Datasheet

ACSET
DPM
AC
V
I =
20 R´
ISET2
TERM
SR
V
I =
100 R´
CHARGE TTC TTC
t = C K´
bq24630
SLUS894A –JANUARY 2010– REVISED OCTOBER 2011 www.ti.com
PRECHARGE
On powerup, if the battery voltage is below the V
LOWV
threshold, the bq24630 applies 125 mA precharge current
to the battery
(1)
. The precharge feature is intended to revive deeply discharged cells. If the V
LOWV
threshold is not
reached within 30 minutes of initiating precharge, the charger turns off and a FAULT is indicated on the status
pins.
INPUT ADAPTER CURRENT REGULATION
The total input from an ac adapter or other dc source is a function of the system supply current and the battery
charging current. System current normally fluctuates as portions of the system are powered up or down. Without
dynamic power management (DPM), the source must be able to supply the maximum system current and the
maximum charger input current simultaneously. By using DPM, the input current regulator reduces the charging
current when the input current exceeds the input current limit set by ACSET. The current capability of the ac
adaptor can be lowered, reducing system cost.
Similar to setting battery regulation current, adaptor current is sensed by resistor R
AC
connected between ACP
and ACN. Its maximum value is set by ACSET using Equation 3:
(3)
V
ACSET
, the input voltage range of ACSET is between 0 and 2 V. The ACP and ACN pins are used to sense
voltage across R
AC
with a default value of 10 mΩ. However, resistors of other values can also be used. A larger
the sense resistor gives a larger sense voltage and a higher regulation accuracy, but at the expense of higher
conduction loss.
CHARGE TERMINATION, RECHARGE, AND SAFETY TIMER
The bq24630 monitors the charging current during the voltage regulation phase. When V
TTC
is valid, termination
is detected while the voltage on the VFB pin is higher than the V
RECH
threshold AND the charge current is less
than the I
TERM
threshold, as calculated in Equation 4:
(4)
V
ISET2
, the input voltage of ISET2 is between 0 and 2 V. The minimum termination current is clamped to be
around 125 mA with a default 10-mΩ sensing resistor. To avoid early termination during WARM/COOL condition,
set I
TERM
≤ I
CHARGE
/10. As a safety backup, the bq24630 also provides a programmable charge timer. The charge
time is programmed by the capacitor connected between the TTC pin and GND, and is given by Equation 5
(5)
where C
TTC
(range from 0.047 µF to 0.47 µF to give 1-h to 10-h safety timer) is the capacitor connected from
TTC pin to GND, and K
TTC
is the constant multiplier (1.4 min/nF).
A new charge cycle is initiated and the safety timer is reset when one of the following conditions occurs:
• The battery voltage falls below the recharge threshold.
• A power-on-reset (POR) event occurs.
• CE is toggled.
The TTC pin may be taken LOW to disable termination and to disable the safety timer. If TTC is pulled to VREF,
the bq24630 continues to allow termination but disables the safety timer. TTC taken low resets the safety timer.
When ACOV, VCCLOWV, and SLEEP mode resume normal, the safety timer is reset.
POWER UP
The bq24630 uses a SLEEP comparator to determine the source of power on the VCC pin, because VCC can be
supplied either from the battery or the adapter. If the VCC voltage is greater than the SRN voltage, the bq24630
enables ACFET and disables BATFET. If all other conditions are met for charging, the bq24630 then attempts to
charge the battery (see ENABLE AND DISABLE CHARGING, Enable and Disable Charging). If the SRN voltage
is greater than VCC, indicating that the battery is the power source, the bq24630 enables the BATFET and
enters a low-quiescent-current (<15-μA) SLEEP mode to minimize current drain from the battery.
(1) Assuming a 10-mΩ sense resistor. 1.25 mV is regulated across SRP-SRN, regardless of the value of the sense resistor.
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