BQ24075-Q1_15 Datasheet, PDF (27/38 Pages) Texas Instruments – SLUSAU3B –FEBRUARY 2012–REVISED MARCH 2012

bq24075-Q1
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SLUSAU3B – FEBRUARY 2012 – REVISED MARCH 2012
APPLICATIONS INFORMATION
bq24075-Q1 CHARGER DESIGN EXAMPLE
See Figure 19 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
• 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 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 × 48 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.
Copyright © 2012, Texas Instruments Incorporated
Product Folder Link(s): bq24075-Q1
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