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參數資料
| 型號： | 935270462518 |
| 廠商： | NXP SEMICONDUCTORS |
| 元件分類： | 電源管理 |
| 英文描述： | 2-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO8 |
| 封裝： | 4.40 MM, PLASTIC, SOT-530-1, VSOP-8 |
| 文件頁數： | 6/10頁 |
| 文件大小： | 131K |
| 代理商： | 935270462518 |
Philips Semiconductors
Product data
NE57607
Two-cell Lithium-ion battery protection with
overcurrent, over- and under-voltage protection
2001 Oct 03
5
TECHNICAL DISCUSSION
Lithium cell safety
Lithium-ion and lithium-polymer cells have a higher energy density
than that of nickel-cadmium or nickel metal hydride cells and have a
much lighter weight. This makes the lithium cells attractive for use in
portable products. However, lithium cells require a protection circuit
within the battery pack because certain operating conditions can be
hazardous to the battery or the operator, if allowed to continue.
Lithium cells have a porous carbon or graphite anode where lithium
ions can lodge themselves in the pores. The lithium ions are
separated, which avoids the hazards of metallic lithium.
If the lithium cell is allowed to become overcharged, metallic lithium
plates out onto the surface of the anode and volatile gas is
generated within the cell. This creates a rapid-disassembly hazard
(the battery ruptures). If the cell is allowed to over-discharge (Vcell
less than approximately 2.3 V), then the copper metal from the
cathode goes into the electrolyte solution. This shortens the cycle
life of the cell, but presents no safety hazard. If the cell experiences
excessive charge or discharge currents, as happens if the wrong
charger is used, or if the terminals short circuit, the internal series
resistance of the cell creates heating and generates the volatile gas
which could rupture the battery.
The protection circuit continuously monitors the cell voltage for an
overcharged condition or an overdischarged condition. It also
continuously monitors the output for an overcurrent condition. If
any of these conditions are encountered, the protection circuit opens
a series MOSFET switch to terminate the abnormal condition. The
lithium cell protection circuit is placed within the battery pack very
close to the cell.
Charging control versus battery protection
The battery pack industry does not recommend using the pack’s
internal protection circuit to end the charging process. The external
battery charger should have a charge termination circuit in it, such
as that provided by the SA57611. This provides two levels of
overcharge protection, with the primary protection of the external
charge control circuit and the backup protection from the battery
pack’s protection circuit. The charge termination circuit will be set to
stop charging at a level around 50 mV less than the overvoltage
threshold voltage of the battery pack’s own protection circuit.
Lithium cell operating characteristics
The internal resistance of lithium cells is in the 100 m
range,
compared to the 5–20 m
of the nickel-based batteries. This makes
the Lithium-ion and polymer cells better for lower battery current
applications (less than 1 ampere) as found in cellular and wireless
telephones, palmtop and laptop computers, etc.
The average operating voltage of a lithium-ion or polymer cell is
3.6 V as compared to the 1.2 V of NiCd and NiMH cells. The typical
discharge curve for Lithium cell is shown in Figure 3.
SL01553
100
50
2.0
OPEN-CIRCUIT
CELL
VOL
T
AGE
(V)
3.0
4.0
NORMALIZED CELL CAPACITY (%)
VUV
VOV
Figure 3. Lithium discharge curve.
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