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参数资料
| 型号： | LT1073CS8#TR |
| 厂商： | Linear Technology |
| 文件页数： | 7/16页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK BOOST INV ADJ 8SOIC |
| 标准包装： | 2,500 |
| 类型： | 降压（降压），升压（升压），反相 |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 可调 |
| 输入电压： | 1 V ~ 30 V |
| 频率 - 开关： | 19kHz |
| 电流 - 输出： | 400mA |
| 同步整流器： | 无 |
| 工作温度： | 0°C ~ 70°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 8-SOIC |
LT1073
APPLICATIO S I FOR ATIO
saturation current ratings in the 300mA to 1A range
(depending on application) are adequate. Lastly, the in-
ductor must have sufficiently low DC resistance so that
excessive power is not lost as heat in the windings. An
additional consideration is electro-magnetic interference
(EMI). Toroid and pot core type inductors are recom-
mended in applications where EMI must be kept to a
minimum; for example, where there are sensitive analog
circuitry or transducers nearby. Rod core types are a less
1200
1000
800
600
400
200
expensive choice where EMI is not a problem.
0
0
1
2
3
4
5
= L i PEAK OSC
Specifying a proper inductor for an application requires
first establishing minimum and maximum input voltage,
output voltage and output current. In a step-up converter,
the inductive events add to the input voltage to produce the
output voltage. Power required from the inductor is deter-
mined by:
P L = (V OUT + V D – V IN )(I OUT )
where V D is the diode drop (0.5V for a 1N5818 Schottky).
Maximum power in the inductor is
P L = E L ? f OSC
1 2
? f
2
where
V IN (V)
1073 F02
Figure 2. Maximum Switch Current vs Input Voltage
Capacitor Selection
Selecting the right output capacitor is almost as important
as selecting the right inductor. A poor choice for a filter
capacitor can result in poor efficiency and/or high output
ripple. Ordinary aluminum electrolytics, while inexpensive
and readily available, may have unacceptably poor equiva-
lent series resistance (ESR) and ESL (inductance). There
are low-ESR aluminum capacitors on the market specifi-
cally designed for switch-mode DC/DC converters which
work much better than general purpose units. Tantalum
capacitors provide still better performance at more ex-
pense. We recommend OS-CON capacitors from Sanyo
Corporation (San Diego, CA). These units are physically
quite small and have extremely low ESR. To illustrate,
i PEAK = ? IN ?
?
?
?
? V ?
? R ?
?
?
1– e
– Rt ON ?
L
Figures 3, 4, and 5 show the output voltage of an LT1073
based converter with three 100 μ F capacitors. The peak
switch current is 500mA in all cases. Figure 3 shows a
R = Switch equivalent resistance (1 ? maximum)
added to the DC resistance of the inductor and t ON = ON
time of the switch.
At maximum V IN and ON time, i PEAK should not be allowed
to exceed the maximum switch current shown in Figure 2.
Some input/output voltage combinations will cause con-
tinuous 1 mode operation. In these cases a resistor is
needed between I LIM (Pin 1) and V IN (Pin 2) to keep switch
current under control. See the “Using the I LIM Pin” section
for details.
NOTE 1: i.e., inductor current does not go to zero when the switch is off.
Sprague 501D aluminum capacitor. V OUT jumps by over
150mV when the switch turns off, followed by a drop in
voltage as the inductor dumps into the capacitor. This
works out to be an ESR of over 300m ? . Figure 4 shows the
same circuit, but with a Sprague 150D tantalum capacitor
replacing the aluminum unit. Output jump is now about
30mV, corresponding to an ESR of 60m ? . Figure 5 shows
the circuit with an OS-CON unit. ESR is now only 30m ? .
In very low power applications where every microampere
is important, leakage current of the capacitor must be
considered. The OS-CON units do have leakage current in
the 5 μ A to 10 μ A range. If the load is also in the
7
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