BQ500412 Datasheet, PDF (17/28 Pages) Texas Instruments – Low System Cost, Wireless Power Controller for WPC TX A6

bq500412
www.ti.com
SLUSBO2A – NOVEMBER 2013 – REVISED DECEMBER 2013
Trickle Charge and CS100
The WPC specification provides an End-of-Power Transfer message (EPT–01) to indicate charge complete.
Upon receipt of the charge complete message, the bq500412 will change the LED indication. The exact
indication depends on the LED_MODE chosen.
In some battery charging applications there is a benefit to continue the charging process in trickle-charge mode
to top off the battery. There are several information packets in the WPC specification related to the levels of
battery charge (Charge Status). The bq500412 uses these commands to enable top-off charging. The bq500412
changes the LED indication to reflect charge complete when a Charge Status message is 100% received, but
unlike the response to an EPT, it will not halt power transfer while the LED is solid green. The mobile device can
use a CS100 packet to enable trickle charge mode.
If the reported charge status drops below 90% normal, charging indication will be resumed.
Current Monitoring Requirements
The bq500412 is WPC1.1 ready. In order to enable the FOD or PMOD features, current monitoring circuitry must
be provided in the application design.
For proper scaling of the current monitor signal, the current sense resistor should be 20 mΩ and the current
shunt amplifier should have a gain of 50, such as the INA199A1. For FOD accuracy, the current sense resistor
must be a quality component with 1% tolerance, at least 1/4-Watt rating, and a temperature stability of ±200
PPM. Proper current sensing techniques in the application hardware should also be observed.
If WPC compliance is not required current monitoring can be omitted. Connect the I_SENSE pin (pin 42) to GND.
All Unused Pins
All unused pins can be left open unless otherwise indicated. Pin 4 can be tied to GND and flooded with copper to
improve ground shielding. Please refer to the pin definition table for further explanations.
Design Checklist for WPC1.1 Compliance with the bq500412
• Coil and capacitor selection matches the A6 specification.
• Total 147-nF center and 133-nF side coil resonant capacitor requirement is met.
• Precision current sense amp used, such as the INA199A1. This is required for accurate FOD operation.
• Current shunt resistor 1% and <200 PPM. This is required for accurate FOD operation.
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