bq51010
bq51011
bq51013
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SLVSAT9B –APRIL 2011–REVISED AUGUST 2011
Dynamic Communication Current Limit (Dynamic ILIM
)
The bq51011 employs the dynamic communication current limit feature in order to enable the communication
current limit only when the power supply is operating in current limit mode (IOUT = IILIM). This is illustrated in
Figure 23 where the output current is transitioned from IOUT < IILIM to IOUT = IILIM. This allows for systems to
startup without the current limit enabled in order to provide better system performance (e.g. during a dead battery
condition). The current limit is used during rectifier tracking mode to ensure stability of the communication back to
the WPC transmitter. This adds robustness to the communication link.
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 utilized for monitoring the
surface that can be exposed to the end user (e.g. place the NTC resistor closest to the user).
Figure 27 allows for any NTC resistor to be used with the given VHOT and VCOLD thresholds.
VTSB
R2
TS /CTRL
R3
NTC
Figure 27. NTC Circuit Used for Safe Operation of the Wireless Receiver Power Supply
The resistors R2 and R3 can be solved by resolving the system of equations at the desired temperature
thresholds. The two equations are:
æ
ç
ç
ç
ö
÷
÷
÷
R3 RNTC
TCOLD
÷
çR3 + R
÷
è
TCOLD ø
NTC
%VCOLD
=
× 100
æ
ç
ç
ç
ö
R3 RNTC
÷
TCOLD
÷
+ R2
÷
÷
÷
çR3 + R
è
TCOLD ø
NTC
(1)
æ
ö
R3 RNTC
÷
ç
THOT
÷
ç
÷
THOT ø
ç
÷
çR3 + R
÷
è
NTC
%VHOT
=
× 100
æ
ç
ç
ç
ö
÷
÷
R3 RNTC
THOT
+ R2
÷
÷
çR3 + R
÷
è
THOT ø
NTC
(2)
(3)
Where:
1
1
-
β
(
)
TCOLD To
RNTC
= ROe
= ROe
TCOLD
THOT
1
1
β
-
)
(
THOT To
RNTC
where, TCOLD and THOT are the desired temperature thresholds in degrees Kelvin. Ro is the nominal resistance
and β is the temperature coefficient of the NTC resistor. An example solution for an NTC resistor with RO = 10KΩ
and β = 4500 is:
•
R2 = 7.81kΩ
Copyright © 2011, Texas Instruments Incorporated
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