2C can’t be accessed.

 

  • I2C Slave

0100010X (in binary format)

0x44 / 0x45 (hex format, include R/W bit)

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Table 1. RT1650 I2C specification

Symbol

Description

Min

Typ

Max

Unit

VIL_I2C

I2C Input logic low

0.6

V

VIH_I2C

I2C Input logic high

1.2

V

fSCL

SCL frequency

10

400

kHz


Table 2. RT1650 register definition

Address

MSB

LSB

Name

Description

0x64

7

0

Vrect

Vrect (4V~8V), unit = 15.68mV

0x66

7

0

Vout

Vout (3V~6V), unit = 11.76mV

0x67

7

0

Iout

Iout (0A~2A), unit = 7.84mA

0x78

7

0

last CE packet

last CE packet

0x79

7

0

last RP packet

last RP packet

0x7A

7

0

Received Power [7:0] (mW)

low byte of Received Power (mW)

0x7B

6

0

Received Power [14:8] (mW)

high byte of Received Power (mW)

0x7B

7

7

Received Power updating flag

0 : Received Power is valid
1 : Received Power is updating, not valid

0x10

7

7

Vout enable

0 : Vout is disable
1 : Vout is enable

0x02

7

0

freq_cnt [7:0]

Frequency = 1000 / ( (freq_cnt[13:0] * 0.11) / 128) kHz

0x03

5

0

freq_cnt [13:8]

0x7C

3

0

WPC phase status

WPC status
0 : booting
1 : ping phase
2 : ID_CF phase
3 : Negotiation phase
4 : power transfer phase

e.g. : 1. If read the 0x7A data is 0xAA, 0x7B data is 0x21.

The received power is 0x21 * 256 + 0xAA = 8618mW.

2. If read the 0x7A data is 0x55, 0x7B data is 0x91.

This data should be ignore because the data is updating.

RT1650 will update the ADC status of the VRECT, Vout and Iout before each CE packet and calculate the received power then updating the register before each RP packet. The time interval of each CE packet is 150ms and each RP packet is 1500ms. The time of the data updating is only few micro seconds. By the way, the RP function is using to detect the FOD for steady state.

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Figure 1. Power Receiver timing in the power transfer phase


Table 3. Power Receiver timing in the power transfer phase

Parameter

Symbol

Minimum

Target

Maximum

Unit

Interval*

tinterval

250

350.0+0

ms

Controller time

tcontrol

24.0-0

25

N.A.

ms

Received Power Packet time

treceived

1500

4000.0

ms


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Figure 2. Received Power Calculate timing



Power Transfer phases

Figure 3. shows the 4 power transfer phases for the WPC v1.1.

  • SELECTION : As soon as the Power Transmitter applies a Power Signal, the Power Receiver shall enter the selection phase.
  • PING : The power Receiver should send the Digital Ping Packet to power Transmitter then into next phase. If not, the system shall revert to the Selection phase. The power Receiver also can send the End Power transfer Packet to stop the power Transmitter.
  • IDENTIFICATION & CONFIGURATIOIN : In this phase, the Power Receiver identifies the revision of the System Description Wireless Power Transfer the Power Receiver complies and configuration information such as the maximum power that the Power Receiver intends to provide at its output. The Power Transmitter uses this information to create a Power Transfer Contract.
  • POWER TRANSFER : In this phase, the Power Transmitter continues to provide power to the Power Receiver. The power Receiver sends the Control Error Packet for adjusting the Primary Cell current. The Power Transmitter stops to provide power when the Received Power Packet is too low to trigger the FOD function or End Power Transfer Packet is sent from power Receiver.

 

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Figure 3. WPC v1.1 Low Power Transfer Phases



Mode Selection

The RT1650 provides 2 input pins for operating mode control. The VIH of the Mode0 and Mode1 is 1.2V (min), VIL is 0.6V (max), shown as Table 4. Table 5 shows an example of operating mode control for wireless power and external adapter power. In default mode, both MODE0 and MODE1 are low, the wireless power is enabled and the adapter power has a higher priority. The wireless power is the normally operation, shown as Figure 4. Once the adapter power is detected, the wireless power will be turned off and the ADEN will be pulled low to turn on the external switch for connecting the adapter power to system load, shown as Figure 5. When the MODE1 is pulled to high, the adapter power will be turned off by the external switch and enters wireless mode to allow wireless power operation only, shown as Figure 6. In adapter mode, the wireless power is turned off always and ADEN is pulled low to turn on external switch for adapter power, shown as Figure 7. In this mode, it allows an external charger operating in USB OTG mode to connect the OUT pin to power the USB at ADD pin, shown as Figure 8. If both MODE0 and MODE1 pins are pulled to high, the wireless power and adapter power are disabled, shown as Figure 9.

