Datasheet

bq24610
bq24617
www.ti.com SLUS892B –DECEMBER 2009–REVISED SEPTEMBER 2013
recharged and able to keep the high-side power MOSFET on during the next cycle. This is important for battery
chargers, where unlike regular dc-dc converters, there is a battery load that maintains a voltage and can both
source and sink current. The 80-ns low-side pulse pulls the PH node (connection between high and low-side
MOSFET) down, allowing the bootstrap capacitor to recharge up to the REGN LDO value. After the 80 ns, the
low-side MOSFET is kept off to prevent negative inductor current from occurring.
At very low currents during non-synchronous operation, there may be a small amount of negative inductor
current during the 80-ns recharge pulse. The charge should be low enough to be absorbed by the input
capacitance. Whenever the converter goes into zero-percent duty cycle, the high-side MOSFET does not turn on,
and the low-side MOSFET does not turn on (only 80 ns recharge pulse) either, and there is almost no discharge
from the battery.
During the DCM mode the loop response automatically changes and has a single-pole system at which the pole
is proportional to the load current, because the converter does not sink current, and only the load provides a
current sink. This means at very low currents the loop response is slower, as there is less sinking current
available to discharge the output voltage.
Cycle-by-Cycle Charge Undercurrent Protection
If the SRP-SRN voltage decreases below 5 mV (the charger is also forced into non-synchronous mode when the
average SRP-SRN voltage is lower than 1.25 mV), the low-side FET is turned off for the remainder of the
switching cycle to prevent negative inductor current. During DCM, the low-side FET only turns on for around 80
ns when the bootstrap capacitor voltage drops below 4.2 V to provide refresh charge for the bootstrap capacitor.
This is important to prevent negative inductor current from causing a boost effect in which the input voltage
increases as power is transferred from the battery to the input capacitors and leads to an overvoltage stress on
the VCC node and potentially causes damage to the system.
Input Overvoltage Protection (ACOV)
ACOV provides protection to prevent system damage due to high input voltage. Once the adapter voltage
reaches the ACOV threshold, charge is disabled and the system is switched to the battery instead of the adapter.
Input Undervoltage Lock Out (UVLO)
The system must have a minimum VCC voltage to allow proper operation. This VCC voltage could come from
either input adapter or battery, because a conduction path exists from the battery to VCC through the high-side
NMOS body diode. When VCC is below the UVLO threshold, all circuits on the IC are disabled, and the gate-
drive bias to ACFET and BATFET is disabled.
Battery Overvoltage Protection
The converter does not allow the high-side FET to turn on until the BAT voltage goes below 102% of the
regulation voltage. This allows one-cycle response to an overvoltage condition, such as occurs when the load is
removed or the battery is disconnected. An 8-mA current sink from SRP to GND is on only during charge and
allows discharging the stored output inductor energy that is transferred to the output capacitors. BATOVP also
suspends the safety timer.
Cycle-by-Cycle Charge Overcurrent Protection
The charger has a secondary cycle-to-cycle overcurrent protection. It monitors the charge current, and prevents
the current from exceeding 160% of the programmed charge current. The high-side gate drive turns off when the
overcurrent is detected, and automatically resumes when the current falls below the overcurrent threshold.
Thermal Shutdown Protection
The QFN package has low thermal impedance, which provides good thermal conduction from the silicon to the
ambient, to keep junction temperatures low. As an added level of protection, the charger converter turns off and
self-protects whenever the junction temperature exceeds the TSHUT threshold of 145°C. The charger stays off
until the junction temperature falls below 130°C; then the charger will soft-start again if all other enable charge
conditions are valid. Thermal shutdown also suspends the safety timer.
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