BATTERY PROTECTION IC FOR 1-CELL PACK
S-8241 Series
Rev.7.6_00
3. Overcharge Condition
When the battery voltage becomes higher than the overcharge detection voltage (VCU) during charging under normal
condition and the state continues for the overcharge detection delay time (tCU) or longer, the S-8241 turns the charging
control FET off to stop charging. This condition is called the overcharge condition.
The overcharge condition is released in the following two cases ((1) and (2)) depending on the products with and without
overcharge hysteresis:
Products with overcharge hysteresis (overcharge detection voltage (VCU) > overcharge release voltage (VCL))
(1) When the battery voltage drops below the overcharge release voltage (VCL), the S-8241 turns the charging control
FET on and returns to the normal condition.
(2) When a load is connected and discharging starts, the S-8241 turns the charging control FET on and returns to the
normal condition. The release mechanism is as follows: the discharging current flows through an internal parasitic
diode of the charging FET immediately after a load is connected and discharging starts, and the VM pin voltage
increases about 0.7 V (Vf voltage of the diode) from the VSS pin voltage momentarily. The IC detects this voltage
(being higher than the overcurrent 1 detection voltage) and releases the overcharge condition. Consequently, in the
case that the battery voltage is equal to or lower than the overcharge detection voltage (VCU), the IC returns to the
normal condition immediately, but in the case the battery voltage is higher than the overcharge detection voltage
(VCU), the IC does not return to the normal condition until the battery voltage drops below the overcharge detection
voltage (VCU) even if the load is connected. In addition if the VM pin voltage is equal to or lower than the overcurrent
1 detection voltage when a load is connected and discharging starts, the IC does not return to the normal condition.
Remark If the battery is charged to a voltage higher than the overcharge detection voltage (VCU) and the battery
voltage does not drop below the overcharge detection voltage (VCU) even when a heavy load, which
causes an overcurrent, is connected, the overcurrent 1 and overcurrent 2 do not work until the battery
voltage drops below the overcharge detection voltage (VCU). Since an actual battery has, however, an
internal impedance of several dozens of mΩ, and the battery voltage drops immediately after a heavy load
which causes an overcurrent is connected, the overcurrent 1 and overcurrent 2 work. Detection of load
short-circuiting works regardless of the battery voltage.
Products without overcharge hysteresis (Overcharge detection voltage (VCU) = Overcharge release voltage (VCL))
(1) When the battery voltage drops below the overcharge release voltage (VCL), the S-8241 turn the charging control
FET on and returns to the normal condition.
(2) When a load is connected and discharging starts, the S-8241 turns the charging control FET on and returns to the
normal condition. The release mechanism is explained as follows : the discharging current flows through an internal
parasitic diode of the charging FET immediately after a load is connected and discharging starts, and the VM pin
voltage increases about 0.7 V (Vf voltage of the diode) from the VSS pin voltage momentarily. Detecting this voltage
(being higher than the overcurrent 1 detection voltage), the IC increases the overcharge detection voltage about 50
mV, and releases the overcharge condition. Consequently, when the battery voltage is equal to or lower than the
overcharge detection voltage (VCU) + 50 mV, the S-8241 immediately returns to the normal condition. But the
battery voltage is higher than the overcharge detection voltage (VCU) + 50 mV, the S-8241 does not return to the
normal condition until the battery voltage drops below the overcharge detection voltage (VCU) + 50 mV even if a load
is connected. If the VM pin voltage is equal to or lower than the overcurrent 1 detection voltage when a load is
connected and discharging starts, the S-8241 does not return to the normal condition.
Remark If the battery is charged to a voltage higher than the overcharge detection voltage (VCU) and the battery
voltage does not drop below the overcharge detection voltage (VCU) + 50 mV even when a heavy load,
which causes an overcurrent, is connected, the overcurrent 1 and overcurrent 2 do not work until the
battery voltage drops bellow the overcharge detection voltage (VCU) + 50 mV. Since an actual battery has,
however, an internal impedance of several dozens of mΩ, and the battery voltage drops immediately after
a heavy load which causes an overcurrent is connected, the overcurrent 1 and overcurrent 2 work.
Detection of load short-circuiting works regardless of the battery voltage.
Seiko Instruments Inc.
19
SII [ SEIKO INSTRUMENTS INC ]