Table 4. RT1650 Mode0 and Mode1 specification

Symbol

Description

Min

Typ

Max

Unit

VIL_Mode

Mode Input logic low

0.6

V

VIH_Mode

Mode Input logic high

1.2

V


Table 5. Operation Mode Control

Mode

MODE0

MODE1

Wireless Power

Adapter Power

OTG

Default

0

0

ON

ON(*)

OFF

Wireless

0

1

ON

OFF

OFF

Adapter

1

0

OFF

ON

Allowed

Disable

1

1

OFF

OFF

OFF

(*)Note : If both adapter power and wireless power are present, adapter power is given higher priority.


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Figure 4. Default Mode Wireless Power operation


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Figure 5. Default Mode adapter power priority operation


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Figure 6. Wireless Power Mode operation


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Figure 7. Adapter Mode operation


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Figure 8. OTG Mode operation


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Figure 9. Disable Mode operation



Thermal Management

The RT1650 provides an external device thermal management function with an external NTC thermistor and a resistor connected between TS pin and GND pin shown as Figure 10. User can use this function to control the temperature of the coil, battery or other device. An internal current source (60µA) is provided to the external NTC thermistor and generates a voltage at the TS pin. The TS voltage is detected and sent to the ADC converter for external device thermal manage control.

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Figure 10. NTC Circuit for Device Temperature Detection and Thermoregulation

The thermal management function is shown as Figure 11. If the temperature is higher than Hot_temp or lower than Cold_temp threshold, the RT1650 will send the EPT to disable the power transfer. When the detected temperature increases and reaches the desired Regulation_temp, RT1650 will decrease the current limit to reduce the output current to regulate the temperature. When the detected temperature is lower than the Regulation_temp, the current limit will increase to the default value. This function is shown as Figure 12.

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Figure 11. Thermal management function


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Figure 12. Thermoregulation Control

The thermal management is programmable by MTP of each temperature setting. Figure 13 is the Control Panel of this function. Please refer to the following description for these item.

  • Thermal Regulation check box : enable or disable all the thermal management function.
  • send EPT when HOT : Send the EPT to Tx when the temperature is higher than Hot_temp.
  • send EPT when COLD : Send the EPT to Tx when the temperature is lower than Cold_temp.
  • Regulation : Setting for the Regulation_temp (range is 0°C~155°C, step is 1°C)
  • Hot : Setting for the Hot_temp (range is 0°C~155°C, step is 1°C)
  • Cold : Setting for the Cold_temp (range is -40°C~155°C, step is 1°C)
  • Step : The current limit reducing and rising step. The unit is 0.01mA/CE. The CE interval time is 150ms as default. e.g. If the value is 40, step is 40 x 0.01mA/CE = 0.4mA/CE.
  • min current limit during : The minimum value of the thermoregulation. This value should be higher than 250mA.

 

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Figure 13. Thermal Regulation Control Panel

The NTC thermistor should be placed as close as possible to the device such as battery or mobile device. The recommended NTC thermistor is NCP15WF104F03RC (tolerance±1%, β = 4250K). The typical resistance of the NTC is 100kΩ at 25degree. The recommended resistance for R1 is 33kΩ (±1%).

The value of the NTC thermistor at the desired temperature can be estimated by the following equation.

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where TReg is the desired regulation temperature in degree Kelvin. RO is the nominal resistance at temperature T0 and β is the temperature coefficient of the NTC thermistor. Reg is the equivalent resistor of NTC thermistor in parallel with R1.

Figure 14 shows the equivalent resistance of the thermistor in parallel with R1 resistor varies with operating temperature. Figure 15 shows the VTS voltage with operating temperature. Customer can select the desire temperature and calculate the mapping data by the following equation.

Data = (VTS / 2) * 1024

If the thermal management function is not used (RNTC = open), the resistor R1 = 24kΩ must be connected between the TS and GND pins.

