bq24170
bq24172
www.ti.com
SLUSAD2A –NOVEMBER 2010–REVISED NOVEMBER 2010
V
ISET
ICHARGE
=
20 ´ RSR
(2)
The valid input voltage range of ISET is up to 0.8V. With 10mΩ sense resistor, the maximum output current is
4A. With 20mΩ sense resistor, the maximum output current is 2A.
The charger is disabled when ISET pin voltage is below 40mV and is enabled when ISET pin voltage is above
120mV. For 10mΩ current sensing resistor, the minimum fast charge current must be higher than 600mA.
Under high ambient temperature, the charge current will fold back to keep IC temperature not exceeding 120°C.
BATTERY PRECHARGE CURRENT REGULATION
On Power-up, if the battery voltage is below the VLOWV threshold, the bq24170/172 applies the pre-charge
current to the battery. This pre-charge feature is intended to revive deeply discharged cells. If the VLOWV
threshold is not reached within 30 minutes of initiating pre-charge, the charger turns off and a FAULT is indicated
on the status pins.
For bq24170/172, the pre-charge current is set as 10% of the fast charge rate set by ISET voltage.
V
ISET
IPRECHARGE
=
200 ´ RSR
(3)
INPUT CURRENT REGULATION
The total input current from an AC adapter or other DC sources is a function of the system supply current and
the battery charging current. System current normally fluctuated as portions of the systems are powered up or
down. Without Dynamic Power Management (DPM), the source must be able to supply the maximum system
current and the maximum available charger input current simultaneously. By using DPM, the input current
regulator reduces the charging current when the summation of system power and charge power exceeds the
maximum input power. Therefore, the current capability of the AC adapter can be lowered, reducing system cost.
Input current is set by the voltage on ACSET pin using the following equation:
VACSET
IDPM
=
20 ´ RAC
(4)
The ACP and ACN pins are used to sense across RAC with default value of 10mΩ. However, resistors of other
values can also be used. A larger sense resistor will give a larger sense voltage and higher regulation accuracy,
at the expense of higher conduction loss.
CHARGE TERMINATION, RECHARGE, AND SAFETY TIMERS
The charger monitors the charging current during the voltage regulation phase. Termination is detected when the
SRN voltage (bq24170) or FB voltage (bq24172) is higher than recharge threshold and the charge current is less
than the termination current threshold, as calculated below:
V
ISET
ITERM
=
200 ´ RSR
(5)
where VISET is the voltage on the ISET pin and RSR is the sense resistor. There is a 25ms deglitch time during
transition between fast-charge and pre-charge.
As a safety backup, the charger also provides an internal fixed 30 minutes pre-charge safety timer and a
programmable fast charge timer. The fast charge time is programmed by the capacitor connected between the
TTC pin and AGND, and is given by the formula:
tTTC = CTTC ´KTTC
(6)
Where CTTC is the capacitor connected to TTC and KTTC is the constant multiplier.
A new charge cycle is initiated when one of the following conditions occurs:
•
•
•
The battery voltage falls below the recharge threshold
A power-on-reset (POR) event occurs
ISET pin toggled below 40mV (disable charge) and above 120mV (enable charge)
Copyright © 2010, Texas Instruments Incorporated
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