Datasheet

bq24072, bq24073
bq24074, bq24075, bq24079
www.ti.com SLUS810I –SEPTEMBER 2008–REVISED JANUARY 2014
APPLICATIONS INFORMATION
bq2407x CHARGER DESIGN EXAMPLE
See 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 = 10k Ω 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 × 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 © 2008–2014, Texas Instruments Incorporated Submit Documentation Feedback 29
Product Folder Links: bq24072 bq24073 bq24074 bq24075 bq24079