Datasheet

ILIM
MAX
ILIM
MAX
ILIM
ILIM
1
262
R
I
314
I 1 2 I
R
R R 188
=
= ´ =
= +
.
( )
DIS RECT OUT OUT
P = V - V × I
bq51013B
SLUSB62A –MARCH 2013–REVISED OCTOBER 2013 www.ti.com
Dynamic Efficiency Scaling
The Dynamic Efficiency Scaling feature allows for the loss characteristics of the bq5101xB to be scaled based on
the maximum expected output power in the end application. This effectively optimizes the efficiency for each
application. This feature is achieved by scaling the loss of the internal LDO based on a percentage of the
maximum output current. Note that the maximum output current is set by the K
IMAX
term and the R
ILIM
resistance
(where R
ILIM
= K
IMAX
/ I
MAX
). The flow diagram show in Figure 28 illustrates how the rectifier is dynamically
controlled (Dynamic Rectifier Control) based on a fixed percentage of the I
MAX
setting. The below table
summarizes how the rectifier behavior is dynamically adjusted based on two different R
ILIM
settings.
Table 1.
Output Current Percentage R
ILIM
= 500Ω R
ILIM
= 220 Ω V
RECT
I
MAX
= 0.5A I
MAX
= 1.14 A
0 to 10% 0 A to 0.05 A 0 A to 0.114 A 7.08 V
10 to 20% 0.05 A to 0.1A 0.114 A to 0.227 A 6.28 V
20 to 40% 0.1 A to 0.2 A 0.227 A to 0.454 A 5.53 V
>40% > 0.2 A > 0.454 A 5.11 V
Figure 9 illustrates the shift in the Dynamic Rectifier Controll behavior based on the two different R
ILIM
settings.
With the rectifier voltage (V
RECT
) being the input to the internal LDO, this adjustment in the Dynamic Rectifier
Control thresholds will dynamically adjust the power dissipation across the LDO where:
(1)
Figure 7 illustrates how the system efficiency is improved due to the Dynamic Efficiency Scaling feature. Note
that this feature balances efficiency with optimal system transient response.
R
ILIM
Calculations
The bq5101xB includes a means of providing hardware overcurrent protection by means of an analog current
regulation loop. The hardware current limit provides an extra level of safety by clamping the maximum allowable
output current (e.g. a current compliance). The R
ILIM
resistor size also sets the thresholds for the dynamic
rectifier levels and thus providing efficiency tuning per each application’s maximum system current. The
calculation for the total R
ILIM
resistance is as follows:
(2)
Where I
MAX
is the expected maximum output current during normal operation and I
ILIM
is the hardware over
current limit. When referring to the application diagram shown in Figure 2, R
ILIM
is the sum of 188 and the R
1
resistance (e.g. the total resistance from the ILIM pin to GND).
Input Overvoltage
If the input voltage suddenly increases in potential (e.g. due to a change in position of the equipment on the
charging pad), the voltage-control loop inside the bq5101xB becomes active, and prevents the output from going
beyond V
OUT-REG
. The receiver then starts sending back error packets to the transmitter every 30ms until the
input voltage comes back to the V
RECT-REG
target, and then maintains the error communication every 250ms.
If the input voltage increases in potential beyond V
OVP
, the IC switches off the LDO and communicates to the
primary to bring the voltage back to V
RECT-REG
. In addition, a proprietary voltage protection circuit is activated by
means of C
CLAMP1
and C
CLAMP2
that protects the IC from voltages beyond the maximum rating of the IC (e.g.
20V).
20 Submit Documentation Feedback Copyright © 2013, Texas Instruments Incorporated
Product Folder Links: bq51013B