BQ500412 Datasheet, PDF (16/28 Pages) Texas Instruments – Low System Cost, Wireless Power Controller for WPC TX A6

bq500412
SLUSBO2A – NOVEMBER 2013 – REVISED DECEMBER 2013
www.ti.com
Fault Handling and Indication
The following table provides approximate durations for the time before a retry is attempted for End Power
Transfer (EPT) packets and fault events. Precise timing may be affected by external components, or may be
shortened by receiver removal. The LED mode selected determines how the LED indicates the condition or fault.
CONDITION
EPT-00
EPT-01
EPT-02
EPT-03
EPT-04
EPT-05
EPT-06
EPT-07
EPT-08
OC (over current)
NTC (external sensor)
PMOD/FOD warning
PMOD/FOD
Power Transfer Start Signal
DURATION
(before retry)
Immediate
5 seconds
5 seconds
5 minutes
Immediate Over
Immediate Over
5 seconds
Not applicable
Immediate
1 minute
5 minutes
12 seconds
5 minutes
HANDLING
Unknown
Charge complete
Internal fault
temperature
voltage
current
failure
Reconfiguration
No response
10 seconds LED only,
2 seconds LED +
buzzer
The bq500412 features two signal outputs to indicate that power transfer has begun. Pin 23 outputs a 400-ms
duration, 4-kHz square wave for driving low cost AC type ceramic buzzers. Pin 24 outputs logic high, also for 400
ms, which is suitable for DC type buzzers with built-in tone generators, or as a trigger for any type of customized
indication scheme. If not used, these pins can be left open.
Power-On Reset
The bq500412 has an integrated Power-On Reset (POR) circuit which monitors the supply voltage and handles
the correct device startup sequence. Additional supply voltage supervisor or reset circuits are not needed.
External Reset, RESET Pin
The bq500412 can be forced into a reset state by an external circuit connected to the RESET pin. A logic low
voltage on this pin holds the device in reset. For normal operation, this pin is pulled up to 3.3 V_CC with a 10-kΩ
pull-up resistor.
Low Power Mode, SNOOZE
During standby, when nothing is on the transmitter pad, the bq500412 pings the surrounding environment at
fixed intervals. The ping interval can be adjusted; the component values selected for the SNOOZE circuit
determine this interval between pings. Time for SNOOZE is set by an RC time constant controlling the Enable of
a 3.3V LDO. The LDO will remove 3.3V from the bq500412 to reduce power. The choice of the ping interval
effects two quantities: the idle efficiency of the system, and the time required to detect the presence of a receiver
when it is placed on the pad. A trade off should be made which balances low power (longest ping interval) with
good user experience (quick detection through short ping interval) while still meeting the WPC requirement for
detection within 0.5 seconds. Typical RC time constant values for the SNOOZE circuit are 392k ohms and 4.7uF.
The value can be adjusted to increase or decrease the ping interval.
The system power consumption is approximately 300 mW during an active ping of all three coils, which lasts
approximately 210 ms, and 40 mW for the balance of the cycle. A weighted average can thus be used to
estimate the overall system’s idle consumption:
If T_ping is the interval between pings in ms, P_idle in mW is approximately:
(40 x (T_ping – 210) + 300 x 210)/T_ping
(2)
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