BQ24630 Datasheet, PDF (15/33 Pages) Texas Instruments – Stand-Alone Synchronous Switch-Mode Lithium Phosphate Battery Charger with System Power Selector and Low Iq

bq24630
www.ti.com
SLUS894 – JANUARY 2010
PRECHARGE
On power-up, if the battery voltage is below the V_LOWV threshold, the bq24630 applies 125mA 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 sources is a function of the system supply current and the battery
charging current. System current normally fluctuates 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 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:
I_DPM
=
V_ACSET
20 ´ R_AC
(3)
V_ACSET, the input voltage range of ACSET is between 0 and 2V. The ACP and ACN pins are used to sense
voltage across R_AC with default value of 10mΩ. However, resistors of other values can also be used. A larger the
sense resistor will give 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:
I_TERM =
V_ISET2
100 ´ R_SR
(4)
V_ISET2, the input voltage of ISET2 is between 0 and 2V. The minimum termination current is clamped to be
around 125mA with default 10mΩ 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
t_CHARGE = C_TTC ´ K _TTC
(5)
where C_TTC (range from 0.047µF to 0.47µF to give 1-10hr safety timer) is the capacitor connected from TTC pin
to GND, and K_TTC is the constant multiplier (1.4min/nF).
A new charge cycle is initiated and safety timer is reset when one of the following conditions occur:
• 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 will continue to allow termination but disable the safety timer. TTC taken low will reset the safety
timer. When ACOV, VCCLOWV and SLEEP mode resume normal, the safety timer will be reset.
(1) assuming a 10mΩ sense resistor. 1.25mV will be regulated across SRP-SRN, regardless of the value of the sense resistor.
Copyright © 2010, Texas Instruments Incorporated
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