Datasheet

COMM1 COMM2
RECTIFIER
24W 24W
COMM_DRIVE
bq51011
bq51013
SLVSAT9D –APRIL 2011–REVISED AUGUST 2012 www.ti.com
Communication
bq5101x provides two identical, integrated communication FETs which are connected to the pins COMM1 and
COMM2. These FETs are used for modulating the secondary load current which allows bq5101x to communicate
error control and configuration information to the transmitter. Figure 25 below shows how the COMM pins can be
used for resistive load modulation. Each COMM pin can handle at most a 24Ω communication resistor.
Therefore, if a COMM resistor between 12Ω and 24Ω is required COM1 and COM2 pins must be connected in
parallel. bq5101x does not support a COMM resistor less than 12Ω.
Figure 25. Resistive Load Modulation
In addition to resistive load modulation, the bq5101x is also capable of capacitive load modulation as shown in
Figure 26 below. In this case, a capacitor is connected from COMM1 to AC1 and from COMM2 to AC2. When
the COMM switches are closed there is effectively a 22nF capacitor connected between AC1 and AC2.
Connecting a capacitor in between AC1 and AC2 modulates the impedance seen by the coil, which will be
reflected in the primary as a change in current.
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