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Figure 14. Equivalent Resistance for Temperature Sensing


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Figure 15. Thermal Sensing Voltage



GPIO

The RT1650 provides a programmable general purpose input/output (GPIO) pin. The GPIO can be used as an input or used as a status indicator for different application. Before use this GPIO, user should discuss its functions with RICHTEK and then RICHTEK code its function into firmware.

  • GPIO can be programmed as an output port, be a status indicator. For example,
  • To control LED flashing when Rx position search
  • To indicate thermal regulation is active
  • To indicate battery is full or charging is complete
  • GPIO can be programmed as input port, to connect external signal and inform MCU. For example,
  • if GPIO is high, MCU turn on Vout
  • If GPIO is low, MCU turn off Vout
  • Option for GPIO
  • internal pull-up option (pull-up to 3.3V)
  • Internal pull-low option
  • GPIO can be push-pull or open-drain architecture when GPIO programmed as an output.

 

Table 6. RT1650 GPIO specification

Symbol

Description

min

typ

max

Vil

input logic low voltage

0.8V

Vih

input logic high voltage

2V

Vol

output low voltage

0.4V

Voh

output high voltage when push-pull architecture

2.6V

3.3V

Voh

output high voltage when open-drain architecture

Hi-Z


Table 7. RT1650 GPIO functions

Description

H

L

Output

I2C Status

Ready

Not ready

Output

Vout Status

On

Off

Output

Thermal Regulation Status

Active

Not active

Output

Battery Charge Complete Status

Active

Not active

Input

Vout Control

On

Off

Input

EPT Control (internal pull-high)

Normal operation

Send EPT



Received Power

The RT1650 is a WPC 1.1.1 compatible device. In order to enable a power transmitter to monitor the power loss across the interface as one of the possible methods to limit the temperature rise of foreign objects, the RT1650 reports its received power to the power transmitter. The received power equals the power that is available from the output of the power receiver plus any power that is lost in producing that output power (the power loss in the secondary coil and series resonant capacitor, the power loss in the shielding of the power receiver, the power loss in the rectifier). In WPC 1.1.1 specification, foreign object detection (FOD) is enforced. This means the RT1650 will send received power information with known accuracy to the transmitter. The received power is sensed as the Figure 16.

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Figure 16. Received Power Sensed

The received power can calculate by the following formula.

PRX,AC = (VRECT x IOUT) / EffRECT + Pres_loss + Poffset

     PRX, AC is the Received Power for RP packet

     VRECT is the output voltage of rectifier from ADC

     IOUT is the output current from ADC

     Eff_RECT is the efficiency of rectifier

     Poffset is the initial power offset for PTX and PRX

Pres_loss = k (RS + RESR) x IOUT2

     k is a constant coefficient

     RS is the AC resistance of Rx coil

     RESR is the AC resistance of series capacitor

RS = RX100 [1 + A (f / 100 - 1) + B (f / 100 - 1)2]

      RX100 is the Rx coil resistance at 100kHz

      F is the AC frequency from Tx

      A and B is the resistance matching coefficient

RESR = RCS100 / (f / 100)

     RCS100 is the capacitor resistance at 100kHz

To use the GUI for the FOD calibration, the customer should measure the resistance of the coil from 100kHz to 200kHz and select the RX100, coefficient A and B to match the resister with frequency. The resister of the capacitor, RCS100, could be measure or get from the datasheet. If the customer can get the WPC certification transmitter, the Poffset can be selected for initial calibration. E.g. For this coil, we can get the A = 0.56, B = 0.32, Rx100 = 362mΩ, shown as Figure 17. RCS_100 = 150mΩ. Poffset = 100mW. Then use the GUI to set the parameter to MTP, shown as Figure 19. Please refer to the following description for these item.

