BQ24072 Datasheet, PDF (28/38 Pages) Texas Instruments – 1.2A USB-FRIENDLY Li-Ion BATTERY CHARGER AND POWER-PATH MANAGEMENT IC

bq24072, bq24073
bq24074, bq24075
SLUS810A – SEPTEMBER 2008 – REVISED DECEMBER 2008...................................................................................................................................... www.ti.com
APPLICATIONS INFORMATION
bq2407x CHARGER DESIGN EXAMPLE
Refer to Figure 26 to Figure 28 for Schematics of the Design Example.
Requirements
• Supply voltage = 5V
• Fast charge current of approximately 800 mA; ISET - pin 16
• Input Current Limit =1.3A; ILIM - pin 12
• Termination Current Threshold = 110mA; ITERM – pin 15 (bq24074 only)
• Safety timer duration, Fast-Charge = 6.25 hours; TMR – pin 14
• TS – Battery Temperature Sense = 10kΩ NTC (103AT-2)
Calculations
Program the Fast Charge Current (ISET):
R_ISET = K_ISET / I_CHG
K_ISET = 890 AΩ from the electrical characteristics table.
R_ISET = 890AΩ/0.8A = 1.1125 kΩ
Select the closest standard value, which for this case is 1.13kΩ. 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 = 1550 AΩ from the electrical characteristics table.
R_ISET = 1550AΩ / 1.3A = 1.192 kΩ
Select the closest standard value, which for this case is 1.18 kΩ. Connect this resistor between ILIM (pin 12) and
V_SS.
Program the Termination Current Threshold (I_TERM) (bq24074 only)
R_ITERM = I_TERM × R_ISET / 0.030
R_ISET = 1.13 kΩ from the above calculation.
R_ITERM = 110mA × 1.13 kΩ / 0.030 = 4.143 kΩ
Select the closest standard value, which for this case is 4.12kΩ. Connect this resistor between ITERM (pin 15)
and V_SS. Note that when in USB100 mode (EN1 = EN2 = V_SS), the termination threshold is 1/3 of the normal
threshold.
Program 6.25-hour Fast-Charge Safety Timer (TMR)
R_TMR = t_MAXCHG / (10 × K_TMR)
K_TMR = 48 s/kΩ from the electrical characteristics table.
R_TMR = (6.25 hr × 3600 s/hr) / (10 × 45 s/kΩ) = 46.8kΩ
Select the closest standard value, which for this case is 46.4 kΩ. Connect this resistor between TMR (pin 2) and
V_SS.
TS Function
Use a 10kΩ NTC thermistor in the battery pack (103AT-2). For applications that do not require the TS monitoring
function, connect a 10kΩ resistor from TS to VSS to set the TS voltage at a valid level and maintain charging.
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