Datasheet

BATTERY PROTECTION IC FOR SINGLE-CELL PACK
S-8261 Series
Rev.4.1_00
Seiko Instruments Inc.
20
 Operation
Remark Refer to the “ Battery Protection IC Connection Example”.
1. Normal Condition
The S-8261 Series monitors the voltage of the battery connected between VDD pin and VSS pin and the voltage
difference between VM pin and VSS pin to control charging and discharging. When the battery voltage is in the range
from the overdischarge detection voltage (V
DL
) to the overcharge detection voltage (V
CU
), and the VM pin voltage is in
the range from the charger detection voltage (V
CHA
) to the overcurrent 1 detection voltage (V
IOV1
), the IC turns both the
charging and discharging control FETs on. This condition is called the normal condition, and in this condition charging
and discharging can be carried out freely.
Caution When a battery is connected to the IC for the first time, discharging may not be enabled. In this
case, short the VM pin and VSS pin or connect the charger to restore the normal condition.
2. Overcurrent Condition (Detection of Overcurrent 1, Overcurrent 2 and Load Short-circuiting)
When a battery in the normal status is in the status where the voltage of the VM pin is equal to or higher than the
overcurrent detection voltage because the discharge current is higher than the specified value and the status lasts for
the overcurrent detection delay time, the discharge control FET is turned off and discharging is stopped. This status is
called the overcurrent status.
In the overcurrent status, the VM and VSS pins are shorted by the resistor between VM and VSS (R
VMS
) in the IC.
However, the voltage of the VM pin is at the V
DD
potential due to the load as long as the load is connected. When the
load is disconnected, the VM pin returns to the V
SS
potential.
This IC detects the status when the impedance between the EB+ pin and EB− pin (Refer to Figure 11) increases and is
equal to the impedance that enables automatic restoration and the voltage at the VM pin returns to overcurrent 1
detection voltage (V
IOV1
) or lower and the overcurrent status is restored to the normal status.
Caution The impedance that enables automatic restoration varies depending on the battery voltage and the
set value of overcurrent 1 detection voltage.
3. Overcharge Condition
When the battery voltage becomes higher than the overcharge detection voltage (V
CU
) during charging
under the normal condition and the detection continues for the overcharge detection delay time (t
CU
) or
longer, the S-8261 Series turns the charging control FET off to stop charging. This condition is called the
overcharge condition.
The overcharge condition is released by the following two cases ((1) and (2)):
(1) When the battery voltage falls below the overcharge release voltage (V
CU
) − overcharge detection hysteresis
voltage (V
HC
), the S-8261 Series turns the charging control FET on and turns to the normal condition.
(2) When a load is connected and discharging starts, the S-8261 Series turns the charging control FET on and returns
to the normal condition. Just after the load is connected and discharging starts, the discharging current flows
through the parasitic diode in the charging control FET. At this moment the VM pin potential becomes V
f
, the
voltage for the parasitic diode, higher than V
SS
level. When the battery voltage goes under the overcharge
detection voltage (V
CU
) and provided that the VM pin voltage is higher than the overcurrent 1 detection voltage, the
S-8261 Series releases the overcharge condition.
Caution 1. If the battery is charged to a voltage higher than the overcharge detection voltage (V
CU
) and the
battery voltage does not fall below the overcharge detection voltage (V
CU
) even when a heavy load
is connected, the detection of overcurrent 1, overcurrent 2 and load short-circuiting do not
function until the battery voltage falls below overcharge detection voltage (V
CU
). Since an actual
battery has an internal impedance of several dozens of mΩ, the battery voltage drops immediately
after a heavy load that causes overcurrent is connected, and the detection of overcurrent 1,
overcurrent 2 and load short-circuiting function.
2. When a charger is connected after the overcharge detection, the overcharge condition is not
released even if the battery voltage is below the overcharge release voltage (V
CL
). The overcharge
condition is released when the VM pin voltage goes over the charger detection voltage (V
CHA
) by
removing the charger.