Datasheet

1 1
1 1
5 28160 4086
1.25 0.625
7 8.236
5 5
4086 1 28160 1
1 1
0.625 1.25
IN
COLD HOT
IN IN
HOT COLD
V RCOLD RHOT
V V
R k
V V
RHOT RCOLD
V V
é ù
é ù
´ ´ ´ -
´ ´ ´ -
ê ú
ê ú
ë û ë û
= = = W
é ù é ù é ù é ù
´ - - ´ -
´ - - ´ -
ê ú ê ú ê ú ê ú
ë û ë û
ë û ë û
5
1
1
1.25
6 19.14
1 1 1 1
7 8250 28160
IN
COLD
V
V
R k
R RCOLD
-
-
= = = W
+ +
bq24072T
bq24075T, bq24079T
SLUS937A –DECEMBER 2009–REVISED APRIL 2010 www.ti.com
APPLICATION INFORMATION
bq2407xT CHARGER DESIGN EXAMPLE
Refer to Typical Application Circuits for Schematics of the Design Example.
Supply voltage = 5V
Fast charge current of approximately 800 mA; ISET – pin 16
Input Current Limit =1.35A; ILIM – pin 12
Safety timer duration, Fast-Charge = 6.25 hours; TMR – pin 14
Battery Temperature Sense = 10kΩ; NTC (103AT-2), 0°C to 50°C Operation
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
IN(MAX)
K
ILIM
= 1600 AΩ; from the electrical characteristics table.
R
ISET
= 1600AΩ / 1.35A = 1.19 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
= 45 s/kΩ from the electrical characteristics table.
R
TMR
= (6.25 hr × 3600 s/hr) / (10 x 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
Using a 10kΩ NTC thermistor in the battery pack (103AT-2). Connect a resistor divider from V
IN
to V
SS
with the
thermistor and TS connected to the center tap (R6 and R7 in typical application circuits).
R
HOT
= 4.086kΩ; 50°C threshold from NTC data sheet
R
COLD
= 28.16 kΩ; 0°C threshold from NTC data sheet
V
COLD
= 0.25 X V
IN
= 0.25 X 5V = 1.25V
V
HOT
= 0.125 X V
IN
= 0.125 X 5V = 0.625V
(3)
(4)
Since the calculated values for R6 is less than 100kΩ, a 100kΩ resistor for R8 must be used. Choose the closest
standard values, which for this case are R6=8.25kΩ and R7 = 19.1kΩ.
For applications that do not require the TS monitoring function, set R6 = 200kΩ and R7 = 49.9kΩ to set the TS
voltage at a valid level and maintain charging.
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