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参数资料
| 型号： | LT3505EMS8E#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 19/24页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 1.2A 8MSOP |
| 标准包装： | 50 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 0.78 V ~ 33.8 V |
| 输入电压： | 3.6 V ~ 36 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 200kHz ~ 3.01MHz |
| 电流 - 输出： | 1.2A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-TSSOP，8-MSOP（0.118"，3.00mm 宽）裸露焊盘 |
| 包装： | 管件 |
| 供应商设备封装： | 8-MSOP-EP |
| 产品目录页面： | 1331 (CN2011-ZH PDF) |
LT3505
APPLICATIONS INFORMATION
g m =
200 μ A/V
+
C1
capacitor(C C )andaresistor(R C )inseriestogroundare
used. In addition, a lower value ?lter capacitor (C F ) may be
added in parallel. The ?lter capacitor is not a part of the loop
compensation but is used to ?lter noise at the switching
frequency, and is required only if a phase-lead capacitor
is used or if the output capacitor has high ESR.
Loop compensation determines the stability and transient
performance. Designing the compensation network is a bit
complicated and the best values depend on the application
and in particular the type of output capacitor. A practical
approach is to start with one of the circuits in this data
sheet that is similar to your application and tune the com-
pensation network to optimize the performance. Stability
should then be checked across all operating conditions,
including load current, input voltage and temperature. The
LT1375 data sheet contains a more thorough discussion of
loop compensation and describes how to test the stability
using a transient load.
LT3505
0.8V
V C
R C
C F C C
PCB Layout
CURRENT MODE
POWER STAGE
SW
1.1A/V
R1 C PL
FB
g m =
ESR
780mV
ERROR
AMPLIFIER
2M
R2
Figure 11. Model for Loop Response
OUT
C1
3505 F11
8 V C
FB
4
5
Figure11showsanequivalentcircuitfortheLT3505control
loop. The error amp is a transconductance ampli?er with
?nite output impedance. The power section, consisting of
the modulator, power switch and inductor, is modeled as
a transconductance ampli?er generating an output cur-
rent proportional to the voltage at the V C node. Note that
the output capacitor integrates this current and that the
capacitor on the V C node (C C ) integrates the error ampli-
?er output current, resulting in two poles in the loop. R C
provides a zero. With the recommended output capacitor,
the loop crossover occurs above the R C C C zero. This simple
model works well as long as the value of the inductor is
not too high and the loop crossover frequency is much
lower than the switching frequency. With a larger ceramic
capacitor (very low ESR), crossover may be lower and a
phase lead capacitor (C PL ) across the feedback divider may
improve the phase margin and transient response. Large
electrolytic capacitors may have an ESR large enough to
create an additional zero and the phase lead may not be
necessary.
If the output capacitor is different than the recommended
capacitor, stability should be checked across all operat-
ing conditions, including load current, input voltage and
temperature.
For proper operation and minimum EMI, care must be taken
during printed circuit board layout. Figure 12 shows the
recommended component placement with trace, ground
plane and via locations. Note that large, switched currents
?ow in the LT3505’s V IN and SW pins, the catch diode (D1)
and the input capacitor (C2). The loop formed by these
components should be as small as possible and tied to
SYSTEM
GROUND V OUT
: VIAS TO LOCAL GROUND PLANE
: OUTLINE OF LOCAL GROUND PLANE
C1
V OUT
BOOST
SW
1
2 7
3 6 R T
D1
C2
POWER SIGNAL
GROUND GROUND
3505 F12
V IN SHUTDOWN
Figure 12. A Good PCB Layout Ensures Proper, Low EMI Operation
3505fc
19
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| LT3505IDD#PBF | 功能描述:IC REG BUCK ADJ 1.2A 8DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:250 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V 输入电压:2.05 V ~ 6 V PWM 型:电压模式 频率 - 开关:2MHz 电流 - 输出:500mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:6-UFDFN 包装:带卷 (TR) 供应商设备封装:6-SON（1.45x1） 产品目录页面:1032 (CN2011-ZH PDF) 其它名称:296-25628-2 |
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