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| 型号： | LT3502AEDC#PBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 1.1 A SWITCHING REGULATOR, 2800 kHz SWITCHING FREQ-MAX, PDSO8 |
| 封装： | 2 X 2 MM, LEAD FREE, PLASTIC, DFN-8 |
| 文件页数： | 10/24页 |
| 文件大小： | 386K |
| 代理商： | LT3502AEDC#PBF |
LT3502/LT3502A
18
3502fd
APPLICATIONS INFORMATION
Figure 10. Model for Loop Response
–
+
–
+
800mV
SW
VC
LT3502
GND
3502 F10
R1
OUT
ESR
ERROR
AMPLIFIER
CURRENT MODE
POWER STAGE
FB
R2
1M
RC
150k
CC
70pF
C1
gm =
100μA/V
gm =
1A/V
+
CPL
0.5V
the circuit. In Figure 9b an aluminum electrolytic capacitor
has been added. This capacitor’s high equivalent series
resistance damps the circuit and eliminates the voltage
overshoot. The extra capacitor improves low frequency
ripple ltering and can slightly improve the efciency of the
circuit, though it is likely to be the largest component in the
circuit. An alternative solution is shown in Figure 9c. A 1Ω
resistor is added in series with the input to eliminate the
voltage overshoot (it also reduces the peak input current).
A 0.1μF capacitor improves high frequency ltering. This
solution is smaller and less expensive than the electrolytic
capacitor. For high input voltages its impact on efciency
is minor, reducing efciency less than one half percent for
a 5V output at full load operating from 24V.
Frequency Compensation
The LT3502/LT3502A use current mode control to regulate
the output. This simplies loop compensation. In particular,
the LT3502/LT3502A does not require the ESR of the output
capacitor for stability allowing the use of ceramic capacitors
to achieve low output ripple and small circuit size.
Figure 10 shows an equivalent circuit for the LT3502/
LT3502A control loop. The error amp is a transconductance
amplier with nite output impedance. The power section,
consisting of the modulator, power switch and inductor,
is modeled as a transconductance amplier generating an
output current proportional to the voltage at the VC node.
Note that the output capacitor integrates this current,
Figure 11
BST
DA
GND
D1
FB
VIN
VOUT
L1
C1
C2
C3
R1
R2
= VIA
3502 F11
BD
SHDN
and that the capacitor on the VC node (CC) integrates the
error amplier output current, resulting in two poles in the
loop. RC provides a zero. With the recommended output
capacitor, the loop crossover occurs above the RCCC 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 (CPL) 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. The LT1375 data sheet contains a more
thorough discussion of loop compensation and describes
how to test the stability using a transient load.
PCB Layout
For proper operation and minimum EMI, care must
be taken during printed circuit board layout. Figure 11
shows the recommended component placement with
trace, ground plane and via locations. Note that large,
switched currents ow in the LT3502/LT3502A’s VIN and
SW pins, the catch diode (D1) and the input capacitor (C2).
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相关代理商/技术参数 |
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| LT3502AEDCTRMPBF | 制造商:Linear Technology 功能描述:DC-DC Converter Step-Down 3-40V DFN8EP 制造商:Linear Technology 功能描述:750kHz/2.2MHz 500mA Step-Down Reg LT3502 |
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| LT3502AEMS#PBF | 制造商:Linear Technology 功能描述:DC-DC CONVERTER BUCK 2.2MHZ |
| LT3502AEMS#TRPBF | 功能描述:IC REG BUCK ADJ 0.5A 10MSOP 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:2,500 系列:- 类型:升压（升压） 输出类型:可调式 输出数:1 输出电压:1.24 V ~ 30 V 输入电压:1.5 V ~ 12 V PWM 型:电流模式，混合 频率 - 开关:600kHz 电流 - 输出:500mA 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-SOIC（0.154"，3.90mm 宽） 包装:带卷 (TR) 供应商设备封装:8-SOIC |
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