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SS6821
APPLICATION INFORMATION
OPERATION
Over-charge Protection
When the voltage of the battery cell exceeds
the overcharge protection voltage (VOCP) for
longer than the overcharge delay time (TOC)
period, charging is halted by turning off the
charge control MOSFET M2. The overcharge
delay time is fixed to 100ms by circuitry
internal to the IC. The over-charge condition is
released in one of two ways:
1. The voltage of the battery cell becomes
lower than the over-charge release voltage
(VOCR or VOCP- VHYS) through self-discharge.
2.
The voltage of the battery cell falls below
the over-charge protection voltage (VOCP)
because a load has been connected.
When the battery voltage is above VOCP, the
over-charge condition is never released even if
a load is connected to the pack.
Over-discharge protection
When the voltage of the battery cell goes
below the over-discharge protection voltage
(VODP) for longer than the over-discharge delay
time (TOD) period, discharging is halted by
turning off the discharge control MOSFET M1.
The over-discharge delay time defaults to
10ms. Discharging is immediately resumed
when the voltage of the battery cell becomes
higher than over-discharge release voltage
(VODR) through charging.
Over-current protection
In normal mode, the SS6821 continuously
monitors the discharge current by sensing the
voltage of the CS pin. If the voltage of the CS
pin exceeds the over-current protection voltage
(VOIP) for longer than the over-current delay
time (TOI) period, the over-current protection
circuit operates and discharging is halted by
turning off of the discharge control MOSFET M1.
The over-current condition returns to the normal
mode when the load is released and the
impedance between the BATT+ and BATT-
terminals is 1M
Ω or higher.
The SS6821 is provided with two over-
current detection levels (0.2V and 1V) and two
over-current
delay
times
(TOI1
and
TOI2)
corresponding to each over-current detection
level.
Load detection after overcharge
The load detection function after over-charge is
implemented by detecting the CS pin voltage.
Once a load is connected to the battery pack
after an over-charge, discharge current flows
through the parasitic diode of MOSFET M2 and
there is a diode voltage drop between CS and
GND. A load is determined to be connected to
the pack if the CS pin voltage is above the load
detection threshold voltage (VLD).
Power-down after over-discharge
When an over-discharge occurs, the SS6821
will go into power-down mode, turning off all the
timing generation and detection circuitry to
reduce
the
quiescent
current
to
0.6
µA
(VCC=2.2V). At the same time, the CS pin is
pulled high to VCC through a high resistance
resistor.
Charge detection after over-discharge
When over-discharge occurs, the discharge
control MOSFET M1 turns off and discharging is
halted. However, charging is still permitted
through the parasitic diode of M1. Once the
charger is connected to the battery pack, the
SS6821 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 the charge
detection threshold voltage (VCH).
.
12/6/2004 Rev.2.02
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