bq24707
bq24707A
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SLUSA78B –JULY 2010–REVISED MARCH 2011
The ACOC function can be disabled or the threshold can be set to 1.33X, 1.66X or 2.22X of input DPM current
via SMBus command (ChargeOption() bit [2:1]).
Charge Over Current Protection (CHGOCP)
The IC has a cycle-by-cycle peak over-current protection. It monitors the voltage across SRP and SRN, and
prevents the current from exceeding of the threshold based on the DAC charge current set point. The high-side
gate drive turns off for the rest of the cycle when the over-current is detected, and resumes when the next cycle
starts.
The charge OCP threshold is automatically set to 6A, 9A, and 12A on a 10mΩ current sensing resistor based on
charge current register value. This prevents the threshold to be too high which is not safe or too low which can
be triggered in normal operation. Proper inductance should be selected to prevent OCP triggered in normal
operation due to high inductor current ripple.
Battery Over Voltage Protection (BATOVP)
The IC will not allow the high-side and low-side FET to turn-on when the battery voltage at SRN exceeds 104%
of the regulation voltage set-point. If BATOVP last over 30ms, charger is completely disabled. This allows quick
response to an over-voltage condition – such as occurs when the load is removed or the battery is disconnected.
A 4mA current sink from SRN to GND is on only during BATOVP and allows discharging the stored output
inductor energy that is transferred to the output capacitors.
Some battery pack gas gauges will set the ChargeVoltage() and ChargeCurrent() registers to 0V and 0A after the
battery pack is fully charged. If the ChargeVoltage() register is set to 0V, the bq24707 triggers BATOVP, and the
4mA current discharges the battery pack. The recommendation for bq24707 is to set the ChargeVoltage()
register to full scale charge voltage (12.592V for 3S battery for example) after the battery is fully charged. The
bq24707A will not trigger BATOVP, and there is no 4mA current to discharge the battery pack if the
ChargeVoltage() register is set 0V. The recommendation for bq24707A is to set the ChargeVoltage() register to
0V after the battery is fullycharged.
Battery Shorted to Ground (BATLOWV)
The IC will disable charge for 1ms if the battery voltage on SRN falls below 2.5V. After 1ms reset, the charge is
resumed with soft-start if all the enable conditions in the Enable and Disable Charging sections are satisfied. This
prevents any overshoot current in inductor which can saturate inductor and may damage the MOSFET. The
charge current is limited to 0.5A on 10mΩ current sensing resistor when BATLOWV condition persists and
LSFET keeps off. The LSFET turns on only for refreshing pulse to charge BTST capacitor.
Thermal Shutdown Protection (TSHUT)
The QFN package has low thermal impedance, which provides good thermal conduction from the silicon to the
ambient, to keep junctions temperatures low. As added level of protection, the charger converter turns off for
self-protection whenever the junction temperature exceeds the 155°C. The charger stays off until the junction
temperature falls below 135°C. During thermal shut down, the REGN LDO current limit is reduced to 16mA.
Once the temperature falls below 135°C, charge can be resumed with soft start.
EMI Switching Frequency Adjust
The charger switching frequency can be adjusted ±18% to solve EMI issue via SMBus command.
ChargeOption() bit [9]=0 disable the frequency adjust function. To enable frequency adjust function, set
ChargeOption() bit[9]=1. Set ChargeOption() bit [10]=0 to reduce switching frequency, set bit[10]=1 to increase
switching frequency.
If frequency is reduced, for a fixed inductor the current ripple is increased. Inductor value must be carefully
selected so that it will not trig cycle-by-cycle peak over current protection even for the worst condition such as
higher input voltage, 50% duty cycle, lower inductance and lower switching frequency.
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