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Test Report December 2015
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TIDA-00762 Test Report Bill Johns BMS/WLPC
Abstract The TIDA-00762 is a wireless power transmitter using
the bq50002 and bq500511 devices in a small form factor design
targeted at low power wearable devices. Input voltage to the unit
is 5V from a Micro USB connector. The low power design is
recommended for operation with receiver (load) devices at up to 1W
(5V @ 200mA).
All key transmitter circuits are laid out in a 280mm2 area (less
than 14mm x 22mm). The transmitter coil is a Wurth P/N
760308101103. PCB is 38mm X 76mm (1.5” X 3.0”).
The design is based on WPC-Qi compatible components and may
operate with many Qi compliant receivers. Due to its reduced output
power capability and smaller diameter coil it cannot be certified
to the Qi standard. For higher power applications, the TIDA-0334
reference design can be used for 2.5W output power. For 5W and 10W
applications standard bq50/51xxx EVM modules can be used.
Figure 1. TIDA-00762 Photo
Document History Version Date Author Notes
1.0 Dec 2015 Bill Johns First release
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2 TIDA-00762 Test Report
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Disclosing party under this Agreement, or any direct product of
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the state and end-use of this product or technology, and in
compliance with the export control regulations of dual-use goods in
force in the origin and exporting countries, this technology is
classified as follows: US ECCN: 3E991 EU ECCN: EAR99 And may
require export or re-export license for shipping it in compliance
with the applicable regulations of certain countries. Wireless
Power System Overview: The typical wireless power system has two
parts, the transmitter (TX) and receiver(RX). The transmitter will
converter DC input power to AC power. The AC power is transferred
through a magnetic field created by the transmitter coil to the
receiver coil. The receiver will convert the AC power back to DC
power for the load. The receiver controls the transmitter and power
transfer with a serial communications protocol sending such
information as operating point, error and additional control /
information. For more information on TI wireless power see
www.ti.com/bqTESLA.
Figure 1 Typical Wireless Power System
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TIDA-00762 Test Report 3
Adaptations from standard wireless transmitter circuits: The
TIDA-00762 solution is created by combining two low cost devices,
the Analog Front End (bq50002) and the Transmitter Controller
(bq500511). This combination is a popular choice for up to 5W, WPC
Qi-compatible wireless power designs. This wireless power
transmitter controller has the advantage of being powered from a
common +5VDC power source, such as a USB adapter. The standard
wireless power transmitter application circuit that has been
certified to meet the WPC – Qi standard is shown in the bq50002
EVM: http://www.ti.com/tool/bq50002evm-607. For smaller, more
customized designs found in wearable applications, the
Qi-compatibility requirement may be relaxed if the system can match
a specific transmitter (TX) circuit to a specific receiver (RX)
circuit. In general, wireless power system designs with very small
RX coils as used in small-form-factor products work best with
correspondingly matched smaller TX coils. See article
http://www.ti.com/lit/ml/slyt570/slyt570.pdf for further reference.
Wearable products may require a range of power levels, typically
under 2.5W total for battery charging. Products that require 2.5W
output power (e.g. charging a Li-Ion cell at approximately 500mA)
can utilize the previous reference design TIDA – 00334, which uses
a 30mm diameter coil and can fit all the electronics into the same
space (circular area with 30mm diameter). The TIDA-00762 is
intended for the smaller, lower power category of wearable devices
that require the smallest possible receiver coils in the range of
10 – 20mm diameters. The TIDA-00762 uses a very small 30mm diameter
TX coil to allow use with very small RX coils. Because of the very
small coil size, the recommended output power to the load is 1 Watt
maximum (e.g. Li-Ion battery charging at 150 ~ 200mA max) based on
typical thermal limitations. Higher power is possible but
evaluation of thermal performance in the specific application would
need to be evaluated. The TIDA-00762 will use a 30mm TX coil P/N
760308101103 from Wϋrth Elektronik this a 6.5µH coil with DCR of
0.15 Ω. Other coils with the same Inductance and DCR can be used.
For a smaller solution the 20mm TX coil P/N 760308101104 from Wϋrth
can be used. A smaller TX coil will work better with smaller RX
coils; similar size will improve coupling and efficiency. But
charging area will be reduced and alignment is more critical
possibly requiring mechanical alignment aid. Note—RX to TX coil
distance should be a min of 2.5mm and max of 5.0mm. To maintain a
min distance from TX coil to RX coil it is recommended to add a
plastic cover similar to what is used on the standard evaluation
module, bq50002EVM-607.
Compatible Receivers / Coils for testing with TIDA-00762:
bq51xxx EVMs and Reference Designs
The bq51003 wireless power receiver is optimized for low power
applications. However, the standard coil used on this EVM is
relatively large and not typically useful for small / low power
wearable applications. The TDK WR222230 (26 µH) is an example of a
smaller coil that is half the diameter of the standard EVM coil.
The combination of the bq51003 and WR222230 are an example of a
small low power receiver solution. The standard bq51003 EVM, or
alternatively other TI receiver reference designs such as
TIDA-00318 (http://www.ti.com/tool/tida-00318) can be used in
combination with the TIDA-00762 transmitter design, but the
standard coil should be replaced with the smaller coil. Care must
be taken to tune the AC1 capacitance to match any changes in coil
inductance. In general, receiver coils in the 20mm diameter range
can be used with the TIDA-00762 reference design. Smaller receiver
coils will require greater inductance values for good power
transfer.
