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参数资料
| 型号： | LT1110CS8#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 9/16页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK BOOST ADJ 0.4A 8SOIC |
| 标准包装： | 100 |
| 类型： | 降压（降压），升压（升压） |
| 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： | 70kHz |
| 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： | 管件 |
| 供应商设备封装： | 8-SOIC |
LT1110
A PPLICATI
S I FOR ATIO
switch closes, current in the inductor builds according to
capacitors provide still better performance at more ex-
()
? – R ' t ?
I L + =
1 – e L ?
?
? ?
V L
R '
where R' = 0.65 ? + DCR L
( 15 )
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,
Figures 1, 2 and 3 show the output voltage of an LT1110
based converter with three 100 μ F capacitors. The peak
P L = ( | ? 5 V | + 0 . 5 V )( 75 mA ) = 413 mW .
= = 5 . 9 μ J .
V L = V IN – 0.75V
As an example, suppose –5V at 75mA is to be generated
from a 4.5V to 5.5V input. Recalling Equation (14),
( 16 )
Energy required from the inductor is
P L 413mW
( 17 )
f OSC 70 kHz
Picking an inductor value of 56 μ H with 0.2 ? DCR results
in a peak switch current of
switch current is 500mA in all cases. Figure 1 shows a
Sprague 501D, 25V aluminum capacitor. V OUT jumps by
over 120mV 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 240m ? . Figure 2 shows the
same circuit, but with a Sprague 150D, 20V tantalum
capacitor replacing the aluminum unit. Output jump is
now about 35mV, corresponding to an ESR of 70m ? .
Figure 3 shows the circuit with a 16V OS-CON unit. ESR is
now only 20m ? .
( ) V ? 1 – e – 0 . 85 ? ? 10 μ s ? = 621 mA .
( 0 . 65 ? + 0 . 2 ? ) ? ?
?
I PEAK =
4 . 5 V – 0 . 75
56 μ H ?
( 18 )
Substituting I PEAK into Equation (04) results in
E L =
1
2
(
56 μ H )( 0 . 621 A ) 2 = 10 . 8 μ J .
( 19 )
5 μ s/DIV
Figure 1. Aluminum
LT1110 ? TA19
Since 10.8 μ J > 5.9 μ J, the 56 μ H inductor will work.
With this relatively small input range, R LIM is not usually
necessary and the I LIM pin can be tied directly to V IN . As in
the step-down case, peak switch current should be limited
to ~800mA.
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
5 μ s/DIV
Figure 2. Tantalum
5 μ s/DIV
LT1110 ? TA20
LT1110 ? TA21
Figure 3. OS-CON
9
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