Datasheet

bq51013B
SLUSB62A –MARCH 2013–REVISED OCTOBER 2013 www.ti.com
What this plot conveys about the operating point is that a specific load and rectifier target condition consequently
results in a specific operating frequency (for the type A1 TX). For example, at 1 A the dynamic rectifier target is
5.15 V. Therefore, the operating frequency will be between 150kHz and 160kHz in the above example. This is an
acceptable operating point. If the operating point ever falls outside the WPC frequency range (110kHz –
205kHz), the system will never converge and will become unstable.
In regards to transient analysis, there are two major points of interest:
1. Rectifier voltage at the ping frequency (175kHz).
2. Rectifier voltage droop from no load to full load at the constant operating point.
In this example, the ping voltage will be approximately 5 V. This is above the UVLO of the bq5101xB and;
therefore, startup in the WPC system can be ensured. If the voltage is near or below the UVLO at this frequency,
then startup in the WPC system may not occur.
If the max load step is 1 A, the droop in this example will be Approximately1V with a voltage at 1 A of
Approximately 5.5 V (140 kHz load-line). To analyze the droop locate the load-line that starts at 7 V at no-load.
Follow this load-line to the max load expected and take the difference between the 7V no-load voltage and the
full-load voltage at that constant frequency. Ensure that the full-load voltage at this constant frequency is above
5V. If it descends below 5V, the output of the power supply will also droop to this level. This type of transient
response analysis is necessary due to the slow feedback response of the WPC system. This simulates the step
response prior to the WPC system adjusting the operating point.
NOTE
Coupling between the primary and secondary coils will worsen with misalignment of the
secondary coil. Therefore, it is recommended to re-analyze the load-lines at multiple
misalignments to determine where, in planar space, the receiver will discontinue operation.
Recommended Rx coils can be found in Table 7:
Table 7.
Output Current
Manufacturer Part Number Dimensions Ls Ls’ Application
Range
TDK WR-483250-15M2-G 48 x 32mm 10.4 μH 12 μH
(1)
50-1000 mA General 5V Power Supply
TDK WR-383250-17M2-G 38 x 32mm 11.1 μH 12.3 μH
(1)
50-1000 mA Space limited 5V Power Supply
Vishay IWAS-4832FF-50 48 x 32mm 10.8 μH 12.5 μH
(1)
50-1000 mA General 5V Power Supply
Mingstar 312-00012 48 x 32mm 10.8 μH 12.9 μH
(1)
50-1000 mA General 5V power Supply
Mingstar 312-00015 28 x 14mm 36.5 μH 45 μH
(2)
150-1000 mA Space limited 5V Power Supply
(1) Ls’ measurements conducted with a standard battery behind the Rx coil assembly. This measurement is subject to change based on
different battery sizes, placements, and casing material.
(2) Battery not present behind the Rx coil assembly. Subject to drop in inductance depending on the placement of the battery.
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