  • CoeffA : The coefficient A of the coil resistance matching. (range is 0~2.55, step is 0.01)
  • CoeffB : The coefficient B of the coil resistance matching. (range is 0~2.55, step is 0.01)
  • Rx100 : The resistance of the coil at 100kHz. (range is 0~510mΩ, step is 2mΩ)
  • Rcs100 : The resistance of the Cs cap at 100kHz. (range is 0~255mΩ, step is 1mΩ)
  • Power_offset : To compensate the power offset of the Tx and Rx. (range is 0~1.27W, step is 0.01W)

    

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             Figure 17. Coil resistance matching

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          Figure 18. Capacitor resistance matching


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Figure 19. Received Power Control Panel



Foreign Object Detection

For the WPC 1.1.1 standard, a Power Receiver shall report its Received Power Preceived in a Received Power Packet such that Preceived – 250mW ≤ PPR ≤ Preceived. This means that the reported Received Power should higher than the actual Received Power PPR, by at most 250mW. RT1650 provide the rectifier efficiency and the resonant tank loss compensating to minimum the power offset between the transmitter and receiver and provide the power offset for FOD function. Figure 20 is the RT1650 FOD tuning flow. For the new model, customer should measure the parameter of the Rx100, CoeffA, CoeffB and RCS100 then setting to the MTP. First step is that measure the PRx and PRxtarget by the FOD test jig, shown as Figure 21. This step can observe the power offset of the initial state and the received power behavior. The second step that we should adjust the power offset to keep the 0≤ PRX-PTX ≤ 250mW at no load, shown as Figure 22. The third step is that check the power offset for heavy load and adjust Rx100 to minimize the power difference at heavy load, shown as Figure 23. The fourth step is that check the received power again. If there is any over spec, we can modify the rectifier efficiency to optimize the power, shown as Figure 24.

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Figure 20. FOD Tuning Flow


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Figure 21. The First Step of FOD Tuning Flow


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Figure 22. The Second Step of FOD Tuning Flow


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Figure 23. The Third Step of FOD Tuning Flow


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Figure 24. The Fourth Step of FOD Tuning Flow



Battery Charge Complete Detection

The RT1650 supports battery charge complete detection function, shown as Figure 25. A programmable charge complete current threshold and a programmable charge complete detect time are provided. This function can be used to send the Charge Status packet to the transmitter for indicating a full charged status 100%. There are 3 operation modes when the charge complete status is detected, shown as Figure 26. Mode1 is to send a CS packet to transmitter only. In the Mode2, the RT1650 will send a CS packet and an EPT packet to transmitter. In the Mode3, the RT1650 will send a CS packet (0x05) then stop communication with the transmitter.

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Figure 25. The Fourth Step of FOD Tuning Flow


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Figure 26. The Fourth Step of FOD Tuning Flow

The Charge Complete is programmable by MTP of each temperature setting. Figure 27 is the Control Panel of this function. Please refer to the following description for these item.

  • enable Charge Complete : enable or disable the Battery Charge Complete Detection function.
  • Complete mA : The Charge Complete detect threshold current. (range is 0~510mA, step is 2mA)
  • Complete sec : The Charge Complete detect threshold current. (range is 0~3825sec, step is 15sec)
  • send Charge Status 100 when charge complete : Send the CS packet when Charge Complete. Enable this function for Mode1, Mode2 and Mode3.
  • send EPT when charge complete : Send the EPT packet after CS packet. Enable this function for Mode2.
  • stop packet after charge complete : Stop the communication after CS packet. Enable this function for Mode3.

 

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Figure 27. The Fourth Step of FOD Tuning Flow



MTP Program

For the MTP program, please contact to the RICHTEK to get the GUI, test Jig and the driver. The standard program step is as following description.

1. Disable the Tx or remove the coil of the Rx from Tx.

2. Supply 7V and 30mA source ability at least to the RECT pin to GND.

3. Connect the SDA, SCL and GND pins of the test jig ”RT Bridgeboard” to PCB. The customer should install the driver “RTBridgeboardUtilitiesV130.exe” first.

4. Open the “RT1650_GUI_tool”

5. Fill in the parameter.

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Figure 28. Power source at MTP program



Component Maximum Voltage Rating

The component value and the maximum voltage rating is as following suggestion, shown as Figure 29. These value is selected based on the WPC standard transmitter and 5V adapter application. The customer should be modify by the customer design and application.

