BQ24618 Datasheet, PDF (16/36 Pages) Texas Instruments – Stand-Alone USB-Friendly Synchronous Switch-Mode Li-Ion or Li-Polymer Battery Charger

bq24618
SLUSA55 – OCTOBER 2010
Regulation Voltage
V_RECH
Regulation Current
Precharge
Current
Regulation
Phase
DETAILED DESCRIPTION
Fastcharge Current
Regulation Phase
Fastcharge Voltage
Regulation Phase
Charge
Current
www.ti.com
Termination
V_LOWV
I_PRECH & I _TERM
Charge
Voltage
Precharge
Time
Fastcharge Safety Time
Figure 17. Typical Charging Profile
Battery Voltage Regulation
The bq24618 uses a high accuracy voltage band gap and regulator for the high charging voltage accuracy. The
charge voltage is programmed via a resistor divider from the battery to ground, with the midpoint tied to the VFB
pin. The voltage at the VFB pin is regulated to 2.1V, giving the following equation for the regulation voltage:
VBA _T
= 2.1
V
´
é
êë¹⁺
R2
R1
ù
úû
,
(1)
where R2 is connected from VFB to the battery and R1 is connected from VFB to GND.
Battery Current Regulation
The ISET1 input sets the maximum fast charging current. Battery charge current is sensed by resistor R_SR
connected between SRP and SRN. The full-scale differential voltage between SRP and SRN is 100mV. Thus, for
a 10mΩ sense resistor, the maximum charging current is 10A. The equation for charge current is:
I_CHARGE
=
V_ISET1
20 ´ R_SR
(2)
V_ISET1, the input voltage range of ISET1 is between 0V and 2V. The SRP and SRN pins are used to sense
voltage across R_SR with default value of 10mΩ. However, resistors of other values can also be used. A larger
sense resistor will give a larger sense voltage, a higher regulation accuracy; but, at the expense of higher
conduction loss.
16
Submit Documentation Feedback
Product Folder Link(s): bq24618
Copyright © 2010, Texas Instruments Incorporated