Electronic Components Datasheet Search |
|
LM3641 Datasheet(PDF) 8 Page - National Semiconductor (TI) |
|
|
LM3641 Datasheet(HTML) 8 Page - National Semiconductor (TI) |
8 / 16 page Product Description (Continued) NORMAL TERMINATION OF CHARGING As you can see in Figure 1, the cell voltage must exceed V MAX for 4 consecutive samples before the MOSFET pair is turned OFF (1). Once V MAX is exceeded, the sampling rate increases to 4 Hz. The sampling rate will return to 1 Hz only after 4 consecutive samples result in V CELL < VMAX. After the MOSFET pair is OFF (2), the voltage across the cell(s) relax and the cell voltage will drop below V MAX. On the next sample, (3), the MOSFET pair will turn ON. As long as the charger is applied and the MOSFET pair turn ON, the cell voltage will exceed V MAX again. The cycle of 4 samples ON a 1 samples OFF will continue until the cell voltage equals V MAX after the MOSFET pair is OFF, (4). This example exag- gerates the rate of these events. The actual operation would result in many ON/OFF cycles at a decreasing duty cycle prior to complete termination of charge. The cell bypass re- sistor will discharge the cell enough to turn on the GATE over a period of minutes. NORMAL TERMINATION OF DISCHARGING The cell voltage must go below V MIN for 4 consecutive samples before the MOSFET pair is turned OFF (1), which is shown in Figure 2. Once the MOSFET pair is OFF and the current is interrupted, the voltage across the cell(s) will in- crease and the cell voltage could exceed V MIN (2). The MOSFET pair remain off until a charger is applied to the pack (3). The presence of a charger turns the MOSFET pair ON. Deeply discharged cells will be charged, although for some narrow bands of V CELL, the GATE may occasionally pulse OFF momentarily. TERMINATION OF ILLEGALLY HIGH CHARGING Should a high charge current be applied to the pack near the end of charge, the cell voltage could exceed V SAFE, which is approximately 100 mV greater than V MAX (1), see Figure 3. On the first detection of a cell voltage in excess of V SAFE- OVERCHARGE , the MOSFET pair will be turned OFF (2). The sample rate increases to 4 Hz after the first detection of V CELL > VMAX. It is desirable under these circumstances for the MOSFET pair to turn ON for only the shortest allowed time period, which is 0.25 seconds. Each sample exceeding V SAFE causes the MOSFET pair to turn OFF (3). Should the cell voltage not drop below V MAX after the MOSFET pair turn OFF, the MOSFET pair remain OFF (4). This example exag- gerates the rate of these events. The actual operation would result in many ON/OFF cycles at a decreasing duty cycle prior to complete termination of charge. LOAD APPLIED IN OVERCHARGED STATE If a load is momentarily applied while the cell is in over- charged state, then the MOSFET pair is momentarily turned ON, see Figure 4. The MOSFET pair will stay ON only as long as the load is applied. The MOSFET pair will stay ON after the load is removed only if the cell voltage remains be- low V MAX for 4 consecutive samples. Possible events are shown as examples of operation: (1) A momentary load is applied to an overcharged cell, the MOSFET pair stay ON only as long as the load is applied. The gate drive is limited so that the MOSFET pair ON volt- age will match a bias voltage generated internal to the IC, V RECOVERY. This bias voltage is the minimum MOSFET ON voltage that allows for the detection of a load. This mode of operation is Active Rectification. Note that the MOSFET pair do not turn ON for the momentary application of a charger. (2) A load is applied for less than 4 samples. The MOSFET pair is ON for the load period, but turn OFF after the load is removed. Only after the 4th sample of V CELL < VMAX will the MOSFET pair turn ON, this time will full drive potential. (3) Assume the application of a charger. Conduction is al- lowed because the FETs are ON, but the MOSFET pair will stay ON only for 4 consecutive overcharge samples. See the diagram for the “Normal Termination of Charging”. (4) The MOSFET pair will turn OFF after the 4 consecutive overcharge samples. (5) A load is applied and after V CELL < VMAX for 4 consecu- tive samples, the MOSFET pair turn ON full. As long as V CELL stays below VMAX, the MOSFET pair will stay ON. Should a load be applied that exceeds the overcurrent- discharge current limit while the IC is in active rectification mode, the MOSFET pair will turn OFF. Recovery requires that either the IC detects a load greater than 3–7 M Ω or that the cell voltage remains under V MAX for 4 samples. If the load that caused overcurrent remains after the cell voltage drops under V MAX for 4 samples, then the MOSFET pair will turn ON once more and normal overcurrent mode is entered. DS012931 12 FIGURE 1. Normal Termination of Charging www.national.com 8 |
Similar Part No. - LM3641 |
|
Similar Description - LM3641 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.NET |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | 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 |