Datasheet

BatteryPack
VBUS
GND
D+
D-
USBPort
DC+
GND
Adaptor
VDD
D-
D+
GND
TTDM
Host
SystemLoad
OR
ISET/100/500 mA
1
2
3
4
5
10
9
8
7
6
IN
ISET
VSS
PRETERM
PG
NC
ISET2
CHG
TS
OUT
bq24090
+
+
1 Fm
1 Fm
1kW
1.5kW
1.5kW
2kW
bq24090, bq24091
bq24092, bq24093
SLUS968A –JANUARY 2010–REVISED FEBRUARY 2010 www.ti.com
bq24090 CHARGER APPLICATION DESIGN EXAMPLE
Requirements
• Supply voltage = 5 V
• Fast charge current: I
OUT-FC
= 540 mA; ISET-pin 2
• Termination Current Threshold: %
IOUT-FC
= 10% of Fast Charge or ~54mA
• Pre-Charge Current by default is twice the termination Current or ~108mA
• TS – Battery Temperature Sense = 10k NTC (103AT)
Calculations
Program the Fast Charge Current, ISET:
R
ISET
= [K
(ISET)
/ I
(OUT)
]
from electrical characteristics table. . . K
(SET)
= 540AΩ
R
ISET
= [540AΩ/0.54A] = 1.0 kΩ
Selecting the closest standard value, use a 1.0 kΩ resistor between ISET (pin 16) and Vss.
Program the Termination Current Threshold, ITERM:
R
PRE-TERM
= K
(TERM)
× %
IOUT-FC
R
PRE-TERM
= 200Ω/% × 10% = 2kΩ
Selecting the closest standard value, use a 2 kΩ resistor between ITERM (pin 15) and Vss.
One can arrive at the same value by using 20% for a pre-charge value (factor of 2 difference).
R
PRE-TERM
= K
(PRE-CHG)
× %
IOUT-FC
R
PRE-TERM
= 100Ω/% × 20%= 2kΩ
TS Function
Use a 10k NTC thermistor in the battery pack (103AT).
To Disable the temp sense function, use a fixed 10k resistor between the TS (Pin 1) and Vss.
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Product Folder Link(s): bq24090 bq24091