参数资料
型号: LTC4008EGN
厂商: Linear Technology
文件页数: 14/24页
文件大小: 0K
描述: IC BATT CHARGER CTRLR 4A 20SSOP
标准包装: 55
功能: 充电管理
电池化学: 多化学
电源电压: 6 V ~ 28 V
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 20-SSOP(0.154",3.90mm 宽)
供应商设备封装: 20-SSOP
包装: 管件
LTC4008
APPLICATIONS INFORMATION
Battery Conditioning
Table 3
Some batteries require a small charging current to condi-
tion them when they are severely depleted. The charging
current is switched to a high rate after the battery voltage
has reached a “safe” voltage to do so. Figure 6 illustrates
how to do this 2-level charging. When Q1 is on, the charger
current is set to maximum. When Q1 is off, the charging
current is set to 10% of the maximum.
FLOAT VOLTAGE (V)
8.2
8.4
12.3
12.6
16.4
16.8
R9 (kΩ) 0.25%
24.9
26.1
15
16.9
11.5
13.3
R8 (kΩ) 0.25%
147
158
140
162
147
174
LTC4008
PROG
10
Soft-Start
The LTC4008 is soft started by the 0.12μF capacitor on
the I TH pin. On start-up, I TH pin voltage will rise quickly to
R1
26.7k
Q1
2N7002
C PROG
0.0047μF
R2
53.6k
4008 F06
0.5V, then ramp up at a rate set by the internal 40μA pull-up
current and the external capacitor. Battery charging current
starts ramping up when I TH voltage reaches 0.8V and full
current is achieved with I TH at 2V. With a 0.12μF capacitor,
time to reach full charge current is about 2ms and it is
assumed that input voltage to the charger will reach full
Figure 6. 2-Level Current Programming
Charger Voltage Programming
A resistor divider, R8 and R9 (see Figure 10), programs
the ?nal ?oat voltage of the charger. The equation for ?oat
voltage is (the input bias current of EA is typically –4nA
and can be ignored):
V FLOAT = V REF (1 + R8/R9)
It is recommended that the sum of R8 and R9 not be less
than 100k. Accuracy of the LTC4008 voltage reference is
±0.8% at 25°C, and ±1% over the full temperature range.
This leads to the possibility that very accurate (0.1%)
resistors might be needed for R8 and R9. Actually, the
temperature of the LTC4008 will rarely exceed 50°C near the
?oat voltage because charging currents have tapered to a low
level, so 0.25% resistors will normally provide the required
level of overall accuracy. Table 3 contains recommended
values for R8 and R9 for popular ?oat voltages.
value in less than 2ms. The capacitor can be increased up
to 1μF if longer input start-up times are needed.
Input and Output Capacitors
The input capacitor (C2) is assumed to absorb all input
switching ripple current in the converter, so it must have
adequate ripple current rating. Worst-case RMS ripple
current will be equal to one-half of output charging current.
Actual capacitance value is not critical. Solid tantalum
low ESR capacitors have high ripple current rating in a
relatively small surface mount package, but caution must
be used when tantalum capacitors are used for input or
output bypass. High input surge currents can be created
when the adapter is hot-plugged to the charger or when
a battery is connected to the charger. Solid tantalum
capacitors have a known failure mechanism when subjected
to very high turn-on surge currents. Kemet T495 series
of “Surge Robust” low ESR tantalums are rated for high
surge conditions such as battery to ground.
4008fb
14
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