BATTERY PROTECTION IC FOR 1-CELL PACK
Rev.7.5_00 S-8211C Series
Seiko Instruments Inc. 19
Operation
Remark Refer to " Battery Protection IC Connection Example".
1. Normal status
The S-8211C Series monitors the voltage of the battery connected between the VDD pin and VSS pin and the
voltage difference between the VM pi n and VSS pin to control chargi ng and discharging. When the b attery voltage is
in the range from overdischarge detection voltage (VDL) to overcharge detection voltage (VCU), and the VM pin
voltage is in the range from the charge overcurrent detection voltage (VCIOV) to discharge overcurrent detection
voltage (VDIOV), the S-8211C Series turns both the charging and discharging contro l FETs on. This condition is called
the normal status, and in this condition charg ing and discharging can be carried out freely.
The resistance (RVMD) between the VM pin a nd VDD pin, and the res istance (RVMS) bet ween the VM pin and VSS pin
are not connected in the normal status.
Caution When the battery is conn ected fo r the first time, d ischar ging may not be enabled . In this cas e, short
the VM pin and VSS pin, or set the VM pin’s voltage at the level of the charge overcurrent detection
voltage (VCIOV) or more and the discharge overcurrent detection voltage (VDIOV) or less by
connecting the charg er. T h e S-8211C Series then returns to the normal status.
2. Overcharge status
When the battery voltage becomes higher than overcharge detection voltage (VCU) during charging in the normal
status and detection continues for the overcharge detection delay time (tCU) or longer, the S-8211C Series turns the
charging control FET off to stop charging. This condition is called the overcharge status.
The resistance (RVMD) between the VM pin a nd VDD pin, and the resistan ce (RVMS) bet ween the VM pin and VSS pin
are not connected in the overcharge status.
The overcharge status is released in the following two cases ( (1) and (2) ).
(1) In the case that the VM pin voltage is higher than or equal to the charge overcurrent detection voltage (VCIOV),
and is lower than the discharge overcurrent detection voltage (VDIOV), the S-8211C Series releases the
overcharge status when the battery voltage f alls b elow the overcharge release voltage (VCL).
(2) In the case that the VM pin voltage is higher than or equa l to the dischar ge overcurr ent det ection voltag e (V DIOV),
the S-8211C Series releases the overcharge status when the battery voltage falls below the overcharge
detection voltage (VCU).
The discharge is started by connectin g a load after the overcharge detection, the VM pin voltage rises more than
the VSS pin voltage due to the Vf voltage of the parasitic diode, because the discharge current flows through the
parasitic diode in the charging control FET. If this VM pin voltage is higher than or equal to the discharge
overcurrent detection voltag e (VDIOV), the S-8211 C Series re leas es the ov ercharg e status when the batter y voltage
is lower than or equal to the overchar ge detection voltage (VCU).
For the actual application boards, changing the batter y voltage and the charger voltage simultaneousl y enables to
measure the overcharge release voltage (VCL). In this case, the charger is always necessary to have the
equivalent voltage level to the battery voltage. The charger keeps VM pin voltage higher than or equal to the
charge overcurrent detection voltage (VCIOV) and lower than or equal to the discharge overcurrent detection
voltage (VDIOV). The S-8211C Series releases the overcharge status when the battery voltage falls below the
overcharge release voltage (V CL).
Caution 1. If the battery is charged to a voltage higher than overcharge detection voltage (VCU) and the
battery voltage does not fall below o vercharge detection voltage (VCU) even when a h eavy load is
connected, discharge overcurrent detection and load short-circuiting detection do not function
until the battery voltage falls below overcharge detection voltage (VCU). Since an actual battery
has an internal impedance of tens of mΩ, the battery voltage drops immediately after a heavy
load that causes o vercurren t is connected, and discharge overcurren t detection and load short-
circuiting detection functio n.
2. When a charger is connected after overcharge detection, the overcharge status is not released
even if the battery voltage is below overcharge release voltage (VCL). The overcharge status is
released when the VM pin voltage goes o ver the charge o vercurrent detection voltage (VCIOV) by
removing the charger.