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4 TIDA-00762 Test Report
If using a bq5105xB – based receiver circuit, the wireless
receiver can be connected directly to the Li-Ion cell and provides
direct charge control for the battery. However the charge current
should be scaled according to the power level available from the
transmitter (typically 200 – 250mA max into the cell). Because the
bq5105xB is capable of providing max charge current up to 1A, the
full range of charge current available from this receiver cannot be
achieved with the low power TIDA-00762 transmitter. Also, the
current taper control accuracy of the bq5105xB is limited, and the
bq5105xB is not recommended for charge currents < 100mA (“fast
charge”) since the taper current detection will not be accurate at
low levels (< 25mA).
The TIDA-00318 reference design uses a bq51003 low power
receiver (5V out) and a bq25100 low-current precision charger. This
allows charging and precise control of the low currents (< 250mA
with 1mA accurate taper control) used in small / wearable device
batteries.
Figure 2 Test Receiver Coil TIDA – 00318 Reference Design
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TIDA-00762 Test Report 5
Block Diagram:
Figure 3 TIDA – 00762 Block Diagram
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6 TIDA-00762 Test Report
Schematic:
Figure 4 Circuit Schematic
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TIDA-00762 Test Report 7
Configuration Options:
LED Mode – Resistors R21 & R3 control the behavior of status
LED D4, D5 and D6. The recommended value for this circuit is 100k /
24.9k Ω for control option 9.
In this mode: Standby---all LEDs are off Power Transfer---Green
LED will blink (about 1 Hz) Charge Complete---Green LED is on
Fault---Red LED is on FOD Warning---Red LED blinks fast (about 5
Hz) DPL---Red LED blinks slow (about 1 Hz) Other modes are
available see bq5000511 data sheet Table 1.
BUZZ (TP8) – Optional external buzzer connections. See bq500511
data sheet for additional information.
SDA / SCL / AGND – I2C interface to the bq500511 can be used
with software tools to monitor device operation.
Test Results:
Figure 6 shows a typical start up behavior for the TX and RX as
the RX is placed on a TX in standby. The TX can be seen
transitioning from standby to power transfer.
Figure 6 Start Up into 200mA load, Horizontal Axis 500ms/div
CH 1-TX Coil 10V / Div
CH2- RX V-RECT 2V / Div
CH3 - V-OUT 2.0V / Div
1 - VRECT at ping is 6V well above UVLO
2 - SS / ID / Config packet 3 - RX tune TX to operating point
about 7V
4 - Output 5V Enable
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8 TIDA-00762 Test Report
Figure 7 shows the TX and RX behavior during Charge Complete,
EPT 01. The bq51003 is configured to send EPT 01 constantly (EN1 /
2 high). In response TX will end power transfer and send analog
ping every 500ms and digital ping every 5.2us.
Figure 7 Charge Complete, End Power Transfer 01, Horizontal Axis
1000ms/div
CH4-TX Input Current 200mA / Div
CH3–V-OUT 2.0V / Div
CH2-RX V-RECT 2.0V / Div
CH1-TX Coil 5V / Div
Digital Ping
Analog Ping
Charge Complete—RX sent EPT01 --TX sends digital ping every 5
seconds --TX sends analog ping every 500ms --The TIDA-00762 input
current about 50mA
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TIDA-00762 Test Report 9
Figure 8 shows the TX and RX behavior during Standby with no RX
on the TX charging pad. TX will use a low power analog ping to
check for the RX then send digital ping. The digital ping is higher
power and can power a receiver. Analog ping is sent every 500ms and
digital ping every 5 seconds.
Figure 8 Standby – No RX on TX, Horizontal Axis 200ms/div
Figure 9 shows the efficiency across the power range with the
bq51003EVM-764 with TDK coil WR222230. This is the total system
efficiency including the transmitter, coils and receiver. Note
recommended output power is 1W.
Figure 9 TIDA-00762 Efficiency with bq51003
0%10%20%30%40%50%60%70%80%90%
100%
0 500 1000 1500 2000 2500
Efficiency
Output Power (W)
CH4-TX Input Current 200mA / Div
Standby Mode—No RX --TX sends digital ping every 5 seconds --TX
will send analog ping every 500ms --If RX is present it will
reply
Digital Ping every 5000ms
Input current 50mA and 0mA between pulses
CH1-TX Coil 5V / Div
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10 TIDA-00762 Test Report
FOD Protection:
This circuit does have Foreign Object Protection (FOD) for
detection of metal objects between the RX and TX during charging.
FOD can be disabled by connecting FOD_THR to 3V.
FOD_THR is set by R23 and R15. This will set the point where FOD
declares a fault.
FOD_CAL is set by R22 and R5. This will adjust the slope of the
loss curve.
See data sheet for additional information on FOD.
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TIDA-00762 Test Report 11
Thermal Measurements
The following figure shows a thermal image of the TIDA-00762
operating with the bq51003EVM-764 RX at 250mA output load, 1.25W.
Note recommended output power is 1W but 1.25W is shown to
demonstrate design margin.
Figure 10 TIDA-00762, RX output current 250mA
References 1. Data Sheet bq50002 Wireless Power Transmitter
Analog Front End for WPC (SLUSBW1A) 2. Data Sheet bq500511 Wireless
Power Transmitter Controller for WPC (SLUSCD3A) 3. Data Sheet
bq51003 Wireless Power Receiver for WPC (SLUSBC8) 4. User Guide
bq51003 Wireless Power Receiver (SLUUAU8) 5. TI Designs TIDA-00318
Wireless Charger for Lower Power Wearable Applications
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