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Figure 29. Application Circuit component value


Item

Part Reference

Value

Part Number

1

C1

47nF/50V/0805

GRM21B7U1H473JA01L_MURATA

2

C2

1.8nF/50V/0603/X7R

0603B182K500_WALSIN

3

CCLAMP1, CCLAMP2

0.47µF/50V/0603/X7R

C1608X7R1H474KT_TDK

4

CCOMM1, CCOMM2

22nF/50V/0603/X7R

0603B223K500_WALSIN

5

CBOOT1, CBOOT2

10nF/50V/0603/X7R

0603B103K500_WALSIN

6

CVDD1, CVDD2

1µF/10V/1005/X5R

C1005X5R1A105K050BB_TDK

7

C3

10µF/16V/0805/X5R

C2012X5R1C106KT_TDK

8

C4

1µF/10V/1005/X5R

C1005X5R1A105K050BB_TDK

0.1µF/10V/0603/X5R

C0603X5R1A104K030BC_TDK

9

C5

1µF/10V/1005/X5R

C1005X5R1A105K050BB_TDK

0.1µF/10V/0603/X5R

C0603X5R1A104K030BC_TDK

C1~C4 can use the normal X7R to replace. Part Number : 0603B473K500_WALSIN



Programmable Dynamic Rectifier Voltage Control

The RT1650 provides a programmable Dynamic Rectifier Voltage Control function to optimize the transient response and power efficiency for applications. Figure 30 show an example to summarize how the rectifier behavior is dynamically adjusted based the VRECT_SET1~4 and IOUT_TH1~3, which are available to be programmed by MTP. The RT1650 has the VRECT tracking function for the higher efficiency application, shown as Figure 31. This function use the Iout to calculate the minimum drop-out voltage of the LDO to improve the system efficiency. This function also can tracking the rectifier voltage by the VOUT when current limit. To avoid the VOUT be clamped by the VRECT when the current limit released, RT1650 provide the tracking threshold parameter for the tracking function working.

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Figure 30. Dynamic Rectifier Voltage Control


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Figure 31. VRECT Tracking control


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Figure 32. VRECT Tracking control Panel

The Dynamic Rectifier Voltage Control is programmable by MTP. Figure 32 is the Control Panel of this function. Please refer to the following description for these item.

  • VREct_1 : The rectifier voltage target of Iout < Iout_th1. (range is 5V~10V, step is 0.01V)
  • Vrect_2 : The rectifier voltage target of Iout_th1 < Iout < Iout_th2. (range is 5V~10V, step is 0.01V)
  • Vrect_3 : The rectifier voltage target of Iout_th2 < Iout < Iout_th3. (range is 5V~10V, step is 0.01V)
  • Vrect_4 : The rectifier voltage target of Iout > Iout_th3. (range is 5V~10V, step is 0.01V)
  • Iout_th1 : The threshold for the rectifier voltage change. (range is 0A~1A, step is 0.01A)
  • Iout_th2 : The threshold for the rectifier voltage change. (range is 0A~1A, step is 0.01A)
  • Iout_th3 : The threshold for the rectifier voltage change. (range is 0A~1A, step is 0.01A)
  • Iout_th_hys : The hysteresis of the Dynamic Rectifier Voltage Control. (range is 0A~1A, step is 0.01A)
  • enable Vrect Tracking : Enable Vrect Tracking function. Set the Vrect_4_Tr = Vout + Iout * R + Voffset.
  • R : The equivalent resistor of the Vrect Tracking function. (range is 0~1.275Ω, step is 5mΩ)
  • Voffset : The offset voltage of the Vrect Tracking function. (range is 0~2.55V, step is 0.010V)

 

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Figure 33. Iout limit control Panel

The Iout limit Control is programmable by MTP. Figure 33 is the Iout limit Control Panel. Please refer to the following description for this item.

  • Limit : The Iout limit threshold. (range is 200mA~1800mA, step is 10mA)



Vout disable for battery system

RT1650 have a detect function for loading is battery to avoid the reset fail. This function detects the Tx power then check the VRECT and VOUT status. If the Tx have no power, RT1650 will close the VOUT and VRECT.



Position Search

RT1650 provide the position search function for customer. This function adjusts the CHG pin frequency to control the LED flicker to let the user can know the best position for coupling. For this function:

1. Enable this function in MTP.

2. A LED and a 10kΩ resistor should be connected to the RECT pin and CHG pin.



CE packet interval

The communication of the WPC is the ASK modulation and the bit encoding scheme. If the check sum data send from Rx is different with the check sum value, Tx will ignore this packet. If the Tx can’t receive the complete packet in 1500ms, Tx will time-out and shut down. For the real system, the load may changes in the communication and that may let the data wrong. RT1650 provide the CE interval control function. If the Iout change more than the threshold setting after the communication, RT1650 reduce the packet interval time to avoid the check sum error then time out.



Annex A

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