AIC1821 Datasheet, PDF (5/7 Pages) Analog Intergrations Corporation – ONE-CELL LITHIUM-ION BATTERY PROTECTION IC

AIC1821
ONE-CELL LITHIUM-ION BATTERY PROTECTION IC
SPEC NO: DS-1821-P1 06/07/00
n APPLICATION INFORMATIONS
l THE OPERATION
Overcharge Protection
When the voltage of the battery cell exceeds the
overcharge protection voltage (V_OCP) beyond the
overcharge delay time (T_OC) period, charging is
inhibited by the turning-off of the charge control
MOSFET M2. The overcharge delay time is fixed to
100mS by IC internal circuit. The overcharge
condition is released in two cases:
1. The voltage of the battery cell becomes lower
than the overcharge release voltage (V_OCR or
V_OCP- V_HYS) through self-discharge.
2. The voltage of the battery cell falls below the
overcharge protection voltage (V_OCP) and a load
is connected.
When the battery voltage is above V_OCP, the
overcharge condition is never released even a load
is connected to the pack.
Overdischarge Protection
When the voltage of the battery cell goes below the
overdischarge protection voltage (V_ODP) 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
defaults to 100mS. Inhibition of discharging is
immediately released when the voltage of the
battery cell becomes higher than overdischarge
release voltage (V_ODR) through charging.
Overcurrent Protection
In normal mode, the AIC1821 continuously monitors
the discharge current by sensing the voltage of CS
pin. If the voltage of CS pin 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.
The overcurrent condition returns to the normal
mode when the load is released and the impedance
between the BATT+ and BATT- terminals is 20MΩ
or higher.
The AIC1821 is provided with the two overcurrent
detection levels (0.2V and 1V) and the two
overcurrent delay time (T_OI1 and T_OI2) corresponding
to each overcurrent detection level.
Load Detection after Overcharge
The load detection function after overcharge is
implemented by detecting the CS pin voltage. Once
a load is connected to the battery pack after
overcharge, discharge current flows through the
parasitic diode of MOSFET M2 and there is a diode
voltage drop between CS and GND. Load is
determined to be connected to the pack if the CS
pin voltage is above load detection threshold
voltage (V_LD).
Power-Down after Overdischarge
When overdischarge occurs, the AIC1821 will go
into power-down mode, turning off all the timing
generation and detection circuitry to reduce the
quiescent current to 0.4µA (V_CC=2.3V). At the same
time, the CS pin is pull-high to VCC through a high
resistance resistor.
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 AIC1821
immediately turns on all the timing generation and
detection circuitry. Charging is determined to be in
progress if the voltage between CS and GND is
below charge detection threshold voltage (V_CH).
l DESIGN GUIDE
Selection of External Control MOSFETs
Because the overcurrent protection voltage is
preset, the threshold current for overcurrent
detection is determined by the turn-on resistance of
the discharge control MOSFET M1. The turn-on
resistance of the external control MOSFETs can be
determined by the equation: R_ON=V_OIP/ (2 x I_T) (I_T is
the overcurrent threshold current). For example, if
the overcurrent threshold current _TI is designed to
be 3A, the turn-on resistance of the external control
MOSFETs must be 33mΩ. Users should be aware
that turn-on resistance of the MOSFET changes
with temperature variation due to heat dissipation. It
changes with the voltage between gate and source
as well. (Turn-on resistance of a MOSFET
increases as the voltage between gate and source
decreases). Once the turn-on resistance of the
external MOSFET changes, the overcurrent
threshold current will change accordingly.
Suppressing the Ripple and Disturbance
from Charger
To suppress the ripple and disturbance from
charger, connecting R1, C1 to VCC pin is
recommended.
Protection at CS pin
R2 is used for latch-up protection when charger is
ANALOG INTEGRATIONS CORPORATION
4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C.
www.analog.com.tw
TEL: [phone] FAX:[phone]
5