S8209A Datasheet, PDF (7/22 Pages) Seiko Instruments Inc – A protection circuit with series multi-cell 2 cells or more

CMOS IC Application Note
Rev.1.5_00
S-8209A Series Usage Guidelines
1. 2. 4 Charge cell-balance function
In Figure 1, The S-8209A (3) sets the CB3 pin at the level of VDD3 pin when BAT3 gets the cell-balance
detection voltage (V_BU) or more by charging. By this operation, the cell-balance control FET (CBFET3) is turned
on so that the cell-balance control FET bypasses the charge current which flows into BAT3.
At this point, if BAT1, BAT2 are less than V_BU, the speed to charge BAT3 gets slower than to charge BAT1,
BAT2. This is the charge cell-balance function. Even if any of battery voltages reaches V_BU, the cell-balance
control FET which corresponds to each battery turns on and the cell-balance is adjusted.
The S-8209A Series turns off the cell-balance control FET when the battery voltage decreases to the
cell-balance release voltage (V_BL) or less by discharging again.
Caution If a battery having the voltage V_BL or more is included among batteries when composing a
protection circuit shown in Figure 1, the cell-balance control FET may turn on immediately after
connecting the batteries.
1. 2. 5 Delay circuit
Connecting a delay capacitor only to the CDT1 pin of the S-8209A (1), as seen in Figure 1, allows to gain the
detection delay time (t_DET) and the release delay time (t_REL). In detecting by any of batteries, each delay time is
the same length.
(1) Detection delay time (t_DET)
BAT3 gets V_CU or more by charging, the CTLC2 pin gets the level of VDD2 pin because a capacitor is not
connected to the CDT3 pin so that the CO3 pin is set in high impedance after delay of several hundred μs.
After that in the S-8209A (2), the level of CTLC2 pin gets V_CTLCH or more, after delay of several hundred μs
the CO2 pin is set in high impedance.
In the S-8209A (1), after delay of 10.0 [MΩ] (Typ.) × 0.01 [μF] = 0.1 [s] (Typ.), the CO1 pin is set in high
impedance because connected C_CDT to the CDT1 pin.
Even if any of batteries detects, by this operation, users are able to gain the detection delay time almost the
same to delay time of the S-8209A (1), because it defines the whole delay time in the S-8209A Series.
(2) Release delay time (t_REL)
The S-8209A Series also has the release delay time (t_REL), and this delay time is set its length as approx. 1/10
of the detection delay time. Connecting a delay capacitor only to the CDT1 pin of the S-8209A (1) allows
having the same release delay time, as well as in the detection delay time.
Seiko Instruments Inc.
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