Data Sheet

bq24072 , bq24073 , bq24074 , bq24075 , bq24079
SLUS810K –SEPTEMBER 2008–REVISED MARCH 2015 www.ti.com
Typical Application (continued)
10.2.1 Design Requirements
• Supply voltage = 5 V
• Fast charge current of approximately 800 mA; ISET - pin 16
• Input Current Limit =1.3 A; ILIM - pin 12
• Termination Current Threshold = 110 mA; ITERM – pin 15 (bq24074 only)
• Safety timer duration, Fast-Charge = 6.25 hours; TMR – pin 14
• TS – Battery Temperature Sense = 10 k Ω NTC (103AT-2)
10.2.2 Detailed Design Procedure
10.2.2.1 bq2407x Charger Design Example
See Figure 30 to Figure 42 for Schematics of the Design Example.
10.2.2.1.1 Termination Disable (TD) (bq24072, bq24073 only)
Connect TD high to disable termination. Connect TD low to enable termination.
10.2.2.1.2 System ON/OFF (SYSOFF) (bq24075 or bq24079 only)
Connect SYSOFF high to disconnect the battery from the system load. Connect SYSOFF low for normal
operation
10.2.2.2 Calculations
10.2.2.2.1 Program the Fast Charge Current (ISET):
R
ISET
= K
ISET
/ I
CHG
K
ISET
= 890 AΩ from the electrical characteristics table.
R
ISET
= 890 AΩ / 0.8 A = 1.1125 kΩ
Select the closest standard value, which for this case is 1.13 kΩ. Connect this resistor between ISET (pin 16)
and V
SS
.
10.2.2.2.2 Program the Input Current Limit (ILIM)
R
ILIM
= K
ILIM
/ I
I_MAX
K
ILIM
= 1550 AΩ from the electrical characteristics table.
R
ISET
= 1550 AΩ / 1.3 A = 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
.
10.2.2.2.3 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
= 110 mA × 1.13 kΩ / 0.030 = 4.143 kΩ
Select the closest standard value, which for this case is 4.12 kΩ. 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.
10.2.2.2.4 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) = 46.8 kΩ
Select the closest standard value, which for this case is 46.4 kΩ. Connect this resistor between TMR (pin 2) and
V
SS
.
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