BQ24140_14 Datasheet, PDF (17/39 Pages) Texas Instruments – Integrated Dual-Input Switch-Mode One-Cell Li-Ion Charger with Full USB Compliance and USB-OTG Support

bq24140
www.ti.com
SLUSAO5 – OCTOBER 2011
Cycle-by-cycle current limit is sensed through FETs Q4 and Q5 for the high side current limit and through Q3 and
Q6 for the low side current limit. The high side current limit threshold is set to a nominal 2.4-A peak current. The
low-side current limit 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 FETs (Q3 and/or Q6) before the current
reverses, preventing the battery from discharging. Synchronous operation is used when the current of the
low-side FET is greater than 100mA to minimize power losses.
If the battery voltage is below the V(_SHORT) threshold, the bq24140 applies the short circuit current, I(_SHORT), to
the battery. The purpose of this current is to close an open protector on the battery pack. Once the battery
voltage rises above V_SHORT, the bq24140 ramps us the charge current to the programmed I_CHARGE value. If the
programmed charge current requires an input current that is higher than the programmed I_{IN_LIMIT} value, then the
bq24140 will regulate the input current and the charge current will be limited by the input current loop. The slew
rate for fast charge current is controlled to minimize the current and voltage over-shoot during transient. Both the
input current limit, I_{IN_LIMIT}, and fast charge current, I_CHARGE, can be set by the host. Once the battery voltage
reaches the programmed regulation voltage, V_OREG, the charge current is tapered down. (See Figure 16 and
Figure 17.
Precharge Phase
V_OREG ^{(Linear Charge)}
Fastcharge Phase
(PWM Charge)
Voltage Regulation Phase
(PWM Charge)
I_CHARGE
Charge Voltage
V_SHORT
Termination
I_SHORT
Charge Current
Figure 16. Typical Charging Profile for No Input Current Limit
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