S-8241 Datasheet, PDF (18/38 Pages) Seiko Instruments Inc – BATTERY PROTECTION IC FOR 1-CELL PACK

BATTERY PROTECTION IC FOR 1-CELL PACK
S-8241 Series
Rev.7.6_00
„ Operation
Remark Refer to the “„ Battery Protection IC Connection Example”.
1. Normal Condition
The S-8241 monitors the voltage of the battery connected to VDD and VSS pins and the voltage difference between VM
and VSS pins 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 current flowing through the battery is
equal to or lower than a specified value), the IC turns both the charging and discharging control FETs on. This condition
is called normal condition and in this condition charging and discharging can be carried out freely.
2. Overcurrent Condition
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 voltage) during discharging under normal condition and the state continues for the
overcurrent detection delay time or longer, the S-8241 turns the discharging control FET off to stop discharging. This
condition is called overcurrent condition. (The overcurrent includes overcurrent 1, overcurrent 2, or load
short-circuiting.)
The VM and VSS pins are shorted internally by the R_VMS resistor under the overcurrent condition. When a load is
connected, the VM pin voltage equals the V_DD voltage due to the load.
The overcurrent condition returns to the normal condition when the load is released and the impedance between the
EB+ and EB- pins (see the Figure 12 for a connection example) becomes higher than the automatic recoverable
impedance (see the equation [1] below). When the load is removed, the VM pin goes back to the V_SS potential since the
VM pin is shorted the VSS pin with the R_VMS resistor. Detecting that the VM pin potential is lower than the overcurrent 1
detection voltage (V_IOV1), the IC returns to the normal condition.
Automatic recoverable impedance = {Battery voltage / (Minimum value of overcurrent 1 detection voltage) − 1} x (R_VMS
maximum value) --- [1]
Example: Battery voltage = 3.5 V and overcurrent 1 detection voltage (V_IOV1) = 0.1 V
Automatic recoverable impedance = (3.5 V / 0.07 V −1) x 200 kΩ = 9.8 MΩ
Remark The automatic recoverable impedance varies with the battery voltage and overcurrent 1 detection voltage
settings. Determine the minimum value of the open load using the above equation [1] to have automatic
recovery from the overcurrent condition work after checking the overcurrent 1 detection voltage setting for the
IC.
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Seiko Instruments Inc.