BQ24230 Datasheet, PDF (24/33 Pages) Texas Instruments – USB-FRIENDLY LITHIUM-ION BATTERY CHARGER AND POWER-PATH MANAGEMENT IC

bq24230
bq24232
SLUS821A – OCTOBER 2008 – REVISED DECEMBER 2008 .......................................................................................................................................... www.ti.com
APPLICATIONS INFORMATION
bq24232 CHARGER DESIGN EXAMPLE
See Figure 18 for the Design Example Schematic.
Requirements
• Supply voltage = 5 V
• Fast-charge current of approximately 200 mA; ISET - pin 16
• Input Current Limit =500 mA; ILIM - pin 12
• Termination Current = 25 mA - pin 15
• Safety timer duration, Fast charge = 6.25 hours; TMR – pin 14
• TS – Battery Temperature Sense = 10 kΩ NTC (103AT-2)
Calculations
Program the Fast-Charge Current (ISET):
R_ISET = K_ISET / I_CHG
K_ISET = 870 AΩ from the electrical characteristics table.
R_ISET = 870 AΩ/0.2 A = 4.35kΩ
Select the closest standard value, which for this case is 4.32 kΩ. Connect this resistor between ISET (pin 16)
and V_SS.
Program the Input Current Limit (ILIM)
R_ILIM = K_ILIM / I_{I_MAX}
K_ILIM = 1470 AΩ from the electrical characteristics table.
R_ISET = 1470 AΩ / 0.5 A = 2.94 kΩ
Select the closest standard value, which for this case is 2.94 kΩ. Connect this resistor between ILIM (pin 12) and
V_SS.
Program the Termination Current Threshold (ITERM)
R_ITERM = R_ISET × I_TERM / K_ITERM
K_ITERM = 0.03 A from electrical characteristics table
R_ITERM = 4.32 kΩ × 0.025 A/0.03 A = 3.6 kΩ
Select the closest standard value, which for this case is 3.57 kΩ. Connect this resistor between ITERM (pin 15)
and V_SS
Program 6.25-Hour Fast-Charge Safety Timer (TMR)
R_TMR = t_MAXCHG / (10 × K_TMR)
K_TMR = 40 s/kΩ from the electrical characteristics table.
R_TMR = (6.25 hr × 3600 s/hr) / (10 × 40 s/kΩ) = 56.25 kΩ
Select the closest standard value, which for this case is 56.2 kΩ. Connect this resistor between TMR (pin 2) and
V_SS.
TS Function
Use a 10-kΩ NTC thermistor in the battery pack (103AT). To disable the temperature sense function, use a fixed
10-kΩ resistor between the TS (pin 1) and V_SS. Pay close attention to the linearity of the chosen NTC so that it
provides the desired hot and cold turnoff thresholds.
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