参数资料
型号: LT1578CS8-2.5#TRPBF
厂商: Linear Technology
文件页数: 22/28页
文件大小: 0K
描述: IC REG BUCK 2.5V 1.5A 8SOIC
标准包装: 2,500
类型: 降压(降压)
输出类型: 固定
输出数: 1
输出电压: 2.5V
输入电压: 4 V ~ 15 V
PWM 型: 电流模式
频率 - 开关: 200kHz
电流 - 输出: 1.5A
同步整流器:
工作温度: 0°C ~ 125°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
LT1578/LT1578-2.5
APPLICATIO N S I N FOR M ATIO N
How Do I Test Loop Stability?
The “standard” compensation for LT1578 is a 100pF
capacitor for C C , with R C = 0. While this compensation will
work for most applications, the “optimum” value for loop
compensation components depends, to various extents,
on parameters which are not well controlled. These in-
clude inductor value ( ± 30% due to production tolerance,
load current and ripple current variations), output capaci-
tance ( ± 20% to ± 50% due to production tolerance,
temperature, aging and changes at the load), output
capacitor ESR ( ± 200% due to production tolerance,
temperature and aging), and finally, DC input voltage and
output load current . This makes it important for the
designer to check out the final design to ensure that it is
One way to check switching regulator loop stability is by
pulse loading the regulator output while observing the
transient response at the output, using the circuit shown
in Figure 13. The regulator loop is “hit” with a small
transient AC load current at a relatively low frequency,
50Hz to 1kHz. This causes the output to jump a few
millivolts, then settle back to the original value, as shown
in Figure 14. A well behaved loop will settle back cleanly,
whereas a loop with poor phase or gain margin will “ring”
as it settles. The number of rings indicates the degree of
stability, and the frequency of the ringing shows the
approximate unity-gain frequency of the loop. Amplitude
of the signal is not particularly important, as long as the
amplitude is not so high that the loop behaves nonlinearly.
“robust” and tolerant of all these variations.
RIPPLE FILTER
SWITCHING
REGULATOR
+
100 μ F TO
1000 μ F
470 ?
3300pF
4.7k
330pF
TO X1
OSCILLOSCOPE
PROBE
ADJUSTABLE
INPUT SUPPLY
ADJUSTABLE
DC LOAD
50 ?
TO
OSCILLOSCOPE
SYNC
100Hz TO 1kHz
100mV TO 1V P-P
1578 F13
Figure 13. Loop Stability Test Circuit
V OUT AT
I OUT = 500mA
BEFORE FILTER
V OUT AT
22
10mV/DIV
5A/DIV
0.2ms/DIV
Figure 14. Loop Stability Check
1578 F14
I OUT = 500mA
AFTER FILTER
V OUT AT
I OUT = 50mA
AFTER FILTER
LOAD PULSE
THROUGH 50 ?
f ≈ 780Hz
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