BQ24616 Datasheet, PDF (16/34 Pages) Texas Instruments – JEITA Guideline Compatible Stand-Alone Synchronous Switch-Mode Li-Ion or Li-Polymer Battery Charger with System Power Selector and Low Iq

bq24616
SLUSA49A – APRIL 2010 – REVISED MAY 2010
www.ti.com
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 battery charger 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
sense resistor will give a larger sense voltage and a higher regulation accuracy, but at the expense of higher
conduction loss.
Precharge
On power-up, if the battery voltage is below the V_LOWV threshold, the bq24616 applies the precharge current to
the battery. This 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.
The precharge current (I_PRECHARGE) is determined by the voltage on the ISET2 pin (V_ISET2) according to
Equation 4.
I_PRECHARGE =
V_ISET2
100 ´ R_SR
(4)
Charge Termination, Recharge, and Safety Timer
The bq24616 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 5:
I_TERM =
V_ISET2
100 ´ R_SR
(5)
V_ISET2, the input voltage of ISET2, is between 0 and 2V. The minimum precharge/termination current is clamped
to be around 125mA with default 10mΩ sensing resistor. As a safety backup, the bq24616 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 6
t_CHARGE = C_TTC ´ K_TTC
(6)
where C_TTC (range from 0.01µF to 0.11 µF to give 1-10hr safety time) is the capacitor connected from TTC pin to
GND, and K_TTC is the constant multiplier (5.6min/nF).
A new charge cycle is initiated and fast-charge 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 bq24616 will continue to allow termination but disable safety timer. TTC taken low will reset the safety timer.
When ACOV, VCCLOWV and SLEEP mode resume normal, the safety timer will also be reset.
16
Submit Documentation Feedback
Product Folder Link(s): bq24616
Copyright © 2010, Texas Instruments Incorporated