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| 型号： | LT3508IUF#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 14/26页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 1.4A DL 24QFN |
| 标准包装： | 2,500 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 2 |
| 输出电压： | 0.8 V ~ 35.3 V |
| 输入电压： | 3.7 V ~ 36 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 920kHz ~ 1.06MHz |
| 电流 - 输出： | 1.4A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 24-WFQFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 24-QFN 裸露焊盘（4x4） |
LT3508
APPLICATIONS INFORMATION
The minimum operating voltage of an LT3508 applica-
tion is limited by the undervoltage lockout (≈3.7V) and
by the maximum duty cycle. The boost circuit also limits
the minimum input voltage for proper start-up. If the
input voltage ramps slowly, or the LT3508 turns on when
the output is already in regulation, the boost capacitor
may not be fully charged. Because the boost capacitor
charges with the energy stored in the inductor, the circuit
will rely on some minimum load current to get the boost
circuit running properly. This minimum load will depend
on input and output voltages, and on the arrangement of
the boost circuit. The minimum load current generally
goes to zero once the circuit has started. Figure 5 shows
a plot of minimum load to start and to run as a function
of input voltage. Even without an output load current, in
Minimum Input Voltage, V OUT = 3.3V
many cases the discharged output capacitor will present
a load to the switcher that will allow it to start. The plots
show the worst case, where V IN is ramping very slowly.
Frequency Compensation
The LT3508 uses current mode control to regulate the
output. This simpli?es loop compensation. In particular, the
LT3508 does not require the ESR of the output capacitor
for stability, so you are free to use ceramic capacitors to
achieve low output ripple and small circuit size.
Frequency compensation is provided by the components
tied to the V C pin, as shown in Figure 1. Generally a capaci-
tor (C C ) and a resistor (R C ) in series to ground are used. In
addition, there may be a lower value capacitor in parallel.
This capacitor (C F ) is not part of the loop compensation
but is used to ?lter noise at the switching frequency, and
6.5
6.0
5.5
5.0
4.5
4.0
3.5
T A = 25°C
V OUT = 3.3V
TO RUN
TO START
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
3.0
1
10
100 1000
LOAD CURRENT (mA)
10000
should then be checked across all operating conditions,
including load current, input voltage and temperature. The
3508 F05a
LT1375 data sheet contains a more thorough discussion of
9
8
7
Minimum Input Voltage, V OUT = 5V
T A = 25°C
V OUT = 5V
loop compensation and describes how to test the stability
using a transient load.
Figure 6 shows an equivalent circuit for the LT3508 control
loop. The error ampli?er is a transconductance ampli?er
with ?nite output impedance. The power section, consisting
of the modulator, power switch and inductor, is modeled
6
5
TO RUN
TO START
as a transconductance ampli?er generating an output
current proportional to the voltage at the V C pin. Note that
the output capacitor integrates this current, and that the
capacitor on the V C pin (C C ) integrates the error ampli?er
4
1
10 100 1000
LOAD CURRENT (mA)
10000
3508 G05b
output current, resulting in two poles in the loop. In most
cases a zero is required and comes from either the output
capacitor ESR or from a resistor R C in series with C C .
Figure 5. The Minimum Input Voltage Depends on Output
Voltage, Load Current and Boost Circuit
This simple model works well as long as the value of the
inductor is not too high and the loop crossover frequency
3508fd
14
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相关代理商/技术参数 |
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| LT3509 | 制造商:LINER 制造商全称:Linear Technology 功能描述:36V 500mA Step-Down Regulator and 200mA LDO |
| LT3509EDE#PBF | 功能描述:IC REG BUCK ADJ 0.7A DL 14DFN 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 |
| LT3509EDE#TRPBF | 功能描述:IC REG BUCK ADJ 0.7A DL 14DFN 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:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V，1.5V，1.8V，2.5V 输入电压:2.7 V ~ 20 V PWM 型:- 频率 - 开关:- 电流 - 输出:50mA 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 包装:带卷 (TR) 供应商设备封装:10-MSOP 裸露焊盘 |
| LT3509EDEPBF | 制造商:Linear Technology 功能描述:Sw. Regulator Dual 700mA 3.6-36V DFN14EP |
| LT3509EDE-PBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Dual 36V, 700mA Step-Down Regulator |
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