BQ51013A Datasheet, PDF (28/45 Pages) Texas Instruments – INTEGRATED WIRELESS POWER SUPPLY RECEIVER

bq51013A
bq51014
SLUSAY6A – MARCH 2012 – REVISED JUNE 2012
www.ti.com
Adaptive Communication Limit
The Qi communication channel is established via backscatter modulation as described in the previous sections.
This type of modulation takes advantage of the loosely coupled inductor relationship between the Rx and Tx coil.
Essentially the switching in-and-out of the communication capacitor or resistor adds a transient load to the Rx
coil in order to modulate the Tx coil voltage/current waveform (amplitude modulation). The consequence of this
technique is that a load transient (load current noise) from the mobile device has the same signature. In order to
provide noise immunity to the communication channel, the output load transients must be isolated from the Rx
coil. The proprietary feature Adaptive Communication Limit achieves this by dynamically adjusting the current
limit of the regulator. When the regulator is put in current limit, any load transients will be offloaded to the battery
in the system.
Note that this requires the battery charger IC to have input voltage regulation (weak adapter mode). The output
of the Rx appears as a weak supply if a transient occurs above the current limit of the regulator.
The Adaptive Communication Limit feature has two current limit modes and is detailed in the table below:
I_OUT
< 300 mA
> 300 mA
Table 5.
Communication Current Limit
Fixed 400 mA
I_OUT + 50 mA
The first mode is illustrated in Figure 25. In this plot, an output load pulse of 300 mA is periodically introduced on
a DC current level of 200 mA. Therefore, the 400 mA current limit is enabled. The pulses on V_RECT indicate that a
communication packet event is occurring. When the output load pulse occurs, the regulator limits the pulse to a
constant 400 mA and; therefore, preserves communication. Note that V_OUT drops to 4.5 V instead of GND. A
charger IC with an input voltage regulation set to 4.5 V allows this to occur by offloading the load transient
support to the mobile device’s battery
The second mode is illustrated in Figure 26. In this plot, an output pulse of 200 mA is periodically introduced on a
DC current level of 400 mA. Therefore, the tracking current mode (I_OUT + 50 mA) is enabled. In this mode the
bq5101x measures the active output current and sets the regulators current limit 50 mA above this
measurement. When the load pulse occurs during a communication packet event, the output current is regulated
to 450 mA. As the communication packet event has finished the output load is allowed to increase. Note that
during the time the regulator is in current limit V_OUT is reduced to 4.5 V and 5 V when not in current limit.
Synchronous Rectification
The bq5101x provides an integrated, self-driven synchronous rectifier that enables high-efficiency AC to DC
power conversion. The rectifier consists of an all NMOS H-Bridge driver where the backgates of the diodes are
configured to be the rectifier when the synchronous rectifier is disabled. During the initial startup of the WPC
system the synchronous rectifier is not enabled. At this operating point, the DC rectifier voltage is provided by the
diode rectifier. Once V_RECT is greater than UVLO, half synchronous mode will be enabled until the load current
surpasses 120 mA. Above 120 mA the full synchronous rectifier stays enabled until the load current drops back
below 100 mA where half synchronous mode is enabled instead.
Temperature Sense Resistor Network (TS)
bq5101x includes a ratiometric external temperature sense function. The temperature sense function has two
ratiometric thresholds which represent a hot and cold condition. An external temperature sensor is recommended
in order to provide safe operating conditions for the receiver product. This pin is best used for monitoring the
surface that can be exposed to the end user (e.g. place the NTC resistor closest to the user).
Figure 41 allows for any NTC resistor to be used with the given V_HOT and V_COLD thresholds.
28
Submit Documentation Feedback
Product Folder Link(s): bq51013A bq51014
Copyright © 2012, Texas Instruments Incorporated