BQ24180 Datasheet, PDF (17/39 Pages) Texas Instruments – Fully Integrated Switch-Mode One-Cell Li-Ion Charger with Full USB Compliance and Accessory Power Connection

bq24180
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SLUSA02 A – FEBRUARY 2010 – REVISED FEBRUARY 2010
Cycle-by-cycle current limit is sensed through the internal sense MOSFETs for Q2 and Q3. The threshold for Q2
is set to a nominal 2.5-A peak current. The low-side MOSFET (Q3) also has a current limit that decides if the
PWM Controller will operate in synchronous or non-synchronous mode. This threshold is set to 100mA and it
turns off the low-side N-channel MOSFET (Q3) before the current reverses, preventing the battery from
discharging. Synchronous operation is used when the current of the low-side MOSFET is greater than 100mA to
minimize power losses.
Battery Charging Process
At the beginning of precharge, while battery voltage is below the V_PRECHARGE threshold, the bq24180 applies the
50mA precharge current, I_PRECHARGE, to the battery.
When the battery voltage is above V_PRECHARGE and below V_OREG, the charge current ramps up to fast charge
current, I_OCHARGE, or a charge current that corresponds to the input current of I_{IN_LIMIT}. The slew rate for fast
charge current is controlled to minimize the current and voltage over-shoot during transient. The input current
limit, I_{IN_LIMIT}, and fast charge current, I_OCHARGE, are programmable by the host. Once the battery voltage is close
to the regulation voltage, V_OREG, the charge current is tapered down as shown in Figure 27. The voltage
regulation feedback occurs by monitoring the battery-pack voltage between the CSOUT and PGND pins. The
bq24180 is a fixed single-cell voltage version, with adjustable regulation voltage (3.5V to 4.44V) programmed
using the I²C interface.
The bq24180 monitors the charging current during the voltage regulation phase. Once the termination threshold,
I_TERM, is detected and the battery voltage is above the recharge threshold, the bq24180 terminates charge. The
termination current level is programmable. To disable the charge current termination, the host sets the charge
termination bit (TE) of charge control register to 0, refer to I²C section for details.
A new charge cycle is initiated when one of the following conditions is detected:
1. The battery voltage falls below the V_OREG-VRCH threshold.
2. VBUS Power-on reset (POR), if battery voltage is below the V_PRECHARGE threshold
3. CE bit toggle or RESET bit is set (Host controlled)
Copyright © 2010, Texas Instruments Incorporated
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