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參數(shù)資料
| 型號： | LM3641M |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 電源管理 |
| 英文描述： | Lithium-Ion Battery Pack Protection Circuit |
| 中文描述： | POWER SUPPLY MANAGEMENT CKT, PDSO8 |
| 封裝： | SOIC-8 |
| 文件頁數(shù)： | 8/17頁 |
| 文件大?。?/td> | 327K |
| 代理商： | LM3641M |
Product Description
(Continued)
NORMAL TERMINATION OF CHARGING
As you can see in Figure 1 the cell voltage must exceed
V
for 4 consecutive samples before the MOSFET pair is
turned OFF (1). Once V
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
<
V
. After
the MOSFET pair is OFF (2), the voltage across the cell(s)
relax and the cell voltage will drop below V
. 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
again. The cycle of 4 samples ON
a 1 samples OFF will continue until the cell voltage equals
V
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
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
(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
, which is
approximately 100 mV greater than V
(1), see Figure 3
On the first detection of a cell voltage in excess of V
OVERCHARGE
, the MOSFET pair will be turned OFF (2). The
sample rate increases to 4 Hz after the first detection of
V
>
V
. 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
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
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
. 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
<
V
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
<
V
for 4 consecu-
tive samples, the MOSFET pair turn ON full. As long as
V
CELL
stays below V
MAX
, 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
or that
the cell voltage remains under V
for 4 samples. If the
load that caused overcurrent remains after the cell voltage
drops under V
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
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