bq500212A

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SLUSBD6B – JULY 2013 – REVISED NOVEMBER 2013

Application Information

Coils and Matching Capacitors

The coil and matching capacitor selection for the transmitter has been established by WPC standard. These

values are fixed and cannot be changed on the transmitter side.

An up to date list of available and compatible A5 or A11 transmitter coils can be found here (Texas Instruments

Literature Number SLUA649):

Capacitor selection is critical to proper system operation. A total capacitance value of 400 nF is required in the

resonant tank. A 400-nF capacitor is not a standard value and therefore several must be combined in parallel. It

is recommended to use 4 x 100nF, as these are very commonly available.

NOTE

A total capacitance value of 400 nF/50 V is required in the resonant tank to achieve a 100-

kHz resonance frequency.

To achieve the 400nF total capacitance in the resonant tank, the bq500212A sensitive demodulation circuitry

allows the use of three (3) lower cost 100nF/X7R type capacitors in parallel with one (1) high quality 100nF/C0G

type, thereby reducing system cost from competitive solutions requiring four C0G types.

The capacitors chosen must be rated for 50 V operation. Use quality capacitors from reputable vendors such as

KEMET, MURATA or TDK.

Dynamic Power Limiting™

Dynamic Power Limiting™ (DPL) allows operation from a 5-V supply with limited current capability (such as a

USB port). When the input voltage is observed drooping, the output power is dynamically limited to reduce the

load and provides margin relative to the supply’s capability.

Anytime the DPL control loop is regulating the operating point of the transmitter, the LED will indicate that DPL is

active. The LED color and flashing pattern are determined by the LED Table. If the receiver sends a Control

Error Packet (CEP) with a negative value, (for example, to reduce power to the load), the WPTX in DPL mode

will respond to this CEP via the normal WPC control loop.

NOTE

The power limit indication depends on the LED_MODE selected.

Copyright © 2013, Texas Instruments Incorporated

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