AIC1803 Datasheet, PDF (9/12 Pages) Analog Intergrations Corporation – Three-Cell Lithium-Ion Battery Protection IC

beyond the overdischarge delay time (T_OD) period,
discharging is inhibited by the turning-off of the
discharge control MOSFET M1. The
overdischarge delay time is set by the external
capacitor C_TD. Inhibition of discharging is
immediately released when the voltage of the
overdischarge cell becomes higher than the
overdischarge release voltage (V_ODR) through
charging.
Overcurrent Protection
In normal mode, the AIC1803 continuously
monitors the discharge current by sensing the
voltage of CS pin. If the voltage V_CC-V_CS exceeds
the overcurrent protection voltage (V_OIP) beyond
the overcurrent delay time (T_OI) period, the
overcurrent protection circuit operates and
discharging is inhibited by the turning-off of the
discharge control MOSFET M1. Discharging must
be inhibited for at least 256mS after overcurrent
takes place to avoid damage to external control
MOSFETs due to rapidly switching transient
between BATT+ and BATT- terminals. The
overcurrent condition returns to normal mode
when the load is released and the impedance
between the BATT+ and BATT- terminals is
20MΩ or higher.
The AIC1803 is provided with the three
overcurrent detection levels (0.15V, 0.3V and
1.0V) and the three overcurrent delay time (T_OI1,
T_OI2 and T_OI3) corresponding to each overcurrent
detection level. T_OI1 is set by the external capacitor
C_TI. T_OI2 and T_OI3 default to 4mS and 300µs
respectively, and can not be adjusted due to
protection of external MOSFETs
Cell-Balancing
Overcharge
Bleeding
after
When either of the battery cells is overcharged,
the AIC1803 provides the cell-balancing bleeding
function to discharge the overcharged cell at
about 9mA until the voltage of the overcharged
cell decreases to overcharge release voltage
AIC1803
(V_OCR or V_OCP-v_HYS). This function is accomplished
by connecting UD1, UD2, UD3 pins to the positive
terminals of battery cells BAT1, BAT2, BAT3
respectively. The bleeding current can be
decreased by inserting resistors along UD1 pin to
BAT1 positive terminal path and UD3 pin to BAT3
positive terminal path.
Power-Down after Overdischarge
When overdischarge occurs, the AIC1803 will go
into power-down mode, turning off all the timing
generation and detection circuitry to reduce the
quiescent current to about 1.3µA (V_CC=6.9V). In
the unusual case where one battery cell is
overdischarged while another one under
overcharge condition, the AIC1803 will turn off all
the detection circuitry except the overcharge
detection circuit for the cell under overcharge
condition.
Charge Detection after Overdischarge
When overdischarge occurs, the discharge control
MOSFET M1 turns off and discharging is inhibited.
However, charging is still permitted through the
parasitic diode of M1. Once the charger is
connected to the battery pack, the AIC1803
immediately turns on all the timing generation and
detection circuitry and goes into normal mode.
Charging is determined to be in progress if the CS
pin voltage is higher than VCC + 0.4V (charge
detection threshold voltage V_CH).
• DESIGN GUIDE
Setting the Overcharge and
Overdischarge Delay Time
The overcharge delay time is set by the external
capacitor C_TC and the overdischarge delay time is
set by the external capacitor C_TD. The relationship
between capacitance of the external capacitors
and delay time is tabulated as below.
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