fs356a Fortune Semiconductor Corporation, fs356a Datasheet - Page 9

• Manufacturer Part Number: fs356a
• Description: One Cell Lithium-ion/polymer Battery Protection Ic
• Manufacturer: Fortune Semiconductor Corporation

Rev. 1.2
11. Description of Operation
Normal Condition
The FS356 monitors the voltage of the battery connected between VDD and VSS pin and the voltage difference
between CSI and VSS pin to control charging and discharging. When Vdet2<VDD<Vdet1 and
Vdet4<VCSI<Vdet3, the IC turns the charging (M2) and discharging (M1) control FETs on. The charging and
discharging processes can be operated normally. This condition is called the normal condition.
Note: When a battery is connected to the IC for the first time, the IC may not enter the normal condition (not
Overcharge Condition
When the battery voltage becomes higher than the overcharge detection voltage (Vdet1) during charging under
the normal condition and the detection continues for the overcharge detection delay time (tVdet1) or longer, the
FS356 turns M2 off to stop charging. This condition is called the overcharge condition.
Release of Overcharge Condition
There are two ways to return to normal condition from overcharge condition.
When the battery is self discharging, if VDD<Vdet1 and Vdet3>VCSI>Vdet4 occurs, M2 is to be turned on and
back to normal condition.
Remove the charger and connected to a load, so that the discharging current flows through the parasitic diode
in M2. At this moment VCSI increases momentarily Vf voltage of the parasitic diode from the VSS level. If
VCSI>Vdet3 and VDD<Vdet1 occurs, M2 is to be turned on and back to normal condition.
Note 1: After entering the overcharge condition, if the charger is not removed and Vdet3>VCSI>Vdet4, then M2
Note 2: After entering the overcharge condition, if the charger is not removed and VCSI<Vdet4, then M2 will be
Overdischarge Condition
When the battery voltage falls below the overdischarge detection voltage (Vdet2) during discharging under the
normal condition and the detection continues for the overdischarge detection delay time (tVdet2) or longer, the
FS356 turns M1 off to stop discharging. This condition is called the overdischarge condition. In the meanwhile,
CSI is pulled to VDD by way of internal resistance, RCSID. If VCSI>Vshort, the protection IC enters into
Power-down mode. (Its current consumption is lower than 0.1uA).
Release of Power-down mode
After entering Power-down mode, if the system is connected to a charger, and the charging current flows
through the parasitic diode in M1. If VCSI<Vshort occurs, then it will release Power-down mode. If keeping
charging, there are two ways to enter the normal condition.
Charger Detection
In Power-down mode, when connecting to a charger, if VCSI<Vdet4, then M1 will be turned on when
VDD>Vdet2, and the system will enter the normal condition as described in 1) of previous section, because the
charger detection function is enabled. This action is called charger detection.
dischargeable condition). If this occurs, set the CSI pin voltage equal to the VSS voltage (short the CSI
and VSS pins or connect a charger) to enter the normal condition.
will be turned on when the voltage of the battery is lower than Vdet1 (because the self-discharge of the
battery). The system can enter the charge status again as 1).
kept off even though the voltage of the battery is lower than Vdet1 (because the self-discharge of the
battery), and the system will not enter the charge status.
1)
2)
If VCSI<Vdet4 (Charger detection), then when VDD>Vdet2, M1 will be turned on, and the
system enters the normal condition.
If Vdet4<VCSI<Vshort, then it must be VDD>Vdet2 for M1 to be turned on, and make the
system enter the normal condition.
FS356
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