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BQ24105-Q1 Datasheet, PDF (13/35 Pages) Texas Instruments – SYNCHRONOUS SWITCHMODE, LI-ION AND LI-POLYMER CHARGE-MANAGEMENT IC WITH INTEGRATED POWER FETs ( bqSWITCHER™)
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bq24105-Q1
www.ti.com................................................................................................................................................................................................. SLUS953 – AUGUST 2009
The magnitude of the precharge current, IO(PRECHG), is determined by the value of programming resistor, R(ISET2),
connected to the ISET2 pin.
ǒ IO(PRECHG) + K(ISET2)
R(ISET2)
V(ISET2)
Ǔ R(SNS)
(2)
where
RSNS is the external current-sense resistor
V(ISET2) is the output voltage of the ISET2 pin
K(ISET2) is the V/A gain factor
V(ISET2) and K(ISET2) are specified in the Electrical Characteristics table.
Battery Charge Current
The battery charge current, IO(CHARGE), is established by setting the external sense resistor, R(SNS), and the
resistor, R(ISET1), connected to the ISET1 pin.
In order to set the current, first choose R(SNS) based on the regulation threshold VIREG across this resistor. The
best accuracy is achieved when the VIREG is between 100 mV and 200 mV.
R(SNS)
+
VIREG
IOCHARGE
(3)
If the results is not a standard sense resistor value, choose the next larger value. Using the selected standard
value, solve for VIREG. Once the sense resistor is selected, the ISET1 resistor can be calculated using the
following equation:
RISET1
+
KISET1
RSNS
VISET1
ICHARGE
(4)
Battery Voltage Regulation
The voltage regulation feedback occurs through the BAT pin. This input is tied directly to the positive side of the
battery pack. The bqSWITCHER monitors the battery-pack voltage between the BAT and VSS pins.
Output regulation voltage is specified as:
VOREG
=
(R1 + R2)
R2 x VIBAT
(5)
where R1 and R2 are resistor divider from BAT to FB and FB to VSS, respectively.
Recharge threshold voltage is specified as:
VRCH
=
(R1 + R2)
R2 x 50 mV
(6)
Copyright © 2009, Texas Instruments Incorporated
Product Folder Link(s): bq24105-Q1
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