BQ24040 Datasheet, PDF (24/31 Pages) Texas Instruments – 800mA Single-Input Single Cell Li-Ion Battery Charger With Auto Start

bq24040
bq24041
SLUS941A – SEPTEMBER 2009 – REVISED SEPTEMBER 2009.................................................................................................................................... www.ti.com
bq24040 CHARGER APPLICATION DESIGN EXAMPLE
1.5kW
Adaptor
DC+
GND
OR
USB Port
VBUS
GND
D+
D-
1kW
1mF
2kW
bq24040
1 IN
2 ISET
3 VSS
OUT ¹⁰
1.5kW
TS ⁹
CHG 8
Battery Pack
++
4 PRETERM _ISET2 7
5 _PG
NC ⁶
System Load
1mF
VDD
TTDM/BAT_EN
ISET/100/500 mA
GND
D+
D-
Host
Requirements
• Supply voltage = 5 V
• Fast charge current: I_OUT-FC = 540 mA; ISET-pin 2
• Termination Current Threshold: %_IOUT-FC = 10% of Fast Charge or ~54mA
• Pre-Charge Current by default is twice the termination Current or ~108mA
• TS – Battery Temperature Sense = 10k NTC (103AT)
Calculations
Program the Fast Charge Current, ISET:
R_ISET = [K_(ISET) / I_(OUT)]
from electrical characteristics table. . . K_(SET) = 540AΩ
R_ISET = [540AΩ/0.54A] = 1.0 kΩ
Selecting the closest standard value, use a 1.0 kΩ resistor between ISET (pin 16) and Vss.
Program the Termination Current Threshold, ITERM:
R_PRE-TERM = K_(TERM) × %_IOUT-FC
R_PRE-TERM = 200Ω/% × 10% = 2kΩ
Selecting the closest standard value, use a 2 kΩ resistor between ITERM (pin 15) and Vss.
One can arrive at the same value by using 20% for a pre-charge value (factor of 2 difference).
R_PRE-TERM = K_(PRE-CHG) × %_IOUT-FC
R_PRE-TERM = 100Ω/% × 20%= 2kΩ
TS Function (bq24040)
Use a 10k NTC thermistor in the battery pack (103AT).
To Disable the temp sense function, use a fixed 10k resistor between the TS (Pin 1) and Vss.
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