Electronic Components Datasheet Search |
|
SI9730 Datasheet(PDF) 7 Page - Vishay Siliconix |
|
SI9730 Datasheet(HTML) 7 Page - Vishay Siliconix |
7 / 14 page Si9730 Vishay Siliconix Document Number: 70658 S-40135—Rev. F, 16-Feb-04 www.vishay.com 7 DETAILED DESCRIPTION Overview The purpose of the Si9730 is to safely and reliably control the charging and discharging of a two-cell lithium-ion battery (carbon or coke chemistry). It provides protection against all possible fault conditions, including: D external short circuits D reversed charger D overcharged cell or cells D undervoltage D battery open center-tap General Concepts The Si9730 operates by connecting or disconnecting the negative terminal of the battery to the negative side of the load and/or charger (see Figure 8); that is, it does ground side switching. It is important to bear the distinction between these two “grounds” in mind in order to understand the operation of the Si9730. The switching is accomplished by controlling two “back-to-back” MOSFETs: having the two MOSFETs in this arrangement is mandatory to ensure that current cannot flow in either direction when the MOSFETs are off. To turn the switch on, the Si9730 applies a gate-source voltage to both MOSFETs (from the DCO pin) that is high with respect to the sources. The Si9730 DCO signal is referenced to the VM pin while the battery is being charged, and to the Vss pin while the battery is being discharged. The Si9730 causes the DCO to be referenced to the lower of the two voltages. This prevents the switch from turning on or off unintentionally. The Si9730 is designed to operate only with a current-limited lithium-ion battery charger. Specifically, the battery charger must have an open-circuit voltage that does not exceed the absolute maximum IC voltage, and it must have a limited short-circuit current that does not exceed the allowed charging current of the battery. The following descriptions cover all the common operational scenarios; additional information on unusual battery conditions can be found in the state transition table. Normal Charging The cells are in normal charging conditions if a) both cells are above the Over-Discharge Detect Threshold (VODC ~ 2.2 V); b) both cells are under the Over-Charge Detect Threshold (VOC ~ 4.2 V); and c) the center tap is connected to the VC pin. When a charger is present in these conditions, the switch will be on, charging the cells at the current limit of the charger. Normal Discharging The cells are in normal discharging conditions if a, b, and c above are satisfied, and if in addition d) the load current is less than the discharge current limit. With no charger present, the switch will be on, discharging the cells and powering the load. Overcharged Cell(s) Charging The most destructive condition that a LiI+ cell can experience is overcharging. If the cell becomes overcharged beyond its recommended limits, it can become permanently disabled. If one or both cells rise above the over-charge detect threshold (VOC1 and VOC2), and a charger is present, the Si9730 will open the switch (to prevent further charging) and begin bleeding off charge (15-mA typical) from the overcharged cell or cells. The details of this operation depend on the fact that the voltage level of lithium-ion batteries drops for a short time after charging ceases (due to momentary changes in battery chemistry, ESR, etc.). Because of this recovery, the Si9730 allows the battery to continue charging for a short time (the overcharge time, tDL2OC). This additional charge time only occurs if the overcharge condition persists for more than 8 msec (two periods of an internal 4msec oscillator). TDL2OC is determined by the capacitor attached to the CD pin, see Figure 8. Once the overcharge time has ended, the switch is opened, preventing the battery from further overcharging. Now, the Si9730 begins bleeding current off the overcharged cell or cells (IBAL1 and IBAL2), as long as a charger is present. Eventually, the cell(s) will return into their normal range, and charging will begin, starting the whole cycle over again. Overcharged Cell(s) Discharging If one or more cells is overcharged, and a load is connected, the switch is turned on, permitting the battery to power the load. Over-Discharged Cell(s) Discharging Repeated over-discharging of LiI+ cells can cause irreversible reactions in the cells which lead to decreased cycle life. |
Similar Part No. - SI9730 |
|
Similar Description - SI9730 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.COM |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |