BATTERY PROTECTION IC FOR 2-SERIAL-CELL PACK
S8232 Series Rev.6.1_00
Seiko Instruments Inc.
14
Operation
Remark Refer to “ Battery Protection IC Conne ction Example”.
Normal Status *1, *2
This IC monitors the voltages of the two serially connected batteries and the discharge current to control charging and
discharging. When the voltages of two batteries are more than the overdischarge detecti on voltage (V
DD1, 2
), le ss than
the overcharge detection voltage (V
CU1, 2
), and the current flowing through the batteries b ecomes equal or lower than a
specified value (the VM pin voltage is equal or lower than overcurrent detection voltage 1), the charging and
discharging FETs are turned on. In this status, charging and discharging can be carried out freely. This is normal
status. In this status, the VM and VSS pins are shorted by the RVSM resistor.
Overcurrent Status
When the discharging current becomes equal to or higher than a specified value (the VM pin voltage is equal to or
higher than the overcurrent detection voltage1) during discharging under the normal status and it continues for the
overcurrent detection delay time (t
IOV1
) or longer, the discharging FET is turned off to stop discharging. This is
overcurrent status. The VM and VSS pins are shorted by the RVSM resistor in this status. The charging FET is also
turned off. While the discharging FET is off and a load is connected, the VM pin voltage is equal to the V
CC
potential.
The overcurrent status returns to the normal status when impedance between the EB
−
and EB
+
pins (refer to
Figure
8
) is 200 M
Ω
or higher, by action such as releasing the load. When the load is released, the VM pin, which is shorted
to the VSS pin by the RVSM resistor, goes back to the V
SS
potential. The IC detects that the VM pin potential returns
to overcurrent detection voltage 1 (V
IOV1
) or lower and returns to the normal status.
Overcharge Status
Following two cases are detected as overch arge status :
(1) If any of the battery voltages becomes higher than the overcharge detection voltage (V
CU1, 2
) during charging
under the normal status and it continu es for the overcharge detection delay time (t
CU1, 2
) or longer, the charging
FET turns off to stop charging. This is overcharge status. In this status, the VM and VSS pins are shorted by
the RVSM resistor.
(2) Although the status is shorter than the overcharge detection delay time (t
CU1, 2
), if any of the battery voltages
becomes higher than the auxiliary overcharge detection voltage (V
CUaux1, 2
), the charging FET turns off to stop
charging. This is also overcharge status. In this status, the VM and VSS pins are shorted by the RVSM
resistor.
The auxiliary overcharge detection voltages ( V
CUaux1, 2
) are correlated with the overchar ge detection voltages (V
CU1, 2
)
and are defined by following equati ons :
V
CUaux1, 2
[V]
=
1.25
×
V
CU1, 2
[V]
or V
CUaux1, 2
[V]
=
1.11
×
V
CU1, 2
[V]
The overcharge status is released in two cases :
(1) The battery voltage which exceeded the overcharge detection voltage (V
CU1, 2
) falls below the overcharge
release voltage (V
CD1, 2
), the charging FET turns on and the IC returns to the normal status.
(2) If the battery voltage which exceeded the overcharge detection voltage (V
CU1, 2
) is equal or higher than the
overcharge release voltage (V
CD1, 2
), however, discharging starts with removing the char ger and connecting the
load, the charging FET turns on and the IC returns to the normal status.
The mechanism to release is as follows: the discharge current flows via an internal parasitic diode of the charging
FET, immediately after connecting the load and discharging starts. Therefore the VM pin’s voltage momentarily
increases about 0.6 V (voltage as much as V
F
voltage of the diode has) plus the VSS pin’s voltage. The IC detects this
voltage by using overcurrent detection voltage 1 (V
IOV1
) so that the IC releases the overcharge status and returns to
the normal status.
Overdischarge Status
If any of the battery voltages falls below the overdischarge detection voltage (V
DD1, 2
) during discharging under the
normal status and it continues for the overdischarge detection delay time (t
DD1, 2
) or longer, the discharging FET turns
off and discharging stops. This is overdischarge status. When the discharging FET turns off, the VM pin voltage
becomes equal to the V
CC
voltage and the IC’s current consumption falls below the power-down current consumptio n
(I
PDN
). This is power-down status. The VM and VCC pins are shorted by the RVCM resistor in the overdischarg e and
power-down statuses.
The power-down status is released when the charger is connected and the voltage between VM and VCC is
overcurrent detection voltage 2 or higher. In this status, When all the battery voltages becomes equal to or higher
than the overdischarge release voltage (V
DU1, 2
) in this status, The IC returns to the normal status from the
overdischarge status.