BQ500211A Datasheet, PDF (17/27 Pages) Texas Instruments – 5-V, WPC1.1 Compliant Wireless Power Transmitter Manager

bq500211A
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APPLICATION INFORMATION
SLUSBB1 – DECEMBER 2012
Overview
The application schematic for the transmitter with reduced standby power is shown in Figure 7.
CAUTION
Please check the bq500211A product page for the most up-to-date application
schematic and list of materials package before starting a new design.
Input Regulator
The bq500211A requires 3.3 VDC to operate. A buck regulator or a linear regulator can be used to step down
from the 5-V system input. Either choice is fully WPC compatible, the decision lies in the user's requirements with
respect to cost or efficiency.
For highest efficiency use a low-cost buck regulator, TPS62237, which on account of a 3-MHz switching
frequency, can use a 0805 size chip inductor. This results in a very attractive combination, high performance,
small size, ease of use and low cost.
Power Train
The bq500211A drives a phase-shifted full bridge. This is essentially twin half bridges and the choice of driver
devices is quite simple, a pair of TPS28225 synchronous MOSFET drivers are used with four CSD17308Q2
NexFETs. Other combinations work and system performance with regards to efficiency and EMI emissions vary.
Any alternate MOSFETs chosen must be fully saturated at 5-V gate drive and be sure to pay attention whether or
not to use gate resistors; some tuning might be required.
Low Power Supervisor
Power reduction is achieved by periodically disabling the bq500211A while LED and housekeeping control
functions are continued by U4 – the low-cost, low quiescent current microcontroller MSP430G2001. When U4 is
present in the circuit (which is set by a pull-up resistor on bq500211A pin 25), the bq500211A at first power-up
boots the MSP430G2001 with the necessary firmware and the two chips operate in tandem. During standby
operation, the bq500211A periodically issues a SLEEP command, Q12 pulls the RESET pin low, therefore
reducing its power consumption. Meanwhile, the MSP430G2001 maintains the LED indication and stores
previous charge state during this bq500211A reset period. This bq500211A reset period is set by the RC time
constant network of R26, C22 (see Figure 7). WPC compliance mandates receive detection within 500 ms, the
power transmitter controller, bq500211A, awakes every 400 ms to produce an analog ping and check if a valid
device is present. Increasing this time constant, therefore is not advised; shortening could result in faster
detection time with some decrease in efficiency.
Disabling Low Power Supervisor Mode
For lowest cost or if the low-power supervisor is not needed, please refer to Figure 8 for the application
schematic.
NOTE
Current sense shunt and amplifier circuitry are optional. The circuitry is needed to enable
Foreign Object Detection (FOD) and a forward migration path to WPC1.1 compliance.
Copyright © 2012, Texas Instruments Incorporated
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