参数资料
型号: LTC1550CS8-4.1
厂商: Linear Technology
文件页数: 8/12页
文件大小: 0K
描述: IC REG SWITCHED CAP INV 8SOIC
标准包装: 100
类型: 切换式电容器(充电泵),反相
输出类型: 固定
输出数: 1
输出电压: -4.1V
输入电压: 4.5 V ~ 6.5 V
频率 - 开关: 900kHz
电流 - 输出: 20mA
同步整流器:
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
LTC1550/LTC1551
APPLICATIO N S I N FOR M ATIO N
output capacitors provide lower output ripple. To keep
ripple below 1mV P-P , 10 μ F or greater, with a 0.1 μ F ceramic
capacitor in parallel, is required. At least 4.7 μ F is required
at the output under all conditions to guarantee loop
stability.
Figure 3 shows a marked decrease in peak-to-peak output
ripple when a 0.1 μ F ceramic capacitor added in parallel
with the tantalum output capacitor. The additional ripple
with the tantalum output capacitor alone is mostly very
high order harmonics of the 900kHz clock, which appear
as sharp "spikes" at the output. The energy in these spikes
is very small and they do not contribute to the RMS output
voltage, but their peak-to-peak amplitude can be several
millivolts under some conditions. A garden variety 0.1 μ F
ceramic capacitor has significantly lower impedance at the
spike frequency than even a large tantalum capacitor, and
helps eliminate most of these left-over switching spikes
that the tantalum capacitor leaves behind. Figure 4 and 5
show scope photos of the output of Figure 3 with and
without the additional ceramic capacitor at the output.
A series RC or LC filter can reduce high frequency output
noise even further. Due to the high 900kHz switching
frequency, not much R or L is required; a ferrite bead or a
relatively long PC board trace in series with 0.1 μ F ceramic
capacitor will usually keep the output ripple well below
1mV P-P . The cover page shows an example of an ultralow
8
7
6
WITHOUT 0.1 μ F
V CC = 6V
T A = 25 ° C
C IN = 4.7 μ F
V CC
1
SHDN
SENSE
8
5
+
C IN
4.7 μ F
2
3
4
V CC CP OUT
C1 + GND
LTC1551
V OUT C1 –
7
6
5
C CP
0.1 μ F
4
3
2
1
WITH 0.1 μ F
*C L IS OPTIONAL
C1
0.1 μ F
C OUT
10 μ F
C L
0.1 μ F*
V OUT
– 4.1V
1550/51 F03
0
1
10 100
OUTPUT CAPACITANCE ( μ F)
LTC1550/51 ? F04
V OUT
AC COUPLE
5mV/DIV
Figure 2. Output Ripple Test Circuit
Figure 3. Output Ripple vs Output Capacitance
V OUT
AC COUPLE
2mV/DIV
5 μ s/DIV
LTC1550/51 ? F03
10 μ s/DIV
LTC1550/51 ? F04
8
Figure 4. Output Ripple with 10 μ F Tantalum Capacitor
Figure 5. Output Ripple with 10 μ F Tantalum
Capacitor Paralleled with 0.1 μ F Ceramic Capacitor
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